The Beginning of Variable star astronomy in Hungary

Science.gov (United States)

Zsoldos, Endre

Variable star astronomy began in Hungary as elsewhere: new objects have been recognized in the sky. Comets appeared in 16th - 17th century chronicles. The first mention of the new star of 1572 seems to be the "Prognosticon" of Wilhelm Misocacus, printed in 1578. New stars were discussed in the 17th century by Jesuits as well as Protestants. The work of Jacob Schnitzler is especially interesting from this point. The Cartesians dealt with new stars with less enthusiasm, they hardly mentioned them. The beginning of the 19th century saw the development of science in Hungarian, variable stars, however, were left out. The birth of variable star astronomy might be linked to the Ógyalla Observatory, originally a private observatory of Miklós Konkoly Thege. The 1885 supernova in the Andromeda Nebula were observed there, as well as the spectra of a few interesting variable stars. Theoretical astrophysics also has its beginnings in Ógyalla through the work of Radó Kövesligethy. Professional variable star astronomy started here in the early 20th century through the work of Antal Tass

Photometric search for variable stars in the young open cluster Berkeley 59

Science.gov (United States)

Lata, Sneh; Pandey, A. K.; Maheswar, G.; Mondal, Soumen; Kumar, Brijesh

2011-12-01

We present the time series photometry of stars located in the extremely young open cluster Berkeley 59. Using the 1.04-m telescope at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, we have identified 42 variables in a field of ˜13 × 13 arcmin2 around the cluster. The probable members of the cluster have been identified using a (V, V-I) colour-magnitude diagram and a (J-H, H-K) colour-colour diagram. 31 variables have been found to be pre-main-sequence stars associated with the cluster. 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 masses of these pre-main-sequence variable stars have been found to be in the range of ˜0.3 to ˜3.5 M⊙, and these could be T Tauri stars. The present statistics reveal that about 90 per cent T Tauri stars have period dispersal of the discs of relatively massive stars.

Extreme Variables in Star Forming Regions

Science.gov (United States)

Contreras Peña, Carlos Eduardo

2015-01-01

The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution. The original classification of eruptive variables divides them in two separate subclasses known as FU Orionis stars (FUors) and EX Lupi stars (EXors). 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.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. 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 History of Variable Stars: A Fresh Look

Science.gov (United States)

Hatch, R. A.

2012-06-01

(Abstract only) For historians of astronomy, variable stars are important for a simple reason - stars change. But good evidence suggests this is a very modern idea. Over the millennia, our species has viewed stars as eternal and unchanging, forever fixed in time and space - indeed, the Celestial Dance was a celebration of order, reason, and stability. But everything changed in the period between Copernicus and Newton. According to tradition, two New Stars announced the birth of the New Science. Blazing across the celestial stage, Tycho's Star (1572) and Kepler's Star (1604) appeared dramatically - and just as unexpectedly - disappeared forever. But variable stars were different. Mira Ceti, the oldest, brightest, and most controversial variable star, was important because it appeared and disappeared again and again. Mira was important because it did not go away. The purpose of this essay is to take a fresh look at the history of variable stars. In re-thinking the traditional narrative, I begin with the first sightings of David Fabricius (1596) and his contemporaries - particularly Hevelius (1662) and Boulliau (1667) - to new traditions that unfolded from Newton and Maupertuis to Herschel (1780) and Pigott (1805). The essay concludes with important 19th-century developments, particularly by Argelander (1838), Pickering (1888), and Lockyer (1890). Across three centuries, variable stars prompted astronomers to re-think all the ways that stars were no longer "fixed." New strategies were needed. Astronomers needed to organize, to make continuous observations, to track changing magnitudes, and to explain stellar phases. Importantly - as Mira suggested from the outset - these challenges called for an army of observers with the discipline of Spartans. But recruiting that army required a strategy, a set of theories with shared expectations. Observation and theory worked hand-in-hand. In presenting new historical evidence from neglected printed sources and unpublished

Automated supervised classification of variable stars. I. Methodology

NARCIS (Netherlands)

Debosscher, J.; Sarro, L.M.; Aerts, C.C.; Cuypers, J.; Vandenbussche, B.; Garrido, R.; Solano, E.

2007-01-01

Context: The fast classification of new variable stars is an important step in making them available for further research. Selection of science targets from large databases is much more efficient if they have been classified first. Defining the classes in terms of physical parameters is also

Construction of the Database for Pulsating Variable Stars

Science.gov (United States)

Chen, Bing-Qiu; Yang, Ming; Jiang, Bi-Wei

2012-01-01

A database for pulsating variable stars is constructed to favor the study of variable stars in China. The database includes about 230,000 variable stars in the Galactic bulge, LMC and SMC observed in an about 10 yr period by the MACHO(MAssive Compact Halo Objects) and OGLE(Optical Gravitational Lensing Experiment) projects. The software used for the construction is LAMP, i.e., Linux+Apache+MySQL+PHP. 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.

Construction of Database for Pulsating Variable Stars

Science.gov (United States)

Chen, B. Q.; Yang, M.; Jiang, B. W.

2011-07-01

A database for the pulsating variable stars is constructed for Chinese astronomers to study the variable stars conveniently. The database includes about 230000 variable stars in the Galactic bulge, LMC and SMC observed by the MACHO (MAssive Compact Halo Objects) and OGLE (Optical Gravitational Lensing Experiment) projects at present. The software used for the construction is LAMP, i.e., Linux+Apache+MySQL+PHP. A web page is provided to search the photometric data and the light curve in the database through the right ascension and declination of the object. More data will be incorporated into the database.

The Taiwanese-American occultation survey project stellar variability. III. Detection of 58 new variable stars

Energy Technology Data Exchange (ETDEWEB)

Ishioka, R.; Wang, S.-Y.; Zhang, Z.-W.; Lehner, M. J.; Cook, K. H.; King, S.-K.; Lee, T.; Marshall, S. L.; Schwamb, M. E.; Wang, J.-H.; Wen, C.-Y. [Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Alcock, C.; Protopapas, P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Axelrod, T. [Steward Observatory, 933 North Cherry Avenue, Room N204, Tucson, AZ 85721 (United States); Bianco, F. B. [Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Byun, Y.-I. [Department of Astronomy and University Observatory, Yonsei University, 134 Shinchon, Seoul 120-749 (Korea, Republic of); Chen, W. P.; Ngeow, C.-C. [Institute of Astronomy, National Central University, No. 300, Jhongda Road, Jhongli City, Taoyuan County 320, Taiwan (China); Kim, D.-W. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Rice, J. A., E-mail: ishioka@asiaa.sinica.edu.tw [Department of Statistics, University of California Berkeley, 367 Evans Hall, Berkeley, CA 94720 (United States)

2014-04-01

The Taiwanese-American Occultation Survey project is designed for the detection of stellar occultations by small-size Kuiper Belt Objects, and it has monitored selected fields along the ecliptic plane by using four telescopes with a 3 deg{sup 2} field of view on the sky since 2005. We have analyzed data accumulated during 2005-2012 to detect variable stars. Sixteen fields with observations of more than 100 epochs were examined. We recovered 85 variables among a total of 158 known variable stars in these 16 fields. Most of the unrecovered variables are located in the fields observed less frequently. We also detected 58 variable stars which are not listed in the International Variable Star Index of the American Association of Variable Star Observers. These variable stars are classified as 3 RR Lyrae, 4 Cepheid, 1 δ Scuti, 5 Mira, 15 semi-regular, and 27 eclipsing binaries based on the periodicity and the profile of the light curves.

Variable Star Catalogs: Their Past, Present and Future

Science.gov (United States)

Samus, N. N.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Durlevich, O. V.

2010-02-01

After the second World War, the International Astronomical Union made astronomers of the Soviet Union responsible for variable-star catalogues. This work has been continued ever since the first edition of the General Catalogue of Variable Stars compiled by the team headed by P. P. Parenago and B. V. Kukarkin and published in 1948. Currently, the catalogue work is a joint project of the Institute of Astronomy (Russian Academy of Sciences) and Sternberg Astronomical Institute (Moscow University). This paper is a brief review of recent trends in the field of variable-star catalogues. We discuss problems as well as new prospects related to modern large-scale automatic photometric sky surveys, and outline the state of discussions on the future of the variable-star catalogues in the profile commissions of the IAU.

Variability of X-ray emission from OB stars

International Nuclear Information System (INIS)

Collura, A.; Sciortino, S.; Serio, S.; Vaiana, G. S.; Harnden, F.R. JR.; Osservatorio Astronomico, Palermo, Italy; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA)

1989-01-01

The variability in soft X-ray emission of 12 OB stars is studied. Two different methods of analysis, one more suitable for detecting short-term variations, the other aimed at detecting long time-scale variations, are applied to all stars in the sample. The long-term variability analysis shows that Cyg-OB2 8A Zeta Pup and Delta Ori exhibit significant count rate variations between different data sections. Similar variations are marginally detected in 15 Mon; the count rate variations for the other eight stars are consistent with statistical fluctuations. The light curve of Cyg-OB2 8A suggests the existence of two different emission levels. The short-term variability analysis detects marginal variability in Tau Sco with an effective amplitude of about 30 percent and a time scale of about 50 s. The upper limits to the effective short-term variability amplitude for all other sample stars are in the 10-30 percent range. 30 refs

VARIABLE STARS IN THE GLOBULAR CLUSTER NGC 2808

International Nuclear Information System (INIS)

Kunder, Andrea; Walker, Alistair R.; Stetson, Peter B.; Catelan, Márcio; Amigo, Pía

2013-01-01

The first calibrated broadband BVI time-series photometry is presented for the variable stars in NGC 2808, with observations spanning a range of 28 years. We have also redetermined the variability types and periods for the variable stars identified previously by Corwin et al., revising the number of probable fundamental-mode RR Lyrae variables (RR0) to 11 and the number of first-overtone variables (RR1) to five. Our observations were insufficient to discern the nature of the previously identified RR1 star, V24, and the tentatively identified RR1 star, V13. These two variables are ∼0.8 mag brighter than the RR Lyrae variables, appear to have somewhat erratic period and/or luminosity changes, and lie inside the RR Lyrae instability strip. Curiously, all but one of the RR Lyrae stars studied in this relatively metal-rich cluster exhibit the Blazhko phenomenon, an effect thought to occur with higher frequency in metal-poor environments. The mean periods of the RR0 and RR1 variables are (P) RR0 = 0.56 ± 0.01 d and RR1 = 0.30 ± 0.02 d, respectively, supporting an Oosterhoff I classification of the cluster. On the other hand, the number ratio of RR1-to-RR0-type variables is high, though not unprecedented, for an Oosterhoff I cluster. The RR Lyrae variables have no period shifts at a given amplitude compared to the M3 variables, making it unlikely that these variables are He enhanced. Using the recent recalibration of the RR Lyrae luminosity scale by Catelan and Cortés, a mean distance modulus of (m – M) V = 15.57 ± 0.13 mag for NGC 2808 is obtained, in good agreement with that determined here from its type II Cepheid and SX Phoenicis population. Our data have also allowed the discovery of two new candidate SX Phoenicis stars and an eclipsing binary in the blue straggler region of the NGC 2808 color-magnitude diagram.

Variable stars in the Pegasus dwarf galaxy (DDO 216)

Energy Technology Data Exchange (ETDEWEB)

Hoessel, J.G.; Abbott, M.J.; Saha, A.; Mossman, A.E.; Danielson, G.E. (Washburn Observatory, Madison, WI (USA) Space Telescope Science Institute, Baltimore, MD (USA) Palomar Observatory, Pasadena, CA (USA))

1990-10-01

Observations obtained over a period of five years of the resolved stars in the Pegasus dwarf irregular galaxy (DDO 216) have been searched for variable stars. Thirty-one variables were found, and periods established for 12. Two of these variable stars are clearly eclipsing variables, seven are very likely Cepheid variables, and the remaining three are probable Cepheids. The period-luminosity relation for the Cepheids indicates a distance modulus for Pegasus of m - M = 26.22 + or - 0.20. This places Pegasus very near the zero-velocity surface of the Local Group. 25 refs.

IUE observations of variability in winds from hot stars

Science.gov (United States)

Grady, C. A.; Snow, T. P., Jr.

1981-01-01

Observations of variability in stellar winds or envelopes provide an important probe of their dynamics. For this purpose a number of O, B, Be, and Wolf-Rayet stars were repeatedly observed with the IUE satellite in high resolution mode. In the course of analysis, instrumental and data handling effects were found to introduce spurious variability in many of the spectra. software was developed to partially compensate for these effects, but limitations remain on the type of variability that can be identified from IUE spectra. With these contraints, preliminary results of multiple observations of two OB stars, one Wolf-Rayet star, and a Be star are discussed.

Variable Stars in Large Magellanic Cloud Globular Clusters. III. Reticulum

Science.gov (United States)

Kuehn, Charles A.; Dame, Kyra; Smith, Horace A.; Catelan, Márcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura

2013-06-01

This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. The primary goal of this series is to look at how the characteristics and behavior of RR Lyrae stars in Oosterhoff-intermediate systems compare to those of their counterparts in Oosterhoff-I/II systems. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We found a total of 32 variables stars (22 RRab, 4 RRc, and 6 RRd stars) in our field of view. 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. Based on observations taken with the SMARTS 1.3 m telescope operated by the SMARTS Consortium and observations taken at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

Variable stars in the field of open cluster NGC 2126

International Nuclear Information System (INIS)

Liu Shunfang; Wu Zhenyu; Zhang Xiaobin; Wu Jianghua; Ma Jun; Jiang Zhaoji; Chen Jiansheng; Zhou Xu

2009-01-01

We report the results of a time-series CCD photometric survey of variable stars in the field of open cluster NGC 2126. In about a one square degree field covering the cluster, a total of 21 variable candidates are detected during this survey, of which 16 are newly found. The periods, classifications and spectral types of 14 newly discovered variables are discussed, which consist of six eclipsing binary systems, three pulsating variable stars, three long period variables, one RS CVn star, and one W UMa or δ Scuti star. In addition, there are two variable candidates, the properties of which cannot be determined. By a method based on fitting observed spectral energy distributions of stars with theoretical ones, the membership probabilities and the fundamental parameters of this cluster are determined. As a result, five variables are probably members of NGC 2126. The fundamental parameters of this cluster are determined as: metallicity to be 0.008 Z o-dot , age log(t) = 8.95, distance modulus (m - M) 0 = 10.34 and reddening value E (B - V) = 0.55 mag.

Variable Stars in the Field of V729 Aql

Science.gov (United States)

Cagaš, P.

2017-04-01

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. Also, newly introduced SILICUPS software is intended for post-processing of stored light curves. 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 V729 Aql. and demonstrates the results.

Variable Stars in Large Magellanic Cloud Globular Clusters. II. NGC 1786

Science.gov (United States)

Kuehn, Charles A.; Smith, Horace A.; Catelan, Márcio; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura

2012-12-01

This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series B-V photometric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binaries, 3 Delta Scuti/SX Phoenicis variables, and 2 variables of undetermined type. Photometric parameters for these variables are presented. We present physical properties for some of the RR Lyrae stars, derived from Fourier analysis of their light curves. We discuss several different indicators of Oosterhoff type which indicate that the Oosterhoff classification of NGC 1786 is not as clear cut as what is seen in most globular clusters. Based on observations taken with the SMARTS 1.3 m telescope operated by the SMARTS Consortium and observations taken at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

NEAR-INFRARED VARIABILITY IN YOUNG STARS IN CYGNUS OB7

Energy Technology Data Exchange (ETDEWEB)

Rice, Thomas S. [Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138 (United States); Wolk, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin [Institute for Astronomy, University of Hawaii at Manoa, 640 N Aohoku Pl, Hilo, HI 96720 (United States)

2012-08-10

We present the first results from a 124 night J, H, K near-infrared monitoring campaign of the dark cloud L 1003 in Cygnus OB7, an active star-forming region. Using three seasons of UKIRT observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. On the basis of near-infrared excesses from disks, we identify 30 pre-main-sequence stars, including 24 which are newly discovered. We analyze those stars and find that the NIR excesses are significantly variable. All 9200 stars were monitored for photometric variability; among the field star population, {approx}160 exhibited near-infrared variability (1.7% of the sample). Of the 30 young stellar objects (YSOs), 28 of them (93%) are variable at a significant level. Of the 30 YSOs, twenty-five have near-infrared excess consistent with simple disk-plus-star classical T Tauri models. Nine of these (36%) drift in color space over the course of these observations and/or since Two Micron All Sky Survey observations such that they cross the boundary defining the NIR excess criteria; effectively, they have a transient near-infrared excess. Thus, time-series JHK observations can be used to obtain a more complete sample of disk-bearing stars than single-epoch JHK observations. About half of the YSOs have color-space variations parallel to either the classical T Tauri star locus or a hybrid track which includes the dust reddening trajectory. This indicates that the NIR variability in YSOs that possess accretion disks arises from a combination of variable extinction and changes in the inner accretion disk: either in accretion rate, central hole size, and/or the inclination of the inner disk. While some variability may be due to stellar rotation, the level of variability on the individual stars can exceed a magnitude. This is a strong empirical suggestion that protoplanetary disks are quite dynamic and exhibit more complex activity on short

The Variable Stars of the Draco Dwarf Spheroidal Galaxy: Revisited

Science.gov (United States)

Kinemuchi, K.; Harris, H. C.; Smith, Horace A.; Silbermann, N. A.; Snyder, L. A.; La Cluyzé, A. P.; Clark, C. L.

2008-11-01

We present a CCD survey of variable stars in the Draco dwarf spheroidal galaxy. This survey, which has the largest areal coverage since the original variable star survey by Baade & Swope, includes photometry for 270 RR Lyrae (RRL) stars, 9 anomalous Cepheids (ACs), 2 eclipsing binaries, and 12 slow, irregular red variables, as well as 30 background QSOs. Twenty-six probable double-mode RRL stars were identified. Observed parameters, including mean V and I magnitudes, V amplitudes, and periods, have been derived. Photometric metallicities of the ab-type RRL stars were calculated according to the method of Jurcsik & Kovacs, yielding a mean metallicity of lang[Fe/H]rang = -2.19 ± 0.03. The well-known Oosterhoff intermediate nature of the RRL stars in Draco is reconfirmed, although the double-mode RRL stars, with one exception, have properties similar to those found in Oosterhoff type II globular clusters. The period-luminosity relation of the ACs is rediscussed with the addition of the new Draco ACs.

Combination spectra in long-period variable stars

International Nuclear Information System (INIS)

Bruce, C.E.R.

1975-01-01

The electrical discharge theory of the variation in excitation observed in the atmosphere of the long period variable stars offers an explanation for the combination spectra exhibited by many of these stars, which is shown to be in accord with several of the most outstanding changes in their spectra and magnitude. (author)

Variable stars in metal-rich globular clusters. IV. Long-period variables in NGC 6496

Energy Technology Data Exchange (ETDEWEB)

Abbas, Mohamad A. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Layden, Andrew C.; Guldenschuh, Katherine A. [Physics and Astronomy Department, Bowling Green State University, Bowling Green, OH 43403 (United States); Reichart, D. E.; Ivarsen, K. M.; Haislip, J. B.; Nysewander, M. C.; LaCluyze, A. P. [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599 (United States); Welch, Douglas L., E-mail: mabbas@ari.uni-heidelberg.de, E-mail: laydena@bgsu.edu [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8 S 4M1 (Canada)

2015-02-01

We present VI-band photometry for stars in the metal-rich globular cluster NGC 6496. Our time-series data were cadenced to search for long-period variables (LPVs) over a span of nearly two years, and our variability search yielded the discovery of 13 new variable stars, of which 6 are LPVs, 2 are suspected LPVs, and 5 are short-period eclipsing binaries. An additional star was found in the ASAS database, and we clarify its type and period. We argue that all of the eclipsing binaries are field stars, while five to six of the LPVs are members of NGC 6496. We compare the period–luminosity distribution of these LPVs with those of LPVs in the Large Magellanic Cloud and 47 Tucanae, and with theoretical pulsation models. We also present a VI color–magnitude diagram, display the evolutionary states of the variables, and match isochrones to determine a reddening of E(B−V)= 0.21±0.02 mag and apparent distance modulus of 15.60±0.15 mag.

CHARACTERIZING THE VARIABILITY OF STARS WITH EARLY-RELEASE KEPLER DATA

International Nuclear Information System (INIS)

Ciardi, David R.; Von Braun, Kaspar; Van Eyken, Julian; Kane, Stephen R.; Plavchan, Peter; RamIrez, Solange V.; Bryden, Geoff; Howell, Steve B.; Stauffer, John R.

2011-01-01

We present a variability analysis of the early-release first quarter of data publicly released by the Kepler project. Using the stellar parameters from the Kepler Input Catalog, we have separated the sample into 129,000 dwarfs and 17,000 giants and further sub-divided the luminosity classes into temperature bins corresponding approximately to the spectral classes A, F, G, K, and M. Utilizing the inherent sampling and time baseline of the public data set (30 minute sampling and 33.5 day baseline), we have explored the variability of the stellar sample. The overall variability rate of the dwarfs is 25% for the entire sample, but can reach 100% for the brightest groups of stars in the sample. G dwarfs are found to be the most stable with a dispersion floor of σ ∼ 0.04 mmag. At the precision of Kepler, >95% of the giant stars are variable with a noise floor of ∼0.1 mmag, 0.3 mmag, and 10 mmag for the G giants, K giants, and M giants, respectively. The photometric dispersion of the giants is consistent with acoustic variations of the photosphere; the photometrically derived predicted radial velocity distribution for the K giants is in agreement with the measured radial velocity distribution. We have also briefly explored the variability fraction as a function of data set baseline (1-33 days), at the native 30 minute sampling of the public Kepler data. To within the limitations of the data, we find that the overall variability fractions increase as the data set baseline is increased from 1 day to 33 days, in particular for the most variable stars. The lower mass M dwarf, K dwarf, and G dwarf stars increase their variability more significantly than the higher mass F dwarf and A dwarf stars as the time baseline is increased, indicating that the variability of the lower mass stars is mostly characterized by timescales of weeks while the variability of the higher mass stars is mostly characterized by timescales of days. A study of the distribution of the variability as

Variable K-type stars in the Pleiades

International Nuclear Information System (INIS)

Leeuwen, F. van; Alphenaar, P.

1983-01-01

Photometric observations in the VBLUW system (Lub, 1979) have been performed during 1980 and 1981 of 19 late G and early K-type members of the Pleiades Cluster, in order to study their variability. All stars showed variations with amplitudes of 0.02 to 0.20 magn. in V. For 12 stars light curves were obtained which show periods that range from 0.24 to 1.22 days. The light curves are semi-regular and resemble those of BY Dra stars, although the periods are shorter. (Auth.)

Caroline Furness and the Evolution of Visual Variable Star Observing

Science.gov (United States)

Larsen, Kristine

2017-01-01

An Introduction to the Study of Variable Stars by Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, was published in October 2015. 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. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World’s Fair in Chicago. 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. Furness’s work is therefore a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. Furness’s book and its reception in the scientific community are analyzed, and parallels with (and departures from) the current advice given by the AAVSO to beginning variable star observers today are highlighted.

New Variable Stars in the KP2001 Catalog from the Data Base of the Northern Sky Variability Survey

Science.gov (United States)

Petrosyan, G. V.

2018-03-01

The optical variability of stars in the KP2001 catalog is studied. Monitor data from the automatic Northern Sky Variability Survey (NSVS) are used for this purpose. Of the 257 objects that were studied, 5 are Mira Ceti variables (mirids), 33 are semiregular (SR), and 108 are irregular variables (Ir). The light curves of the other objects show no noticeable signs of variability. For the first time, 11 stars are assigned to the semiregular and 105 stars to the irregular variables. Of the irregular variables, the light curves of two, No. 8 and No. 194, are distinct and are similar to the curves for eclipsing variables. The periods and amplitudes of the mirids and semiregular variables are determined using the "VStar" program package from AAVSO. The absolute stellar magnitudes M K and distances are also estimated, along with the mass loss for the mirids. The behavior of stars from KP2001 in 2MASS and WISE color diagrams is examined.

VizieR Online Data Catalog: AAVSO International Variable Star Index VSX (Watson+, 2006-2014)

Science.gov (United States)

Watson, C.; Henden, A. A.; Price, A.

2018-05-01

This file contains Galactic stars known or suspected to be variable. It lists all stars that have an entry in the AAVSO International Variable Star Index (VSX; http://www.aavso.org/vsx). The database consisted initially of the General Catalogue of Variable Stars (GCVS) and the New Catalogue of Suspected Variables (NSV) and was then supplemented with a large number of variable star catalogues, as well as individual variable star discoveries or variables found in the literature. Effort has also been invested to update the entries with the latest information regarding position, type and period and to remove duplicates. The VSX database is being continually updated and maintained. For historical reasons some objects outside of the Galaxy have been included. (3 data files).

Variable Stars in the M31 Dwarf Spheroidal Companion Cassiopeia

Science.gov (United States)

Pritzl, Barton J.; Armandroff, T. E.; Jacoby, G. H.; Da Costa, G. S.

2007-12-01

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. We will present the results of a variable star search using HST/ACS data, along with a preliminary color-magnitude diagram. 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.This research is supported in part by NASA through grant number GO-11081.11 from the Space Telescope Science Institute.

Revised coordinates of variable stars in Cassiopeia

Science.gov (United States)

Nesci, R.

2018-02-01

The identification of the variable stars published on IBVS 3573 has ben revised on the basis of the original (unpublished) finding charts. Cross check with the 2MASS catalog has been made to get more accurate coordinates and to confirm their nature from their , colors. The Mira stars, given their known periods, could be used with the astrometric parallaxes of the forthcoming Gaia catalog to improve the Period-Luminosity relation.

Search for variable stars in the young open cluster Stock 18

Directory of Open Access Journals (Sweden)

Sinha Tirthendu

2017-01-01

Full Text Available We have carried out multi-epoch deep I band photometry of the open cluster Stock 18 to search for variable stars in star forming regions. In the present study, we report identification of 28 periodic and 165 non-periodic variables stars. The periods of most of the periodic variables are in between 2 to 20 hours and their magnitude varies between 0.05 to 0.6 mag. We have derived spectral energy distributions for 48 probable pre-main sequence variables and the average age and mass is found to be 2.7 ± 0.3 Myrs and 2.7 ± 0.2 M⊙, respectively.

VARIABLE STARS IN LARGE MAGELLANIC CLOUD GLOBULAR CLUSTERS. II. NGC 1786

International Nuclear Information System (INIS)

Kuehn, Charles A.; Smith, Horace A.; De Lee, Nathan; Catelan, Márcio; Pritzl, Barton J.; Borissova, Jura

2012-01-01

This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series B–V photometric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binaries, 3 Delta Scuti/SX Phoenicis variables, and 2 variables of undetermined type. Photometric parameters for these variables are presented. We present physical properties for some of the RR Lyrae stars, derived from Fourier analysis of their light curves. We discuss several different indicators of Oosterhoff type which indicate that the Oosterhoff classification of NGC 1786 is not as clear cut as what is seen in most globular clusters.

VARIABILITY AND STAR FORMATION IN LEO T, THE LOWEST LUMINOSITY STAR-FORMING GALAXY KNOWN TODAY

Energy Technology Data Exchange (ETDEWEB)

Clementini, Gisella; Cignoni, Michele; Ramos, Rodrigo Contreras; Federici, Luciana; Tosi, Monica [INAF, Osservatorio Astronomico di Bologna, I-40127 Bologna (Italy); Ripepi, Vincenzo; Marconi, Marcella; Musella, Ilaria, E-mail: gisella.clementini@oabo.inaf.it, E-mail: rodrigo.contreras@oabo.inaf.it, E-mail: luciana.federici@oabo.inaf.it, E-mail: monica.tosi@oabo.inaf.it, E-mail: michele.cignoni@unibo.it, E-mail: ripepi@na.astro.it, E-mail: marcella@na.astro.it, E-mail: ilaria@na.astro.it [INAF, Osservatorio Astronomico di Capodimonte, I-80131 Napoli (Italy)

2012-09-10

We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way 'ultra-faint' dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 11 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409{sup +29}{sub -27} kpc (distance modulus of 23.06 {+-} 0.15 mag) was derived from the galaxy's RR Lyrae star. Our V, V - I color-magnitude diagram (CMD) of Leo T reaches V {approx} 29 mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the SFH, based on the comparison of the observed V, V - I CMD with the expected distribution of stars for different evolutionary scenarios, confirms that Leo T has a complex SFH dominated by two enhanced periods about 1.5 and 9 Gyr ago, respectively. The distribution of stars and gas shows that the galaxy has a fairly asymmetric structure.

The ASAS-SN Catalog of Variable Stars I: The Serendipitous Survey

Science.gov (United States)

Jayasinghe, T.; Kochanek, C. S.; Stanek, K. Z.; Shappee, B. J.; Holoien, T. W.-S.; Thompson, Todd A.; Prieto, J. L.; Dong, Subo; Pawlak, M.; Shields, J. V.; Pojmanski, G.; Otero, S.; Britt, C. A.; Will, D.

2018-04-01

The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to routinely monitor the whole sky with a cadence of ˜2 - 3 days down to V≲ 17 mag. ASAS-SN has monitored the whole sky since 2014, collecting ˜100 - 500 epochs of observations per field. The V-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. We present a catalog of 66,533 bright, new variable stars discovered during our search for supernovae, including 27,753 periodic variables and 38,780 irregular variables. V-band light curves for the ASAS-SN variables are available through the ASAS-SN variable stars database (https://asas-sn.osu.edu/variables). The database will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey.

Optical photometric variable stars towards the Galactic H II region NGC 2282

Science.gov (United States)

Dutta, Somnath; Mondal, Soumen; Joshi, Santosh; Jose, Jessy; Das, Ramkrishna; Ghosh, Supriyo

2018-05-01

We report here CCD I-band time series photometry of a young (2-5 Myr) cluster NGC 2282, in order to identify and understand the variability of pre-main-sequence (PMS) stars. The I-band photometry, down to ˜20.5 mag, enables us to probe the variability towards the lower mass end (˜0.1 M⊙) of PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H α emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H α emission, near-IR (NIR)/mid-IR (MIR) excess or both and are candidate members of the cluster. Out of 62 variables, 41 are periodic variables, with a rotation rate ranging from 0.2-7 d. The period distribution exhibits a median period at ˜1 d, as in many young clusters (e.g. NGC 2264, ONC, etc.), but it follows a unimodal distribution, unlike others that have bimodality, with slow rotators peaking at ˜6-8 d. To investigate the rotation-disc and variability-disc connection, we derived the NIR excess from Δ(I - K) and the MIR excess from Spitzer [3.6]-[4.5] μm data. No conclusive evidence of slow rotation with the presence of discs around stars and fast rotation for discless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with IR excess is found for all variables.

ROTSE All-Sky Surveys for Variable Stars. I. Test Fields

International Nuclear Information System (INIS)

Akerlof, C.; Amrose, S.; Balsano, R.; Bloch, J.; Casperson, D.; Fletcher, S.; Gisler, G.; Hills, J.; Kehoe, R.; Lee, B.

2000-01-01

The Robotic Optical Transient Search Experiment I (ROTSE-I) experiment has generated CCD photometry for the entire northern sky in two epochs nightly since 1998 March. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering roughly 2000 deg2, we identify 1781 periodic variable stars with mean magnitudes between m v = 10.0 and m v = 15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars. (c) (c) 2000. The American Astronomical Society

The Globular Cluster NGC 6402 (M14). II. Variable Stars

Science.gov (United States)

Contreras Peña, C.; Catelan, M.; Grundahl, F.; Stephens, A. W.; Smith, H. A.

2018-03-01

We present time-series BVI photometry for the Galactic globular cluster NGC 6402 (M14). The data consist of ∼137 images per filter, obtained using the 0.9 and 1.0 m SMARTS telescopes at the Cerro Tololo Inter-American Observatory. The images were obtained during two observing runs in 2006–2007. The image-subtraction package ISIS, along with DAOPHOT II/ALLFRAME, was used to perform crowded-field photometry and search for variable stars. We identified 130 variables, eight of which are new discoveries. The variable star population is comprised of 56 ab-type RR Lyrae stars, 54 c-type RR Lyrae, 6 type II Cepheids, 1 W UMa star, 1 detached eclipsing binary, and 12 long-period variables. 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. By considering all of the RR Lyrae stars as members of the cluster, we derive =0.589 {{d}}{{a}}{{y}}{{s}}. 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 0.9 m and 1 m telescopes at the Cerro Tololo Inter-American Observatory, Chile, operated by the SMARTS consortium.

A PHOTOMETRIC VARIABILITY SURVEY OF FIELD K AND M DWARF STARS WITH HATNet

International Nuclear Information System (INIS)

Hartman, J. D.; Bakos, G. A.; Noyes, R. W.; Sipocz, B.; Pal, A.; Kovacs, G.; Mazeh, T.; Shporer, A.

2011-01-01

Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broadband photometric variability of a sample of 27, 560 field K and M dwarfs selected by color and proper motion (V - K ∼> 3.0, μ > 30 mas yr -1 , plus additional cuts in J - H versus H - K S and on the reduced proper motion). We search the light curves for periodic variations and for large-amplitude, long-duration flare events. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries (EBs), as secure variable star detections that are not obvious blends. We estimate that a further ∼26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including five of the EBs, have previously been identified as variables or are blended with previously identified variables. One of the newly identified EBs is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M 1 = M 2 = 0.258 ± 0.008 M sun and R 1 = R 2 = 0.289 ± 0.007 R sun . The radii of the component stars are larger than theoretical expectations if the system is older than ∼200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs, finding that many of the well-established relations for F, G, and K dwarfs continue into the M dwarf regime. We find that the fraction of stars that is variable with peak-to-peak amplitudes greater than 0.01 mag increases exponentially with the V - K S color such that

Infrared variability and nature of symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Feast, M W; Robertson, B S.C.; Catchpole, R M [Royal Observatory, Cape Town (South Africa)

1977-05-01

Most symbiotic stars may be placed in one of two classes according to their infrared colours. In one group the systems contain an M type giant. In the other there is evidence for a star plus infrared emission from dust. JHKL photometry is given for three members of each class. Photometry of the VV Cephei system FR Sct is also given. No evidence for variability was found for systems without dust. The three systems with dust (RX Pup, RR Tel and PK 280-2/sup 0/.1) each show large variations of the stellar component (..delta..J, 1sup(m).6 to 2sup(m).7). It is concluded that these dusty systems contain Mira variables. For the systems without dust the mass transfer in the system is presumably through the inner Lagrangian point. For systems containing Miras it is possible that the companion accretes matter from a general stellar wind. Symbiotic systems containing Mira variables have more dust than average Mira variables. Either an unusually dense stellar wind is needed to produce a symbiotic system or such a system produces dust, perhaps in a high-density region resulting from the interaction of the stellar wind with the companion.

Investigation of superflares frequency variability of solar-type stars

International Nuclear Information System (INIS)

Akopian, A.A.

2015-01-01

Statistical study of the variability of the superflares frequency of 46 solar-type stars detected by orbital observatory 'Kepler' is presented. Two possible scenarios for changes in frequency are considered. In the first, the temporal sequence of superflares is regarded as a piecewise stationary Poissonian process. Statistically significant change in the frequency of superflares by several times is revealed at five stars. Moments of change of frequency are accompanied by sudden changes in the behavior of the star's brightness. Brightness of a star for a short time becomes irregular, with a significant decrease in the amplitude

Machine learning techniques to select variable stars

Directory of Open Access Journals (Sweden)

García-Varela Alejandro

2017-01-01

Full Text Available In order to perform a supervised classification of variable stars, we propose and evaluate a set of six features extracted from the magnitude density of the light curves. They are used to train automatic classification systems using state-of-the-art classifiers implemented in the R statistical computing environment. We find that random forests is the most successful method to select variables.

Short-term variability and mass loss in Be stars. II. Physical taxonomy of photometric variability observed by the Kepler spacecraft

Science.gov (United States)

Rivinius, Th.; Baade, D.; Carciofi, A. C.

2016-09-01

Context. Classical Be stars have been established as pulsating stars. Space-based photometric monitoring missions contributed significantly to that result. However, whether Be stars are just rapidly rotating SPB or β Cep stars, or whether they have to be understood differently, remains debated in the view of their highly complex power spectra. Aims: Kepler data of three known Be stars are re-visited to establish their pulsational nature and assess the properties of additional, non-pulsational variations. The three program stars turned out to be one inactive Be star, one active, continuously outbursting Be star, and one Be star transiting from a non-outbursting into an outbursting phase, thus forming an excellent sample to distill properties of Be stars in the various phases of their life-cycle. Methods: The Kepler data was first cleaned from any long-term variability with Lomb-Scargle based pre-whitening. Then a Lomb-Scargle analysis of the remaining short-term variations was compared to a wavelet analysis of the cleaned data. This offers a new view on the variability, as it enables us to see the temporal evolution of the variability and phase relations between supposed beating phenomena, which are typically not visualized in a Lomb-Scargle analysis. Results: The short-term photometric variability of Be stars must be disentangled into a stellar and a circumstellar part. The stellar part is on the whole not different from what is seen in non-Be stars. However, some of the observed phenomena might be to be due to resonant mode coupling, a mechanism not typically considered for B-type stars. Short-term circumstellar variability comes in the form of either a group of relatively well-defined, short-lived frequencies during outbursts, which are called Štefl frequencies, and broad bumps in the power spectra, indicating aperiodic variability on a time scale similar to typical low-order g-mode pulsation frequencies, rather than true periodicity. Conclusions: From a

White-dwarf rotational equilibria in magnetic cataclysmic variable stars

Energy Technology Data Exchange (ETDEWEB)

Warner, B. (Cape Town Univ. (South Africa). Dept. of Astronomy Australian National Univ., Canberra (Australia). Dept. of Mathematics); Wickramasinghe, D.T. (Australian National Univ., Canberra (Australia). Dept. of Mathematics)

1991-02-01

The magnetic cataclysmic variable stars (polars, intermediate polars and DQ Her stars) are grouped about three lines in the orbital period-spin period diagram. This segregation is shown to be the consequence of competition between braking and accretion torques when combined with the effects of cyclical variations in rate of mass transfer. (author).

The POINT-AGAPE Survey I: The Variable Stars in M31

CERN Document Server

An Jun Hong; Hewett, P C; Baillon, Paul; Calchi-Novati, S; Carr, B J; Creze, M; Giraud-Héraud, Yannick; Gould, A; Jetzer, P; Kaplan, J; Kerins, E; Paulin-Henriksson, S; Smartt, S J; Stalin, C S; Tsapras, Y; An, Jin H.; Jetzer, Ph.

2004-01-01

The POINT-AGAPE collaboration has been monitoring M31 for three seasons with the Wide Field Camera on the Isaac Newton Telescope. In each season, data are taken for one hour per night for roughly sixty nights during the six months that M31 is visible. The two fields of view straddle the central bulge, northwards and southwards. We have calculated the locations, periods and amplitudes of 35414 variable stars in M31 as a by-product of our microlensing search. The variables are classified according to their period and amplitude of variation. They are classified into population I and II Cepheids, Miras and semi-regular long-period variables. The population I Cepheids are associated with the spiral arms, while the central concentration of the Miras and long-period variables varies noticeably, the stars with brighter (and shorter) variations being much more centrally concentrated. A crucial role in the microlensing experiment is played by the asymmetry signal. It was initially assumed that the variable stars would ...

PHOTOMETRIC VARIABILITY IN KEPLER TARGET STARS: THE SUN AMONG STARS-A FIRST LOOK

International Nuclear Information System (INIS)

Basri, Gibor; Walkowicz, Lucianne M.; Batalha, Natalie; Jenkins, Jon; Borucki, William J.; Koch, David; Caldwell, Doug; Gilliland, Ronald L.; Dupree, Andrea K.; Latham, David W.; Meibom, Soeren; Howell, Steve; Brown, Tim

2010-01-01

The Kepler mission provides an exciting opportunity to study the light curves of stars with unprecedented precision and continuity of coverage. This is the first look at a large sample of stars with photometric data of a quality that has heretofore been only available for our Sun. It provides the first opportunity to compare the irradiance variations of our Sun to a large cohort of stars ranging from very similar to rather different stellar properties, at a wide variety of ages. Although Kepler data are in an early phase of maturity, and we only analyze the first month of coverage, it is sufficient to garner the first meaningful measurements of our Sun's variability in the context of a large cohort of main-sequence stars in the solar neighborhood. We find that nearly half of the full sample is more active than the active Sun, although most of them are not more than twice as active. The active fraction is closer to a third for the stars most similar to the Sun, and rises to well more than half for stars cooler than mid-K spectral types.

NEAR-INFRARED PERIODIC AND OTHER VARIABLE FIELD STARS IN THE FIELD OF THE CYGNUS OB7 STAR-FORMING REGION

Energy Technology Data Exchange (ETDEWEB)

Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin A. [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

2013-04-15

We present a subset of the results of a three-season, 124 night, near-infrared monitoring campaign of the dark clouds Lynds 1003 and Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we focus on the field star population. Using three seasons of UKIRT J, H, and K-band observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. After excluding known disk-bearing stars we identify 149 variables-1.6% of the sample. Of these, about 60 are strictly periodic, with periods predominantly <2 days. We conclude this group is dominated by eclipsing binaries. A few stars have long period signals of between 20 and 60 days. About 25 stars have weak modulated signals, but it was not clear if these were periodic. Some of the stars in this group may be diskless young stellar objects with relatively large variability due to cool starspots. The remaining {approx}60 stars showed variations which appear to be purely stochastic.

An explicit formula for a star product with separation of variables

OpenAIRE

Karabegov, Alexander

2011-01-01

For a star product with separation of variables * on a pseudo-Kaehler manifold we give a simple closed formula of the total symbol of the left star multiplication operator L_f by a given function f. The formula for the star product f * g can be immediately recovered from the total symbol of L_f.

Variable Stars Observed in the Galactic Disk by AST3-1 from Dome A, Antarctica

Energy Technology Data Exchange (ETDEWEB)

Wang, Lingzhi; Ma, Bin; Hu, Yi; Liu, Qiang; Shang, Zhaohui [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Li, Gang; Fu, Jianning [Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Wang, Lifan; Cui, Xiangqun; Du, Fujia; Gong, Xuefei; Li, Xiaoyan; Li, Zhengyang; Yuan, Xiangyan; Zhou, Jilin [Chinese Center for Antarctic Astronomy, Nanjing 210008 (China); Ashley, Michael C. B. [School of Physics, University of New South Wales, NSW 2052 (Australia); Pennypacker, Carl R. [Center for Astrophysics, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); York, Donald G., E-mail: wanglingzhi@bao.ac.cn [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)

2017-03-01

AST3-1 is the second-generation wide-field optical photometric telescope dedicated to time-domain astronomy at Dome A, Antarctica. Here, we present the results of an i -band images survey from AST3-1 toward one Galactic disk field. Based on time-series photometry of 92,583 stars, 560 variable stars were detected with i magnitude ≤16.5 mag during eight days of observations; 339 of these are previously unknown variables. We tentatively classify the 560 variables as 285 eclipsing binaries (EW, EB, and EA), 27 pulsating variable stars ( δ Scuti, γ Doradus, δ Cephei variable, and RR Lyrae stars), and 248 other types of variables (unclassified periodic, multiperiodic, and aperiodic variable stars). Of the eclipsing binaries, 34 show O’Connell effects. One of the aperiodic variables shows a plateau light curve and another variable shows a secondary maximum after peak brightness. We also detected a complex binary system with an RS CVn-like light-curve morphology; this object is being followed-up spectroscopically using the Gemini South telescope.

Faint (and bright variable stars in the satellites of the Milky Way

Directory of Open Access Journals (Sweden)

Vivas A. Katherina

2017-01-01

Full Text Available I describe two ongoing projects related with variable stars in the satellites of the MilkyWay. In the first project, we are searching for dwarf Cepheid stars (a.k.a δ Scuti and/or SX Phe in some of the classical dwarf spheroidal galaxies. Our goal is to characterize the population of these variable stars under different environments (age, metallicity in order to study their use as standard candles in systems for which the metallicity is not necessarily known. In the second project we search for RR Lyrae stars in the new ultra-faint satellite galaxies that have been discovered around the Milky Way in recent years.

The variable stars of NGC 1866

International Nuclear Information System (INIS)

Welch, D.L.; Cote, P.; Fischer, P.; Mateo, M.; Madore, B.F.

1991-01-01

A search has been conducted for new variables in the LMC cluster NGC 1866 using new multiepoch CCD photometry. Eight previously unknown Cepheid variables, most near the cluster core, are found. Of the new variables reported by Storm et al. (188), only six of 10 appear to be Cepheids and one of these is not a member. Periods and mean magnitudes and colors for sufficiently uncrowded variables are reported, as is one red giant variable of long period and one Cepheid which is a single-lined spectroscopic binary with a velocity semiamplitude greater than or equal to 10.5 km/s. The variation of light-curve amplitude with position in the instability strip is reported along with an apparently nonvariable star, which is a radial velocity member, in the strip. A true distance modulus of 18.57 + or - 0.01 mag is obtained for the cluster. 36 refs

ERUPTIVE VARIABLE STARS AND OUTFLOWS IN SERPENS NW

Energy Technology Data Exchange (ETDEWEB)

Hodapp, Klaus W. [Institute for Astronomy, University of Hawaii, 640 N. Aohoku Place, Hilo, HI 96720 (United States); Chini, Rolf; Watermann, Ramon; Lemke, Roland, E-mail: hodapp@ifa.hawaii.edu [Ruhr Universitaet Bochum, Astronomisches Institut, Universitaetsstrasse 150, D-44801 Bochum (Germany)

2012-01-01

We study the outflow activity, photometric variability, and morphology of three very young stellar objects in the Serpens NW star-forming region: OO Serpentis, EC 37 (V370 Ser), and EC 53 (V371 Ser). High spatial resolution Keck/NIRC2 laser guide star adaptive optics images obtained in 2007 and 2009 in broadband K and in a narrowband filter centered on the 1-0 S(1) emission line of H{sub 2} allow us to identify the outflows from all three objects. We also present new, seeing-limited data on the photometric evolution of the OO Ser reflection nebula and re-analyze previously published data. We find that OO Ser declined in brightness from its outburst peak in 1995 to about 2003, but that this decline has recently stopped and actually reversed itself in some areas of the reflection nebula. The morphology and proper motions of the shock fronts MHO 2218 near EC 37 suggest that they all originate in EC 37 and that this is an outflow seen nearly along its axis. We identify an H{sub 2} jet emerging from the cometary nebula EC 53. The star illuminating EC 53 is periodically variable with a period of 543 days and has a close-by, non-variable companion at a projected distance of 92 AU. We argue that the periodic variability is the result of accretion instabilities triggered by another very close, not directly observable, binary companion and that EC 53 can be understood in the model of a multiple system developing into a hierarchical configuration.

New Galactic Candidate Luminous Blue Variables and Wolf-Rayet Stars

Science.gov (United States)

Stringfellow, Guy S.; Gvaramadze, Vasilii V.; Beletsky, Yuri; Kniazev, Alexei Y.

2012-04-01

We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 μm) and GLIMPSE (8 μm) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of this class.

Binarity and Variable Stars in the Open Cluster NGC 2126

Science.gov (United States)

Chehlaeh, Nareemas; Mkrtichian, David; Kim, Seung-Lee; Lampens, Patricia; Komonjinda, Siramas; Kusakin, Anatoly; Glazunova, Ljudmila

2018-04-01

We present the results of an analysis of photometric time-series observations for NGC 2126 acquired at the Thai National Observatory (TNO) in Thailand and the Mount Lemmon Optical Astronomy Observatory (LOAO) in USA during the years 2004, 2013 and 2015. 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. NGC 2126 is an intermediate-age open cluster which has a population of stars inside the δ Scuti instability strip. Several variable stars are reported including three eclipsing binary stars, one of which is an eclipsing binary star with a pulsating component (V551 Aur). The Wilson-Devinney technique was used to analyze its light curves and to determine a new set of the system’s parameters. A frequency analysis of the eclipse-subtracted light curve was also performed. Eclipsing binaries which are members of open clusters are capable of delivering strong constraints on the cluster’s properties which are in turn useful for a pulsational analysis of their pulsating components. 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 2126. The new Devasthal Optical Telescope, suitably equipped, could in principle do this.

On a New Technique for Discovering Variable Stars

Directory of Open Access Journals (Sweden)

Mironov A. V.

2003-12-01

Full Text Available A technique for discovering variable stars based on the calculation of the correlation coefficients is proposed. Applications of the technique are shown on the results of numerical experiments and on the Hipparcos photometric data.

A photometric study of the giant red variable stars with small amplitudes

International Nuclear Information System (INIS)

Wisse, P.N.J.

1979-01-01

Three colour UBV observations of southern semiregular and irregular red variable stars are presented. Well covered light and colour curves have been obtained for ca. 40 stars. In most cases the observations span more than one cycle. A short description is given for all individual variables. The observations are accurate enough to reveal many minor irregularities in the light variation. The SRb and Lb variables define a narrow curved strip in the (U-B) - (B-V) diagram. This strip has been called the Locus of Red Variables (LRV). The (U-B) of the variables is about 0.5 magnitudes bluer than that of the K III giants. (Auth.)

Examining the infrared variable star population discovered in the Small Magellanic Cloud using the SAGE-SMC survey

International Nuclear Information System (INIS)

Polsdofer, Elizabeth; Marengo, M.; Seale, J.; Sewiło, M.; Vijh, U. P.; Terrazas, M.; Meixner, M.

2015-01-01

We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud” (SAGE-SMC) and the “Spitzer Survey of the Small Magellanic Cloud” (S 3 MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer’s InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 μm bands, and the Multiband Imaging Photometer for Spitzer 24 μm band. An error-weighted flux difference between each pair of three epochs (“variability index”) is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ∼2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.

Examining the infrared variable star population discovered in the Small Magellanic Cloud using the SAGE-SMC survey

Energy Technology Data Exchange (ETDEWEB)

Polsdofer, Elizabeth; Marengo, M. [Iowa State University, Department of Physics and Astronomy, 12 Physics Hall, Ames, Iowa 50011 (United States); Seale, J.; Sewiło, M. [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Vijh, U. P.; Terrazas, M. [Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606 (United States); Meixner, M., E-mail: empolsdofer@gmail.com [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)

2015-02-01

We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud” (SAGE-SMC) and the “Spitzer Survey of the Small Magellanic Cloud” (S{sup 3}MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer’s InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 μm bands, and the Multiband Imaging Photometer for Spitzer 24 μm band. An error-weighted flux difference between each pair of three epochs (“variability index”) is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ∼2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.

Variable stars in the Leo A dwarf galaxy (DDO 69)

Science.gov (United States)

Hoessel, John G.; Saha, A.; Krist, John; Danielson, G. Edward

1994-01-01

Observations of the Leo A dwarf galaxy, obtained over the period from 1980 to 1991 are reported. Forty two separate Charge Coupled Devices (CCD) frames were searched for variable stars. A total of 14 suspected variables were found, 9 had sufficient coverage for period determination, and 5 had Cepheid light curves. Four of these stars fit well on a P-L relation and yield a distance modulus, after correction for Galactic foreground extinction, of m-M = 26.74. This corresponds to a distance of 2.2 Mpc, placing Leo A near the Local Group zero-velocity surface.

The Search for New Luminous Blue Variable Stars: Near-Infrared Spectroscopy of Stars With 24 micron Shells

Science.gov (United States)

Stringfellow, Guy; Gvaramadze, Vasilii

2010-02-01

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.g. Ofpe/WN9, WNL) phases in the life of very massive stars. 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.

Identification and period investigation of pulsation variable star UY Camelopardalis, an RR Lyrae star in binary system

Science.gov (United States)

Li, Lin-Jia; Qian, Sheng-Bang; Voloshina, Irina; Metlov, Vladimir G.; Zhu, Li-Ying; Liao, Wen-Ping

2018-06-01

We present photometric measurements of the short period variable star UY Cam, which has been classified as a δ Scuti or c-type RR Lyrae (RRc) variable in different catalogs. Based on the analyses on Fourier coefficients and (NUV - V)0, we find that UY Cam is probably an RRc star. We obtain 58 new times of light maximum for UY Cam based on several sky surveys and our observations. Combining these with the times of light maximum in literature, a total of 154 times of light maximum are used to analyze the O - C diagram of UY Cam. The results show that the O - C pattern can be described by a downward parabolic component with a rate of -6.86 ± 0.47 × 10-11 d d-1, and a cyclic variation with a period of 65.7 ± 2.4 yr. We suppose these components are caused by the stellar evolution and the light travel time effect (LiTE) of a companion in elliptical orbit, respectively. By calculation, the minimum mass of the potential companion is about 0.17 M⊙, and its mass should be less than or equal to the pulsation primary star when the inclination i > 22.5°D. Therefore, the companion should be a low-mass star, like a late-type main-sequence star or a white dwarf. Due to the unique property of UY Cam, we suggest that more observations and studies on UY Cam and other RRc stars are needed to check the nature of these stars, including the pulsations and binarities.

New helium spectrum variable and a new helium-rich star

International Nuclear Information System (INIS)

Walborn, N.R.

1974-01-01

HD 184927, known previously as a helium-rich star, has been found to have a variable helium spectrum; the equivalent widths of five He I lines are larger by an average of 46 percent on a 1974 spectrogram than on one obtained with the same equipment in 1970. HD 186205 has been found to be a new, pronounced helium-rich star. (auth)

Infrared properties of Mira-type variables and other cool stars as determined from JHKL photometry

Energy Technology Data Exchange (ETDEWEB)

Feast, M W; Robertson, B S.C.; Catchpole, R M; Evans, T L; Glass, I S; Carter, B S [South African Astronomical Observatory, Cape

1982-11-01

Extensive infrared photometry of Me(Mira) variables and of C, S, SC and related stars is used to establish two-colour diagrams and period-colour relations. The characteristic areas in these plots occupied by the different classes of objects are delineated. The main aim is to provide a norm with which other stars (e.g. red variables in the Galactic Center and in the Magellanic Clouds and peculiar stars) can be compared. The (J-H) versus period relation offers a method for determining the interstellar reddenings of Me variables. The strong concentration to the longer periods of Miras which are OH masers is probably due primarily to the fact that in the sample surveyed, these stars also have the brightest apparent bolometric magnitudes. Period-amplitude plots are shown for Me variables. The Mira components in symbiotic stars are found to have exceptionally large amplitudes.

Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

Science.gov (United States)

Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

2014-02-01

The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

Variable stars classification based on photometric data from the "Pi of the Sky" project

Science.gov (United States)

Majczyna, A.; Nalezyty, M.; Siudek, M.; Malek, K.; Barnacka, A.; Mankiewicz, L.; Żarnecki, A. F.

2009-06-01

We present the first few steps of creation the second edition of the variable stars catalogue, based on the "Pi of the Sky" data, collected during two years 2006-2007. We have chosen - 3000 variable star candidates from about 1.5 million objects.

The Kepler characterization of the variability among A- and F-type stars. I. General overview

DEFF Research Database (Denmark)

Uytterhoeven, K.; Moya, A.; Grigahcène, A.

2011-01-01

candidate A-F type stars, and observationally investigate the relation between γ Doradus (γ Dor), δ Scuti (δ Sct), and hybrid stars. Methods: We compile a database of physical parameters for the sample stars from the literature and new ground-based observations. We analyse the Kepler light curve of each...... no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much higher fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical...... constructed variables, "efficiency" and "energy", as a means to explore the relation between γ Dor and δ Sct stars. Conclusions: Our results suggest a revision of the current observational instability strips of δ Sct and γ Dor stars and imply an investigation of pulsation mechanisms to supplement the κ...

A Search for Circumstellar Gas-Disk Variability in F-type Stars

Science.gov (United States)

Adkins, Ally; Montgomery, Sharon Lynn; Welsh, Barry

2018-01-01

Over the past six years, short-term (night-to-night) variability in the CaII K-line (3933Å) absorption has been detected towards 22 rapidly-rotating A-type stars, all but four of them discovered by us. Most of these stars are young (age McDonald Observatory) during June 2017. The appearance or absence of similar short-lived, Doppler-shifted absorption in F-type stars serves as a test of our understanding of the underlying phenomena.

Evolution of compact stars and dark dynamical variables

Energy Technology Data Exchange (ETDEWEB)

Bhatti, M.Z.; Yousaf, Z. [University of the Punjab, Department of Mathematics, Lahore (Pakistan); Ilyas, M. [University of the Punjab, Centre for High Energy Physics, Lahore (Pakistan)

2017-10-15

This work aims to explore the dark dynamical effects of the f(R, T) modified gravity theory on the dynamics of a compact celestial star. We have taken the interior geometry of a spherical star which is filled with an imperfect fluid distribution. The modified field equations are explored by taking a particular form of the f(R, T) model, i.e. f(R, T) = f{sub 1}(R) + f{sub 2}(R)f{sub 3}(T). These equations are utilized to formulate the well-known structure scalars under the dark dynamical effects of this higher-order gravity theory. Also, with the help of these scalar variables, the evolution equations for expansion and shear are formulated. The whole analysis is made under the condition of a constant R and T. We found a crucial significance of dark source terms and dynamical variables on the evolution and density inhomogeneity of compact objects. (orig.)

SpecDB: The AAVSO’s Public Repository for Spectra of Variable Stars

Science.gov (United States)

Kafka, Stella; Weaver, John; Silvis, George; Beck, Sara

2018-01-01

SpecDB is the American Association of Variable Star Observers (AAVSO) spectral database. Accessible to any astronomer with the capability to perform spectroscopy, SpecDB provides an unprecedented scientific opportunity for amateur and professional astronomers around the globe. Backed by the Variable Star Index, one of the most utilized variable star catalogs, SpecDB is expected to become one of the world leading databases of its kind. Once verified by a team of expert spectroscopists, an observer can upload spectra of variable stars target easily and efficiently. Uploaded spectra can then be searched for, previewed, and downloaded for inclusion in publications. Close community development and involvement will ensure a user-friendly and versatile database, compatible with the needs of 21st century astrophysics. Observations of 1D spectra are submitted as FITS files. All spectra are required to be preprocessed for wavelength calibration and dark subtraction; Bias and flat are strongly recommended. First time observers are required to submit a spectrum of a standard (non-variable) star to be checked for errors in technique or equipment. Regardless of user validation, FITS headers must include several value cards detailing the observation, as well as information regarding the observer, equipment, and observing site in accordance with existing AAVSO records. This enforces consistency and provides necessary details for follow up analysis. Requirements are provided to users in a comprehensive guidebook and accompanying technical manual. Upon submission, FITS headers are automatically checked for errors and any anomalies are immediately fed back to the user. Successful candidates can then submit at will, including multiple simultaneous submissions. All published observations can be searched and interactively previewed. Community involvement will be enhanced by an associated forum where users can discuss observation techniques and suggest improvements to the database.

Spectral Variability of the UXOR Star RR Tau Over 2.5 Magnitudes in V

Science.gov (United States)

Rodgers, B.; Wooden, D. H.; Grinin, V. P.; Shakhovskoy, D.

2000-12-01

We present moderate resolution optical spectra of the highly variable Herbig Ae star RR Tau over 12 epochs spanning 2.5 magnitudes in V. The data cover most of the optical spectrum from the CaII K line in the blue to the CaII infrared triplet in the far red. Using contemporaneous photometric measurements from two sources, we have reliable estimates of the visual magnitude of the system at each spectral epoch. We find some spectral activity to be closely correlated with photometric variability, while other features are remarkably stable. Significant variability is common in the cores of Hα and Hβ , but is not well correlated with photometric variability. On the other hand, the wings (Δ v>400km/s) of the Balmer lines are quite stable, showing no change in spectral type when compared to Kurucz line profiles. This, along with the constant equivalent width seen in several weak metal lines, suggest that the physical conditions of the underlying continuum source are not changing significantly, despite a factor of ten change in brightness. In contrast, strong low-ionization permitted lines, such as FeII, CaII and NaI, are seen in deep absorption when the star is bright (V <= 12), but disappear during photometric minima to reveal weak emission lines. These absorption lines are not being filled in by the emission but rather are physically disappearing from the system. This could occur, for example, if an obscuring screen moved between the continuum source and the absorbing gas. The [OI]6300 line, a common wind diagnostic, is seen in emission at all epochs, with flux which is roughly constant except increasing slightly when the system is faint. We discuss these data in the context of different scenarios for the photometric variability and find them to be more consistent with the obscuration hypothesis, than changing accretion luminosity. This work is part of the dissertation research of B. Rodgers, which has been funded in large part by a NASA Graduate Student Research

Model atmospheres with periodic shocks. [pulsations and mass loss in variable stars

Science.gov (United States)

Bowen, G. H.

1989-01-01

The pulsation of a long-period variable star generates shock waves which dramatically affect the structure of the star's atmosphere and produce conditions that lead to rapid mass loss. Numerical modeling of atmospheres with periodic shocks is being pursued to study the processes involved and the evolutionary consequences for the stars. It is characteristic of these complex dynamical systems that most effects result from the interaction of various time-dependent processes.

DISCOVERY OF A WOLF-RAYET STAR THROUGH DETECTION OF ITS PHOTOMETRIC VARIABILITY

Energy Technology Data Exchange (ETDEWEB)

Littlefield, Colin [Law School, University of Notre Dame, Notre Dame, IN 46556 (United States); Garnavich, Peter; McClelland, Colin; Rettig, Terrence [Physics Department, University of Notre Dame, Notre Dame, IN 46556 (United States); Marion, G. H. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Vinko, Jozsef [Department of Optics, University of Szeged (Hungary); Wheeler, J. Craig [Astronomy Department, University of Texas, Austin, TX 78712 (United States)

2012-06-15

We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 A, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 A line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocular Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B - V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 {+-} 0.3 kpc.

DISCOVERY OF A WOLF-RAYET STAR THROUGH DETECTION OF ITS PHOTOMETRIC VARIABILITY

International Nuclear Information System (INIS)

Littlefield, Colin; Garnavich, Peter; McClelland, Colin; Rettig, Terrence; Marion, G. H.; Vinkó, József; Wheeler, J. Craig

2012-01-01

We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 Å, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 Å line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocular Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B – V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 ± 0.3 kpc.

IMPROVED VARIABLE STAR SEARCH IN LARGE PHOTOMETRIC DATA SETS: NEW VARIABLES IN CoRoT FIELD LRa02 DETECTED BY BEST II

International Nuclear Information System (INIS)

Fruth, T.; Cabrera, J.; Csizmadia, Sz.; Eigmüller, P.; Erikson, A.; Kirste, S.; Pasternacki, T.; Rauer, H.; Titz-Weider, R.; Kabath, P.; Chini, R.; Lemke, R.; Murphy, M.

2012-01-01

The CoRoT field LRa02 has been observed with the Berlin Exoplanet Search Telescope II (BEST II) during the southern summer 2007/2008. A first analysis of stellar variability led to the publication of 345 newly discovered variable stars. Now, a deeper analysis of this data set was used to optimize the variability search procedure. Several methods and parameters have been tested in order to improve the selection process compared to the widely used J index for variability ranking. This paper describes an empirical approach to treat systematic trends in photometric data based upon the analysis of variance statistics that can significantly decrease the rate of false detections. Finally, the process of reanalysis and method improvement has virtually doubled the number of variable stars compared to the first analysis by Kabath et al. A supplementary catalog of 272 previously unknown periodic variables plus 52 stars with suspected variability is presented. Improved ephemerides are given for 19 known variables in the field. In addition, the BEST II results are compared with CoRoT data and its automatic variability classification.

The ISLAnds Project. III. Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies

Science.gov (United States)

Martínez-Vázquez, Clara E.; Monelli, Matteo; Bernard, Edouard J.; Gallart, Carme; Stetson, Peter B.; Skillman, Evan D.; Bono, Giuseppe; Cassisi, Santi; Fiorentino, Giuliana; McQuinn, Kristen B. W.; Cole, Andrew A.; McConnachie, Alan W.; Martin, Nicolas F.; Dolphin, Andrew E.; Boylan-Kolchin, Michael; Aparicio, Antonio; Hidalgo, Sebastian L.; Weisz, Daniel R.

2017-12-01

We present a census of variable stars in six M31 dwarf spheroidal satellites observed with the Hubble Space Telescope. We detect 870 RR Lyrae (RRL) stars in the fields of And I (296), II (251), III (111), XV (117), XVI (8), and XXVIII (87). We also detect a total of 15 Anomalous Cepheids, three eclipsing binaries, and seven field RRL stars compatible with being members of the M31 halo or the Giant Stellar Stream. We derive robust and homogeneous distances to the six galaxies using different methods based on the properties of the RRL stars. Working with the up-to-date set of Period-Wesenheit (I, B-I) relations published by Marconi et al., we obtain distance moduli of μ 0 = [24.49, 24.16, 24.36, 24.42, 23.70, 24.43] mag (respectively), with systematic uncertainties of 0.08 mag and statistical uncertainties <0.11 mag. We have considered an enlarged sample of 16 M31 satellites with published variability studies, and compared their pulsational observables (e.g., periods and amplitudes) with those of 15 Milky Way satellites for which similar data are available. The properties of the (strictly old) RRL in both satellite systems do not show any significant difference. In particular, we found a strikingly similar correlation between the mean period distribution of the fundamental RRL pulsators (RRab) and the mean metallicities of the galaxies. This indicates that the old RRL progenitors were similar at the early stage in the two environments, suggesting very similar characteristics for the earliest stages of evolution of both satellite systems. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 13028 and 13739.

Star Products with Separation of Variables Admitting a Smooth Extension

Science.gov (United States)

Karabegov, Alexander

2012-08-01

Given a complex manifold M with an open dense subset Ω endowed with a pseudo-Kähler form ω which cannot be smoothly extended to a larger open subset, we consider various examples where the corresponding Kähler-Poisson structure and a star product with separation of variables on (Ω, ω) admit smooth extensions to M. We give a simple criterion of the existence of a smooth extension of a star product and apply it to these examples.

Star products with separation of variables admitting a smooth extension

OpenAIRE

Karabegov, Alexander

2010-01-01

Given a complex manifold $M$ with an open dense subset $\\Omega$ endowed with a pseudo-Kaehler form $\\omega$ which cannot be smoothly extended to a larger open subset, we consider various examples where the corresponding Kaehler-Poisson structure and a star product with separation of variables on $(\\Omega, \\omega)$ admit smooth extensions to $M$. We suggest a simple criterion of the existence of a smooth extension of a star product and apply it to these examples.

Eight to 14 μm spectral monitoring of long period variable stars with GLADYS.

Science.gov (United States)

Levan, P. D.; Sloan, G.; Grasdalen, G.

The authors describe an ongoing program of spectral monitoring of long period variable stars using GLADYS, a long slit prism spectrometer that employs a 58x62 pixel Si:Ga detector array. The goal is to compare the equivalent widths of the SiC emission features in carbon-rich circumstellar shells, and the silicate emission features in oxygen-rich circumstellar stars, obtained over different phases of the continuum variability cycle. Spectra of long period variables and low amplitude variables recently obtained on the Wyoming Infrared Observatory 2.3 m telescope are presented.

The UK Infrared Telescope M33 monitoring project - I. Variable red giant stars in the central square kiloparsec

Science.gov (United States)

Javadi, Atefeh; van Loon, Jacco Th.; Mirtorabi, Mohammad Taghi

2011-02-01

We have conducted a near-infrared monitoring campaign at the UK Infrared Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive data set was obtained in the K band with the UIST instrument for the central 4 × 4 arcmin2 (1 kpc2) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18 398 stars in this region; of these, 812 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the variability survey and the photometric catalogue - which is made publicly available at the Centre de Données astronomiques de Strasbourg - and discuss the properties of the variable stars. The most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey.

VARIABLE STARS IN THE LARGE MAGELLANIC CLOUD GLOBULAR CLUSTER NGC 2257. I. RESULTS BASED ON 2007-2008 B, V PHOTOMETRY

International Nuclear Information System (INIS)

Nemec, James M.; Walker, Alistair; Jeon, Young-Beom

2009-01-01

The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ∼20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9 m telescope on 14 nights in 2007 December and 2008 January. New period searches have been made using two independent algorithms (CLEAN, Period04); the resultant periods of most of the stars are consistent with the pulsation periods derived previously, and where there are discrepancies these have been resolved. For the B and V light curves, accurate Fourier coefficients and parameters are given. Six new variable stars have been discovered (V45-50), including a bright candidate long-period variable star showing secondary oscillations (V45) and two anomalously bright RRc stars (V48 and V50), which are shown to be brightened and reddened by nearby red giant stars. Also discovered among the previously known variable stars are three double-mode RR Lyrae stars (V8, V16, and V34) and several Blazhko variables. Archival Hubble Space Telescope images and the photometry by Johnson et al. have been used to define better the properties of the most crowded variable stars. The total number of cluster variable stars now stands at forty-seven: 23 RRab stars, four of which show Blazhko amplitude variations; 20 RRc stars, one showing clear Blazhko variations and another showing possible Blazhko variations; the three RRd stars, all having the dominant period ∼0.36 day and period ratios P 1 /P 0 ∼0.7450; and an LPV star located near the tip of the red giant branch. A comparison of the RRd stars with those in other environments shows them to be most similar to those in IC4499.

Revisiting Caroline Furness's An Introduction to the Study of Variable Stars on its Centenary (Poster abstract)

Science.gov (United States)

Larsen, K.

2016-06-01

(Abstract only) A century and one month ago (October 1915) Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, published An Introduction to the Study of Variable Stars. 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 and as a manual explaining how they should be observed and the resulting data analyzed. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World's Fair in Chicago. 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. Furness's work is a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. This presentation will analyze both Furness's book and its reception in the scientific community, and draw parallels to current advice given to beginning variable star observers.

Black hole variability and the star formation-active galactic nucleus connection: Do all star-forming galaxies host an active galactic nucleus?

International Nuclear Information System (INIS)

Hickox, Ryan C.; Chen, Chien-Ting J.; Civano, Francesca M.; Hainline, Kevin N.; Mullaney, James R.; Alexander, David M.; Goulding, Andy D.

2014-01-01

We investigate the effect of active galactic nucleus (AGN) variability on the observed connection between star formation and black hole accretion in extragalactic surveys. Recent studies have reported relatively weak correlations between observed AGN luminosities and the properties of AGN hosts, which has been interpreted to imply that there is no direct connection between AGN activity and star formation. However, AGNs may be expected to vary significantly on a wide range of timescales (from hours to Myr) that are far shorter than the typical timescale for star formation (≳100 Myr). This variability can have important consequences for observed correlations. We present a simple model in which all star-forming galaxies host an AGN when averaged over ∼100 Myr timescales, with long-term average AGN accretion rates that are perfectly correlated with the star formation rate (SFR). We show that reasonable prescriptions for AGN variability reproduce the observed weak correlations between SFR and L AGN in typical AGN host galaxies, as well as the general trends in the observed AGN luminosity functions, merger fractions, and measurements of the average AGN luminosity as a function of SFR. These results imply that there may be a tight connection between AGN activity and SFR over galaxy evolution timescales, and that the apparent similarities in rest-frame colors, merger rates, and clustering of AGNs compared to 'inactive' galaxies may be due primarily to AGN variability. The results provide motivation for future deep, wide extragalactic surveys that can measure the distribution of AGN accretion rates as a function of SFR.

Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

Science.gov (United States)

Nielsen, Martin Bo

2017-03-01

The Sun and other stars are known to oscillate. Through the study of small perturbations to the frequencies of these oscillations the rotation of the deep interior can be inferred. However, thus far the internal rotation of other Sun-like stars is unknown. The NASA Kepler mission has observed a multitude of Sun-like stars over a period of four years. This has provided high-quality photometric data that can be used to study the rotation of stars with two different techniques: asteroseismology and surface activity. Asteroseismology provides a means of measuring rotation in the stellar interior, while photometric variability from magnetically active regions are sensitive to rotation at the stellar surface. The combination of these two methods can be used to constrain the radial differential rotation in Sun-like stars. First, we developed an automated method for measuring the rotation of stars using surface variability. This method was initially applied to the entire Kepler catalog, out of which we detected signatures of rotation in 12,000 stars across the main sequence, providing robust estimates of the surface rotation rates and the associated errors. Second, we performed an asteroseismic analysis of six Sun-like stars, where we were able to measure the rotational splitting as a function of frequency in the p-mode envelope. This was done by dividing the oscillation spectrum into individual segments, and fitting a model independently to each segment. We found that the measured splittings were all consistent with a constant value, indicating little differential rotation. Third, we compared the asteroseismic rotation rates of five Sun-like stars to their surface rotation rates. We found that the values were in good agreement, again indicating little differential rotation between the regions where the two methods are most sensitive. Finally, we discuss how the surface rotation rates may be used as a prior on the seismic envelope rotation rate in a double-zone model

SWSex Stars, Old Novae, and the Evolution of Cataclysmic Variables

Directory of Open Access Journals (Sweden)

L. Schmidtobreick

2015-02-01

Full Text Available The population of cataclysmic variables with orbital periods right above the period gap are dominated by systems with extremely high mass transfer rates, the so-called SW Sextantis stars. On the other hand, some old novae in this period range which are expected to show high mass transfer rate instead show photometric and/or spectroscopic resemblance to low mass transfer systems like dwarf novae. We discuss them as candidates for so-called hibernating systems, CVs that changed their mass transfer behaviour due to a previously experienced nova outburst. This paper is designed to provide input for further research and discussion as the results as such are still very preliminary.

A NEW CENSUS OF THE VARIABLE STAR POPULATION IN THE GLOBULAR CLUSTER NGC 2419

International Nuclear Information System (INIS)

Di Criscienzo, M.; Greco, C.; Ripepi, V.; Dall' Ora, M.; Marconi, M.; Musella, I.; Clementini, G.; Federici, L.; Di Fabrizio, L.

2011-01-01

We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two δ Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification. The pulsation properties of the RR Lyrae variables are close to those of Oosterhoff type II clusters, consistent with the low metal abundance and the cluster horizontal branch morphology, disfavoring (but not totally ruling out) an extragalactic hypothesis for the origin of NGC 2419. The observed properties of RR Lyrae and SX Phoenicis stars are used to estimate the cluster reddening and distance, using a number of different methods. Our final value is μ 0 (NGC 2419) = 19.71 ± 0.08 mag (D = 87.5 ± 3.3 kpc), with E(B - V) = 0.08 ± 0.01 mag, [Fe/H] = -2.1 dex on the Zinn and West metallicity scale, and a value of M V that sets μ 0 (LMC) = 18.52 mag. This value is in good agreement with the most recent literature estimates of the distance to NGC 2419.

Development of a Mailing List on Variable Stars, VSNET

Science.gov (United States)

Nogami, D.; Kato, T.; Baba, H.; Kunjaya, C.

Various usages of the Internet have been developed and made remarkable progress these years, which is now dramatically changing the style of astronomical study. Among those, the maing list is thought to be most useful to study of unpredictable objects for the characteristics, especially rapidness and equality. We started a mailing list (VSNET) on variable stars, mainly on cataclysmic variables and supernovae, in 1994 July for mutual exchange of information and ideas between astronomers including professionals and amateurs. Up to now, the various articles have been distributed, for example, calls for follow up observations of transient objects discovered in the UV or X-ray region, calls for ground-based observations simultaneous with ones by the space telescopes, discoveries of supernovae, alert notices of outbursts in long dormant dwarf novae (EG Cnc, AL Com, UZ Boo, HT Cas, etc), and so on. You can get long-term light curves of variable stars drawn using VSNET data on the VSNET web pages http://www.kusastro.kyoto-u.ac.jp/vsnet/. The archives of VSNET mails are available via VSNET web pages and anonymous ftp ftp://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/Mail/. If you have any questions and suggestions on VSNET, please feel free to contact us (vsnet-adm@kusastro.kyoto-u.ac.jp).

VARIABLE STARS IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY URSA MAJOR I

Energy Technology Data Exchange (ETDEWEB)

Garofalo, Alessia; Moretti, Maria Ida [Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Cusano, Felice; Clementini, Gisella [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Ripepi, Vincenzo; Dall' Ora, Massimo; Coppola, Giuseppina; Musella, Ilaria; Marconi, Marcella, E-mail: alessia.garofalo@studio.unibo.it, E-mail: fcusano@na.astro.it, E-mail: gisella.clementini@oabo.inaf.it, E-mail: ripepi@na.astro.it, E-mail: dallora@na.astro.it, E-mail: imoretti@na.astro.it, E-mail: coppola@na.astro.it, E-mail: ilaria@na.astro.it, E-mail: marcella@na.astro.it [INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy)

2013-04-10

We have performed the first study of the variable star population of Ursa Major I (UMa I), an ultra-faint dwarf satellite recently discovered around the Milky Way (MW) by the Sloan Digital Sky Survey. Combining time series observations in the B and V bands from four different telescopes, we have identified seven RR Lyrae stars in UMa I, of which five are fundamental-mode (RRab) and two are first-overtone pulsators (RRc). Our V, B - V color-magnitude diagram of UMa I reaches V {approx} 23 mag (at a signal-to-noise ratio of {approx}6) and shows features typical of a single old stellar population. The mean pulsation period of the RRab stars (P{sub ab}) = 0.628, {sigma} = 0.071 days (or (P{sub ab}) = 0.599, {sigma} = 0.032 days, if V4, the longest period and brightest variable, is discarded) and the position on the period-amplitude diagram suggest an Oosterhoff-intermediate classification for the galaxy. The RR Lyrae stars trace the galaxy horizontal branch (HB) at an average apparent magnitude of (V(RR)) = 20.43 {+-} 0.02 mag (average on six stars and discarding V4), giving in turn a distance modulus for UMa I of (m - M){sub 0} = 19.94 {+-} 0.13 mag, distance d = 97.3{sup +6.0}{sub -5.7} kpc, in the scale where the distance modulus of the Large Magellanic Cloud is 18.5 {+-} 0.1 mag. Isodensity contours of UMa I red giants and HB stars (including the RR Lyrae stars identified in this study) show that the galaxy has an S-shaped structure, which is likely caused by the tidal interaction with the MW. Photometric metallicities were derived for six of the UMa I RR Lyrae stars from the parameters of the Fourier decomposition of the V-band light curves, leading to an average metal abundance of [Fe/H] = -2.29 dex ({sigma} = 0.06 dex, average on six stars) on the Carretta et al. metallicity scale.

A SYSTEMATIC SEARCH FOR COROTATING INTERACTION REGIONS IN APPARENTLY SINGLE GALACTIC WOLF-RAYET STARS. II. A GLOBAL VIEW OF THE WIND VARIABILITY

International Nuclear Information System (INIS)

Chene, A.-N.; St-Louis, N.

2011-01-01

This study is the second part of a survey searching for large-scale spectroscopic variability in apparently single Wolf-Rayet (WR) stars. In a previous paper (Paper I), we described and characterized the spectroscopic variability level of 25 WR stars observable from the northern hemisphere and found 3 new candidates presenting large-scale wind variability, potentially originating from large-scale structures named corotating interaction regions (CIRs). In this second paper, we discuss an additional 39 stars observable from the southern hemisphere. For each star in our sample, we obtained 4-5 high-resolution spectra with a signal-to-noise ratio of ∼100 and determined its variability level using the approach described in Paper I. In total, 10 new stars are found to show large-scale spectral variability of which 7 present CIR-type changes (WR 8, WR 44, WR55, WR 58, WR 61, WR 63, WR 100). Of the remaining stars, 20 were found to show small-amplitude changes and 9 were found to show no spectral variability as far as can be concluded from the data on hand. Also, we discuss the spectroscopic variability level of all single galactic WR stars that are brighter than v ∼ 12.5, and some WR stars with 12.5 < v ≤ 13.5, i.e., all the stars presented in our two papers and four more stars for which spectra have already been published in the literature. We find that 23/68 stars (33.8%) present large-scale variability, but only 12/54 stars (∼22.1%) are potentially of CIR type. Also, we find that 31/68 stars (45.6%) only show small-scale variability, most likely due to clumping in the wind. Finally, no spectral variability is detected based on the data on hand for 14/68 (20.6%) stars. Interestingly, the variability with the highest amplitude also has the widest mean velocity dispersion.

ACTIVE LEARNING TO OVERCOME SAMPLE SELECTION BIAS: APPLICATION TO PHOTOMETRIC VARIABLE STAR CLASSIFICATION

Energy Technology Data Exchange (ETDEWEB)

Richards, Joseph W.; Starr, Dan L.; Miller, Adam A.; Bloom, Joshua S.; Butler, Nathaniel R.; Berian James, J. [Astronomy Department, University of California, Berkeley, CA 94720-7450 (United States); Brink, Henrik [Dark Cosmology Centre, Juliane Maries Vej 30, 2100 Copenhagen O (Denmark); Long, James P.; Rice, John, E-mail: jwrichar@stat.berkeley.edu [Statistics Department, University of California, Berkeley, CA 94720-7450 (United States)

2012-01-10

Despite the great promise of machine-learning algorithms to classify and predict astrophysical parameters for the vast numbers of astrophysical sources and transients observed in large-scale surveys, the peculiarities of the training data often manifest as strongly biased predictions on the data of interest. Typically, training sets are derived from historical surveys of brighter, more nearby objects than those from more extensive, deeper surveys (testing data). This sample selection bias can cause catastrophic errors in predictions on the testing data because (1) standard assumptions for machine-learned model selection procedures break down and (2) dense regions of testing space might be completely devoid of training data. We explore possible remedies to sample selection bias, including importance weighting, co-training, and active learning (AL). We argue that AL-where the data whose inclusion in the training set would most improve predictions on the testing set are queried for manual follow-up-is an effective approach and is appropriate for many astronomical applications. For a variable star classification problem on a well-studied set of stars from Hipparcos and Optical Gravitational Lensing Experiment, AL is the optimal method in terms of error rate on the testing data, beating the off-the-shelf classifier by 3.4% and the other proposed methods by at least 3.0%. To aid with manual labeling of variable stars, we developed a Web interface which allows for easy light curve visualization and querying of external databases. Finally, we apply AL to classify variable stars in the All Sky Automated Survey, finding dramatic improvement in our agreement with the ASAS Catalog of Variable Stars, from 65.5% to 79.5%, and a significant increase in the classifier's average confidence for the testing set, from 14.6% to 42.9%, after a few AL iterations.

ACTIVE LEARNING TO OVERCOME SAMPLE SELECTION BIAS: APPLICATION TO PHOTOMETRIC VARIABLE STAR CLASSIFICATION

International Nuclear Information System (INIS)

Richards, Joseph W.; Starr, Dan L.; Miller, Adam A.; Bloom, Joshua S.; Butler, Nathaniel R.; Berian James, J.; Brink, Henrik; Long, James P.; Rice, John

2012-01-01

Despite the great promise of machine-learning algorithms to classify and predict astrophysical parameters for the vast numbers of astrophysical sources and transients observed in large-scale surveys, the peculiarities of the training data often manifest as strongly biased predictions on the data of interest. Typically, training sets are derived from historical surveys of brighter, more nearby objects than those from more extensive, deeper surveys (testing data). This sample selection bias can cause catastrophic errors in predictions on the testing data because (1) standard assumptions for machine-learned model selection procedures break down and (2) dense regions of testing space might be completely devoid of training data. We explore possible remedies to sample selection bias, including importance weighting, co-training, and active learning (AL). We argue that AL—where the data whose inclusion in the training set would most improve predictions on the testing set are queried for manual follow-up—is an effective approach and is appropriate for many astronomical applications. For a variable star classification problem on a well-studied set of stars from Hipparcos and Optical Gravitational Lensing Experiment, AL is the optimal method in terms of error rate on the testing data, beating the off-the-shelf classifier by 3.4% and the other proposed methods by at least 3.0%. To aid with manual labeling of variable stars, we developed a Web interface which allows for easy light curve visualization and querying of external databases. Finally, we apply AL to classify variable stars in the All Sky Automated Survey, finding dramatic improvement in our agreement with the ASAS Catalog of Variable Stars, from 65.5% to 79.5%, and a significant increase in the classifier's average confidence for the testing set, from 14.6% to 42.9%, after a few AL iterations.

Active Learning to Overcome Sample Selection Bias: Application to Photometric Variable Star Classification

Science.gov (United States)

Richards, Joseph W.; Starr, Dan L.; Brink, Henrik; Miller, Adam A.; Bloom, Joshua S.; Butler, Nathaniel R.; James, J. Berian; Long, James P.; Rice, John

2012-01-01

Despite the great promise of machine-learning algorithms to classify and predict astrophysical parameters for the vast numbers of astrophysical sources and transients observed in large-scale surveys, the peculiarities of the training data often manifest as strongly biased predictions on the data of interest. Typically, training sets are derived from historical surveys of brighter, more nearby objects than those from more extensive, deeper surveys (testing data). This sample selection bias can cause catastrophic errors in predictions on the testing data because (1) standard assumptions for machine-learned model selection procedures break down and (2) dense regions of testing space might be completely devoid of training data. We explore possible remedies to sample selection bias, including importance weighting, co-training, and active learning (AL). We argue that AL—where the data whose inclusion in the training set would most improve predictions on the testing set are queried for manual follow-up—is an effective approach and is appropriate for many astronomical applications. For a variable star classification problem on a well-studied set of stars from Hipparcos and Optical Gravitational Lensing Experiment, AL is the optimal method in terms of error rate on the testing data, beating the off-the-shelf classifier by 3.4% and the other proposed methods by at least 3.0%. To aid with manual labeling of variable stars, we developed a Web interface which allows for easy light curve visualization and querying of external databases. Finally, we apply AL to classify variable stars in the All Sky Automated Survey, finding dramatic improvement in our agreement with the ASAS Catalog of Variable Stars, from 65.5% to 79.5%, and a significant increase in the classifier's average confidence for the testing set, from 14.6% to 42.9%, after a few AL iterations.

Understanding of variability properties in very low mass stars and brown dwarfs

Science.gov (United States)

Mondal, Soumen; Ghosh, Samrat; Khata, Dhrimadri; Joshi, Santosh; Das, Ramkrishna

2018-04-01

We report on photometric variability studies of a L3.5 brown dwarf 2MASS J00361617+1821104 (2M0036+18) in the field and of four young brown dwarfs in the star-forming region IC 348. From muti-epoch observations, we found significant periodic variability in 2M0036+18 with a period of 2.66 ± 0.55 hours on one occasion while it seemed to be non-variable on three other occasions. An evolving dust cloud might cause such a scenario. Among four young brown dwarfs of IC 348 in the spectral range M7.25 - M8, one brown dwarf 2MASS J03443921+3208138 shows significant variability. The K-band spectra (2.0-2.4 μm) of nine very low mass stars (M1 - M9 V) are used to characterize the water band index (H20-K2). We found that it is strongly correlated with the surface temperature of M dwarfs.

Chromospheric activity of periodic variable stars (including eclipsing binaries) observed in DR2 LAMOST stellar spectral survey

Science.gov (United States)

Zhang, Liyun; Lu, Hongpeng; Han, Xianming L.; Jiang, Linyan; Li, Zhongmu; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Cao, Zihuang

2018-05-01

The LAMOST spectral survey provides a rich databases for studying stellar spectroscopic properties and chromospheric activity. We cross-matched a total of 105,287 periodic variable stars from several photometric surveys and databases (CSS, LINEAR, Kepler, a recently updated eclipsing star catalogue, ASAS, NSVS, some part of SuperWASP survey, variable stars from the Tsinghua University-NAOC Transient Survey, and other objects from some new references) with four million stellar spectra published in the LAMOST data release 2 (DR2). We found 15,955 spectra for 11,469 stars (including 5398 eclipsing binaries). We calculated their equivalent widths (EWs) of their Hα, Hβ, Hγ, Hδ and Caii H lines. Using the Hα line EW, we found 447 spectra with emission above continuum for a total of 316 stars (178 eclipsing binaries). We identified 86 active stars (including 44 eclipsing binaries) with repeated LAMOST spectra. A total of 68 stars (including 34 eclipsing binaries) show chromospheric activity variability. We also found LAMOST spectra of 12 cataclysmic variables, five of which show chromospheric activity variability. We also made photometric follow-up studies of three short period targets (DY CVn, HAT-192-0001481, and LAMOST J164933.24+141255.0) using the Xinglong 60-cm telescope and the SARA 90-cm and 1-m telescopes, and obtained new BVRI CCD light curves. We analyzed these light curves and obtained orbital and starspot parameters. We detected the first flare event with a huge brightness increase of more than about 1.5 magnitudes in R filter in LAMOST J164933.24+141255.0.

Observations on the variability of linear polarization in late-type dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Huovelin, J.; Linnaluoto, S.; Tuominen, I.; Virtanen, H.

1989-04-01

Broadband (UBV) linear polarimetric observations of a sample of late-type (F7-K5) dwarfs are reported. The observations include ten stars and extend over a maximum of 20 nights. Seven stars show significant temporal variability of polarization, which could be interpreted as rotational modulation due to slowly varying magnetic regions. Magnetic intensification in saturated Zeeman sensitive absorption lines is suggested as the dominant effect connecting linear polarization with magnetic activity in the most active single late-type dwarfs, while the wavelength dependence in the less active stars could also be due to a combination of Rayleigh and Thomson scattering.

Clustering-based Feature Learning on Variable Stars

Science.gov (United States)

Mackenzie, Cristóbal; Pichara, Karim; Protopapas, Pavlos

2016-04-01

The success of automatic classification of variable stars depends strongly on the lightcurve representation. Usually, lightcurves are represented as a vector of many descriptors designed by astronomers called features. These descriptors are expensive in terms of computing, require substantial research effort to develop, and do not guarantee a good classification. Today, lightcurve representation is not entirely automatic; algorithms must be designed and manually tuned up for every survey. The amounts of data that will be generated in the future mean astronomers must develop scalable and automated analysis pipelines. In this work we present a feature learning algorithm designed for variable objects. Our method works by extracting a large number of lightcurve subsequences from a given set, which are then clustered to find common local patterns in the time series. Representatives of these common patterns are then used to transform lightcurves of a labeled set into a new representation that can be used to train a classifier. The proposed algorithm learns the features from both labeled and unlabeled lightcurves, overcoming the bias using only labeled data. We test our method on data sets from the Massive Compact Halo Object survey and the Optical Gravitational Lensing Experiment; the results show that our classification performance is as good as and in some cases better than the performance achieved using traditional statistical features, while the computational cost is significantly lower. With these promising results, we believe that our method constitutes a significant step toward the automation of the lightcurve classification pipeline.

CLUSTERING-BASED FEATURE LEARNING ON VARIABLE STARS

International Nuclear Information System (INIS)

Mackenzie, Cristóbal; Pichara, Karim; Protopapas, Pavlos

2016-01-01

The success of automatic classification of variable stars depends strongly on the lightcurve representation. Usually, lightcurves are represented as a vector of many descriptors designed by astronomers called features. These descriptors are expensive in terms of computing, require substantial research effort to develop, and do not guarantee a good classification. Today, lightcurve representation is not entirely automatic; algorithms must be designed and manually tuned up for every survey. The amounts of data that will be generated in the future mean astronomers must develop scalable and automated analysis pipelines. In this work we present a feature learning algorithm designed for variable objects. Our method works by extracting a large number of lightcurve subsequences from a given set, which are then clustered to find common local patterns in the time series. Representatives of these common patterns are then used to transform lightcurves of a labeled set into a new representation that can be used to train a classifier. The proposed algorithm learns the features from both labeled and unlabeled lightcurves, overcoming the bias using only labeled data. We test our method on data sets from the Massive Compact Halo Object survey and the Optical Gravitational Lensing Experiment; the results show that our classification performance is as good as and in some cases better than the performance achieved using traditional statistical features, while the computational cost is significantly lower. With these promising results, we believe that our method constitutes a significant step toward the automation of the lightcurve classification pipeline

CLUSTERING-BASED FEATURE LEARNING ON VARIABLE STARS

Energy Technology Data Exchange (ETDEWEB)

Mackenzie, Cristóbal; Pichara, Karim [Computer Science Department, Pontificia Universidad Católica de Chile, Santiago (Chile); Protopapas, Pavlos [Institute for Applied Computational Science, Harvard University, Cambridge, MA (United States)

2016-04-01

The success of automatic classification of variable stars depends strongly on the lightcurve representation. Usually, lightcurves are represented as a vector of many descriptors designed by astronomers called features. These descriptors are expensive in terms of computing, require substantial research effort to develop, and do not guarantee a good classification. Today, lightcurve representation is not entirely automatic; algorithms must be designed and manually tuned up for every survey. The amounts of data that will be generated in the future mean astronomers must develop scalable and automated analysis pipelines. In this work we present a feature learning algorithm designed for variable objects. Our method works by extracting a large number of lightcurve subsequences from a given set, which are then clustered to find common local patterns in the time series. Representatives of these common patterns are then used to transform lightcurves of a labeled set into a new representation that can be used to train a classifier. The proposed algorithm learns the features from both labeled and unlabeled lightcurves, overcoming the bias using only labeled data. We test our method on data sets from the Massive Compact Halo Object survey and the Optical Gravitational Lensing Experiment; the results show that our classification performance is as good as and in some cases better than the performance achieved using traditional statistical features, while the computational cost is significantly lower. With these promising results, we believe that our method constitutes a significant step toward the automation of the lightcurve classification pipeline.

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

Energy Technology Data Exchange (ETDEWEB)

Miles, Brittany E. [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu [School of Earth and Space Exploration, Arizona State University, 781 S Terrace Road, Tempe, AZ 85281 (United States)

2017-08-01

The ultraviolet (UV) light from a host star influences a planet’s atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope . These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer ( GALEX ) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771–2831 Å) and far-ultraviolet (FUV; 1344–1786 Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.

Thirteen-colour photometry of Be stars

Energy Technology Data Exchange (ETDEWEB)

Alvarez, M; Schuster, W J [Universidad Nacional Autonoma de Mexico, Mexico City. Inst. de Astronomia

1981-01-01

Thirteen-colour photometry made at the San Pedro Martir Observatory in Baja California, for a number of spectroscopically variable Be and shell stars is presented. Several of these stars also show photometric variability in the ultraviolet and/or infrared over a time base of two to three years. We analyze the more interesting stars in terms of colour-colour diagrams, colour excesses, spectral characteristics and changes in their energy distributions. Prospects for future research are discussed.

Thirteen-colour photometry of Be stars

International Nuclear Information System (INIS)

Alvarez, M.; Schuster, W.J.

1981-01-01

Thirteen-colour photometry made at the San Pedro Martir Observatory in Baja California, for a number of spectroscopically variable Be and shell stars is presented. Several of these stars also show photometric variability in the ultraviolet and/or infrared over a time base of two to three years. We analyze the more interesting stars in terms of colour-colour diagrams, colour excesses, spectral characteristics and changes in their energy distributions. Prospects for future research are discussed. (author)

Smearing model and restoration of star image under conditions of variable angular velocity and long exposure time.

Science.gov (United States)

Sun, Ting; Xing, Fei; You, Zheng; Wang, Xiaochu; Li, Bin

2014-03-10

The star tracker is one of the most promising attitude measurement devices widely used in spacecraft for its high accuracy. High dynamic performance is becoming its major restriction, and requires immediate focus and promotion. A star image restoration approach based on the motion degradation model of variable angular velocity is proposed in this paper. This method can overcome the problem of energy dispersion and signal to noise ratio (SNR) decrease resulting from the smearing of the star spot, thus preventing failed extraction and decreased star centroid accuracy. Simulations and laboratory experiments are conducted to verify the proposed methods. The restoration results demonstrate that the described method can recover the star spot from a long motion trail to the shape of Gaussian distribution under the conditions of variable angular velocity and long exposure time. The energy of the star spot can be concentrated to ensure high SNR and high position accuracy. These features are crucial to the subsequent star extraction and the whole performance of the star tracker.

Variable blue straggler stars in NGC 5466

International Nuclear Information System (INIS)

Harris, H.C.; Mateo, M.; Olszewski, E.W.; Nemec, J.M.

1990-01-01

Nine variable blue stragglers have been found in the globular cluster NGC 5466. The six dwarf Cepheids in this cluster coexist in the instability strip with other nonvariable stars. The three eclipsing binaries are among the hottest of the blue stragglers. The hypothesis is discussed that all blue stragglers in this cluster have undergone mass transfer in close binaries. Under this hypothesis, rotation and spin-down play important roles in controlling the evolution of blue stragglers in old clusters and in affecting some of their observational properties. 14 refs

VizieR Online Data Catalog: Abundances of 8 RR Lyrae subclass C variable stars (Govea+, 2014)

Science.gov (United States)

Govea, J.; Gomez, T.; Preston, G. W.; Sneden, C.

2016-02-01

We chose 10 candidate RR Lyrae variable stars of subclass c (RRc) stars for spectroscopic observation. Many of these stars were first identified as RRc variables by the All Sky Automated Survey (ASAS) of Pojmanski 2003 (cat. II/264). The target star list included ASAS 144154-0324.7 and ASAS 204440-2402.7. But our spectroscopic study suggest that these two stars are probably W UMa binaries instead of RR Lyrae stars Our spectra were obtained with the echelle spectrograph of the du Pont 2.5m telescope at the Las Campanas Observatory. Four observing runs during 2009-2010 were partly devoted to this project. The spectrograph was used with the 1.5*4'' entrance slit, which translates to a resolving power of R=λ/Δλ~27000 at the MgI b lines near 5180Å. The total continuous wavelength coverage of the spectra was 3500-9000Å. (6 data files).

Variable stars in the VVV globular clusters. I. 2MASS-GC 02 and Terzan 10

Energy Technology Data Exchange (ETDEWEB)

Alonso-García, Javier; Dékány, István; Catelan, Márcio; Ramos, Rodrigo Contreras; Gran, Felipe; Leyton, Paul; Minniti, Dante [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile); Amigo, Pía, E-mail: jalonso@astro.puc.cl, E-mail: idekany@astro.puc.cl, E-mail: mcatelan@astro.puc.cl, E-mail: rcontrer@astro.puc.cl, E-mail: fgran@astro.puc.cl, E-mail: pia.amigo@uv.cl, E-mail: pleyton@astro.puc.cl, E-mail: dante@astrofisica.cl [Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)

2015-03-01

The VISTA Variables in the Vía Láctea (VVV) ESO Public Survey is opening a new window to study inner Galactic globular clusters (GCs) using their variable stars. These GCs have been neglected in the past due to the difficulties caused by the presence of elevated extinction and high field stellar densities in their lines of sight. However, the discovery and study of any present variables in these clusters, especially RR Lyrae stars, can help to greatly improve the accuracy of their physical parameters. It can also help to shed some light on the questions raised by the intriguing Oosterhoff dichotomy in the Galactic GC system. In a series of papers we plan to explore variable stars in the GCs falling inside the field of the VVV survey. In this first paper, we search for and study the variables present in two highly reddened, moderately metal-poor, faint, inner Galactic GCs: 2MASS-GC 02 and Terzan 10. We report the discovery of sizable populations of RR Lyrae stars in both GCs. We use near-infrared period–luminosity relations to determine the color excess of each RR Lyrae star, from which we obtain both accurate distances to the GCs and the ratios of the selective-to-total extinction in their directions. We find the extinction toward both clusters to be elevated, non-standard, and highly differential. We also find both clusters to be closer to the Galactic center than previously thought, with Terzan 10 being on the far side of the Galactic bulge. Finally, we discuss their Oosterhoff properties, and conclude that both clusters stand out from the dichotomy followed by most Galactic GCs.

Stargazing: an integrative conceptual review, theoretical reconciliation, and extension for star employee research.

Science.gov (United States)

Call, Matthew L; Nyberg, Anthony J; Thatcher, Sherry M B

2015-05-01

Stars--employees with disproportionately high and prolonged (a) performance, (b) visibility, and (c) relevant social capital--have garnered attention in economics, sociology, and management. However, star research is often isolated within these research disciplines. Thus, 3 distinct star research streams are evolving, each disconnected from the others and each bringing siloed theoretical perspectives, terms, and assumptions. A conceptual review of these perspectives reveals a focus on the expost effects that stars exert in organizations with little explanation of who a star is and how one becomes a star. To synthesize the stars literature across these 3 disciplines, we apply psychological theories, specifically motivation theories, to create an integrative framework for stars research. Thus, we present a unified stars definition and extend theory on the making, managing, and mobility of stars. We extend research about how and why employees may be motivated to become stars, how best to manage stars and their relationships with colleagues, and how to motivate star retention. We then outline directions for future research. (c) 2015 APA, all rights reserved.

CzeV - The Czech Variable Star Catalogue

Czech Academy of Sciences Publication Activity Database

Skarka, M.; Mašek, Martin; Brát, L.; Cagaš, P.A.; Juryšek, J.; Hoňková, K.; Zejda, M.; Šmelcer, L.; Jelínek, Martin; Lomoz, F.; Tylšar, M.; Trnka, J.; Pejcha, O.; Pintr, P.; Lehký, M.; Janík, J.; Červinka, L.; Tylšar, M.; Přibík, V.; Motl, D.; Walter, F.; Zasche, P.; Koss, K.; Hájek, P.; Bílek, F.; Liška, J.; Kučáková, H.; Bodnár, F.; Beránek, J.; Šafář, J.; Moudrá, M.; Oršulák, M.; Pintr, M.; Sobotka, P.; Dřevěný, R.; Juráňová, A.; Polák, J.; Polster, J.; Onderková, K.; Smolka, M.; Auer, R.F.; Kocián, R.; Hladík, B.; Cagaš, P.; Greš, A.; Müller, D.; Čapková, H.; Kyselý, Jan; Hornoch, Kamil; Truparová, S.; Timko, L.; Brož, M.; Bílek, Michal; Šebela, P.; Hanžl, D.; Žampachová, E.; Secká, J.; Pravec, Petr; Mrňák, P.; Svoboda, P.; Ehrenberger, R.; Novotný, F.; Poddaný, S.; Prudil, Z.; Kuchťák, B.; Štegner, D.

2017-01-01

Roč. 185, Sep (2017), s. 1-42 ISSN 1801-5964 R&D Projects: GA MŠk LM2015038; GA MŠk LG15014; GA MŠk LM2015046; GA MŠk LTT17006 EU Projects: European Commission(XE) 283783 - GLORIA Grant - others:OP VVV - AUGER-CZ(XE) CZ.02.1.01/0.0/0.0/16_013/0001402; OP VVV - CTAO-CZ(XE) CZ.02.1.01/0.0/0.0/16_013/0001403 Institutional support: RVO:68378271 ; RVO:67985815 ; RVO:68378289 Keywords : variable stars * eclipsing binaries Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science)

A search for time variability and its possible regularities in linear polarization of Be stars

International Nuclear Information System (INIS)

Huang, L.; Guo, Z.H.; Hsu, J.C.; Huang, L.

1989-01-01

Linear polarization measurements are presented for 14 Be stars obtained at McDonald Observatory during four observing runs from June to November of 1983. Methods of observation and data reduction are described. Seven of eight program stars which were observed on six or more nights exhibited obvious polarimetric variations on time-scales of days or months. The incidence is estimated as 50% and may be as high as 93%. No connection can be found between polarimetric variability and rapid periodic light or spectroscopic variability for our stars. Ultra-rapid variability on time-scale of minutes was searched for with negative results. In all cases the position angles also show variations indicating that the axis of symmetry of the circumstellar envelope changes its orientation in space. For the Be binary CX Dra the variations in polarization seems to have a period which is just half of the orbital period

Multi-Epoch Hubble Space Telescope Observations of IZw18 : Characterization of Variable Stars at Ultra-Low Metallicities

NARCIS (Netherlands)

Fiorentino, G.; Ramos, R. Contreras; Clementini, G.; Marconi, M.; Musella, I.; Aloisi, A.; Annibali, F.; Saha, A.; Tosi, M.; van der Marel, R. P.

2010-01-01

Variable stars have been identified for the first time in the very metal-poor blue compact dwarf galaxy IZw18, using deep multi-band (F606W, F814W) time-series photometry obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope. We detected 34 candidate variable stars in the

High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability

Energy Technology Data Exchange (ETDEWEB)

Chojnowski, S. Drew; Holtzman, Jon A. [Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059 (United States); Wisniewski, John P. [Department of Physics and Astronomy, The University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019 (United States); Whelan, David G. [Department of Physics, Austin College, 900 N. Grand Avenue, Sherman, TX 75090 (United States); Labadie-Bartz, Jonathan; Pepper, Joshua [Department of Physics, Lehigh University, Bethlehem, PA 18015 (United States); Fernandes, Marcelo Borges [Observatório Nacional, Rua General José Cristino 77, 20921-400, São Cristovão, Rio de Janeiro (Brazil); Lin, Chien-Cheng [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road Shanghai 200030 (China); Majewski, Steven R. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Stringfellow, Guy S. [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, Colorado 80309-0389 (United States); Mennickent, Ronald E.; Tang, Baitian [Departamento de Astronomía, Universidad de Concepción, Concepción (Chile); Roman-Lopes, Alexandre [Departamento de Física, Facultad de Ciencias, Universidad de La Serena, Cisternas 1200, La Serena (Chile); Hearty, Fred R. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Zasowski, Gail [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States)

2017-04-01

We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.

High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability

International Nuclear Information System (INIS)

Chojnowski, S. Drew; Holtzman, Jon A.; Wisniewski, John P.; Whelan, David G.; Labadie-Bartz, Jonathan; Pepper, Joshua; Fernandes, Marcelo Borges; Lin, Chien-Cheng; Majewski, Steven R.; Stringfellow, Guy S.; Mennickent, Ronald E.; Tang, Baitian; Roman-Lopes, Alexandre; Hearty, Fred R.; Zasowski, Gail

2017-01-01

We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.

Spectrophotometry of peculiar B and A stars. XVIII - The helium rich variable stars HR 1890, Sigma Orionis E, and HD 37776

Science.gov (United States)

Adelman, S. J.; Pyper, D. M.

1985-01-01

Optical region spectrophotometry at 3300-7850 A has been obtained for three helium rich stars, HR 1890, Sigma Ori E, and HD 37776, of the Orion OB1 Association. New uvby-beta photometry of HR 1890 and HD 37776 as well as published data are also used to investigate the variability of these stars. A new period of 1.53862 days was determined for HD 37776. For all three stars H-beta varies in antiphase with strong He I lines. The spectrophotometric bandpass containing the strong He I line at 4471 A varies in phase with the R index of Pedersen and Thomsen (1977). Evidence is found for weak absorption features which appear to be an extension of the 5200 A feature seen in cooler CP stars.

Variable Stars in (Not Only) Dwarf Galaxies : Key Tools to Constrain Distances and Stellar Content

NARCIS (Netherlands)

Fiorentino, G.; Koleva, M; Prugniel, P; Vauglin,

2011-01-01

The important role of Cepheid and RR Lyrae variable stars and what they teach us about dwarf galaxies is discussed. Despite ever improving star formation histories of Local Group dwarf galaxies uncertainties remain, in particular in the identification and characterisation of the oldest stellar

Field #3 of the Palomar-Groningen Survey; 1, Variable stars at the edge of the Sagittarius dwarf galaxy

NARCIS (Netherlands)

Schultheis, M.

1996-01-01

Submitted to: Astron. Astrophys. Abstract: A catalogue is presented with variable (RR Lyrae, semiregular and Mira) stars located inside field #3 of the Palomar-Groningen Survey, at the outer edge of the Sagittarius dwarf galaxy. One of the semiregular variables is a carbon star, comparable with

The STAR Data Reporting Guidelines for Clinical High Altitude Research.

Science.gov (United States)

Brodmann Maeder, Monika; Brugger, Hermann; Pun, Matiram; Strapazzon, Giacomo; Dal Cappello, Tomas; Maggiorini, Marco; Hackett, Peter; Bärtsch, Peter; Swenson, Erik R; Zafren, Ken

2018-03-01

Brodmann Maeder, Monika, Hermann Brugger, Matiram Pun, Giacomo Strapazzon, Tomas Dal Cappello, Marco Maggiorini, Peter Hackett, Peter Baärtsch, Erik R. Swenson, Ken Zafren (STAR Core Group), and the STAR Delphi Expert Group. The STARdata reporting guidelines for clinical high altitude research. High AltMedBiol. 19:7-14, 2018. The goal of the STAR (STrengthening Altitude Research) initiative was to produce a uniform set of key elements for research and reporting in clinical high-altitude (HA) medicine. The STAR initiative was inspired by research on treatment of cardiac arrest, in which the establishment of the Utstein Style, a uniform data reporting protocol, substantially contributed to improving data reporting and subsequently the quality of scientific evidence. The STAR core group used the Delphi method, in which a group of experts reaches a consensus over multiple rounds using a formal method. We selected experts in the field of clinical HA medicine based on their scientific credentials and identified an initial set of parameters for evaluation by the experts. Of 51 experts in HA research who were identified initially, 21 experts completed both rounds. The experts identified 42 key parameters in 5 categories (setting, individual factors, acute mountain sickness and HA cerebral edema, HA pulmonary edema, and treatment) that were considered essential for research and reporting in clinical HA research. An additional 47 supplemental parameters were identified that should be reported depending on the nature of the research. The STAR initiative, using the Delphi method, identified a set of key parameters essential for research and reporting in clinical HA medicine.

An investigation of the photometric variability of confirmed and candidate Galactic Be stars using ASAS-3 data

Science.gov (United States)

Bernhard, Klaus; Otero, Sebastián; Hümmerich, Stefan; Kaltcheva, Nadejda; Paunzen, Ernst; Bohlsen, Terry

2018-05-01

We present an investigation of a large sample of confirmed (N=233) and candidate (N=54) Galactic classical Be stars (mean V magnitude range of 6.4 to 12.6 mag), with the main aim of characterizing their photometric variability. Our sample stars were preselected among early-type variables using light curve morphology criteria. Spectroscopic information was gleaned from the literature, and archival and newly-acquired spectra. Photometric variability was analyzed using archival ASAS-3 time series data. To enable a comparison of results, we have largely adopted the methodology of Labadie-Bartz et al. (2017), who carried out a similar investigation based on KELT data. Complex photometric variations were established in most stars: outbursts on different time-scales (in 73±5 % of stars), long-term variations (36±6 %), periodic variations on intermediate time-scales (1±1 %) and short-term periodic variations (6±3 %). 24±6 % of the outbursting stars exhibit (semi)periodic outbursts. We close the apparent void of rare outbursters reported by Labadie-Bartz et al. (2017), and show that Be stars with infrequent outbursts are not rare. While we do not find a significant difference in the percentage of stars showing outbursts among early-type, mid-type and late-type Be stars, we show that early-type Be stars exhibit much more frequent outbursts. We have measured rising and falling times for well-covered and well-defined outbursts. Nearly all outburst events are characterized by falling times that exceed the rising times. No differences were found between early-, mid- and late-type stars; a single non-linear function adequately describes the ratio of falling time to rising time across all spectral subtypes, with the ratio being larger for short events.

INFRARED PERIOD-LUMINOSITY RELATIONS OF EVOLVED VARIABLE STARS IN THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Riebel, David; Meixner, Margaret; Fraser, Oliver; Srinivasan, Sundar; Cook, Kem; Vijh, Uma

2010-01-01

We combine variability information from the MAssive Compact Halo Objects survey of the Large Magellanic Cloud with infrared photometry from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution survey to create a data set of ∼30,000 variable red sources. We photometrically classify these sources as being on the first ascent of the red giant branch, or as being in one of three stages along the asymptotic giant branch (AGB): oxygen-rich, carbon-rich, or highly reddened with indeterminate chemistry ('extreme' AGB candidates). We present linear period-luminosity (P-L) relationships for these sources using eight separate infrared bands (J, H, K s , 3.6, 4.5, 5.8, 8.0, and 24 μm) as proxies for the luminosity. We find that the wavelength dependence of the slope of the P-L relationship is different for different photometrically determined classes of AGB stars. Stars photometrically classified as O-rich show the least variation of slope with wavelength, while dust enshrouded extreme AGB stars show a pronounced trend toward steeper slopes with increasing wavelength. We find that O-rich AGB stars pulsating in the fundamental mode obey a period-magnitude relation with a slope of -3.41 ± 0.04 when magnitude is measured in the 3.6 μm band, in contrast to C-rich AGB stars, which obey a relation of slope -3.77 ± 0.05.

A search for β Cephei variable stars in the Magellanic Clouds: motivation and first results for the LMC

International Nuclear Information System (INIS)

Sterken, C.; Jerzykiewicz, M.

1988-01-01

Motivation for starting a programme of detecting and investigating β Cephei variables in the Magellanic Clouds is given. Differential photoelectric observations are then reported of six LMC stars which fall in the instability strip defined by the galactic β Cephei variables. Three programme stars are found to exhibit short-term brightness variations. One of them, showing a sinusoidal light-curve with an amplitude (half-range) equal to 0.0070 ± 0.0011 mag and a period equal to about 5 hr, is a promising β Cephei candidate. In the case of the other two variable programme stars, the interpretation of the results is less straightforward. The remaining three programme stars are shown to be constant on a short time-scale, two to within ± 0.010 mag, and one to within ± 0.005 magn. (author)

Peculiar variable star R Aquarii and its jet

Energy Technology Data Exchange (ETDEWEB)

Kafatos, M; Michalitsianos, A G [National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center

1982-08-05

The formation of a jet from the central star in the symbiotic variable R Aquarii is discussed and it is suggested that it is the result of supercritical accretion of mass transferred from the cool 387-day period Mira to the hot companion in a highly elliptical orbit. Ancient Japanese astronomical records suggest a nova outburst in AD930 may be associated with R Aquarii which formed the outer extended nebulosity. It is considered that the jet may help explain the outbursts of this object as well as the excitation of the R Aquarii nebula.

An ultraviolet study of B[e] stars: evidence for pulsations, luminous blue variable type variations and processes in envelopes

Science.gov (United States)

Krtičková, I.; Krtička, J.

2018-06-01

Stars that exhibit a B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including the presence of Balmer lines in emission, forbidden lines and strong infrared excess due to dust. Observations of emission lines indicate illumination by an ultraviolet ionizing source, which is key to understanding the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from the Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and the correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including light absorption by the disc, pulsations, luminous blue variable type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is present not only in the disc but also above its plane. The flux and line variability is consistent with a two-component model of a circumstellar environment composed of a dense disc and an ionized envelope. Observations of B[e] supergiants show that many of these stars have nearly the same luminosity, about 1.9 × 105 L⊙, and similar effective temperatures.

BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. IV. THE CENTRAL STARS OF HaTr 4 AND Hf 2-2

Energy Technology Data Exchange (ETDEWEB)

Hillwig, Todd C.; Schaub, S. C. [Department of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383 (United States); Bond, Howard E. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Frew, David J. [Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong); Bodman, Eva H. L., E-mail: todd.hillwig@valpo.edu [Southeastern Association for Research in Astronomy (SARA) (United States)

2016-08-01

We explore the photometrically variable central stars of the planetary nebulae HaTr 4 and Hf 2-2. Both have been classified as close binary star systems previously based on their light curves alone. Here, we present additional arguments and data confirming the identification of both as close binaries with an irradiated cool companion to the hot central star. We include updated light curves, orbital periods, and preliminary binary modeling for both systems. We also identify for the first time the central star of HaTr 4 as an eclipsing binary. Neither system has been well studied in the past, but we utilize the small amount of existing data to limit possible binary parameters, including system inclination. These parameters are then compared to nebular parameters to further our knowledge of the relationship between binary central stars of planetary nebulae and nebular shaping and ejection.

Spectral Variability of the Herbig Ae/Be Star HD 37806

Science.gov (United States)

Pogodin, M. A.; Pavlovskiy, S. E.; Kozlova, O. V.; Beskrovnaya, N. G.; Alekseev, I. Yu.; Valyavin, G. G.

2018-03-01

Results are reported from a spectroscopic study of the Herbig Ae/Be star HD 37806 from 2009 through 2017 using high resolution spectrographs at the Crimean Astrophysical Observatory and the OAN SPM Observatory in Mexico. 72 spectra of this object near the Hα, Hβ, HeI 5876 and D NaI lines are analyzed. The following results were obtained: 1. The type of spectral profile of the Hα line can change from P Cyg III to double emission and vice versa over a time scale on the order of a month. 2. Narrow absorption components are observed in the profiles of the Hα and D NaI lines with radial velocities that vary over a characteristic time on the order of a day. 3. On some days, the profiles of the Hβ, HeI 5876, and D NaI lines show signs of accretion of matter to the star with a characteristic lifetime of a few days. A possible interpretation of these phenomena was considered. The transformation of the Hα profile may be related to a change in the outer latitudinal width of the boundary of the wind zone. The narrow variable absorption lines may be caused by the rotation of local azimuthal inhomogeneities in the wind zone owing to the interaction of the disk with the star's magnetosphere in a propeller regime. Several current theoretical papers that predict the formation of similar inhomogeneous wind structures were examined. It is suggested that the episodes with signs of accretion in the spectral line profiles cannot be a consequence of the modulation of these profiles by the star's rotation but are more likely caused by sudden, brief changes in the accretion rate. These spectral observations of HD 37806 should be continued in a search for cyclical variability in the spectral parameters in order to identify direct signs of magnetospheric accretion and detect possible binary behavior in this object.

Unravelling the role of SW Sextantis stars in the evolution of cataclysmic variables

Science.gov (United States)

Araujo-Betancor, Sofia; Gansicke, Boris; Long, Knox; Rodriguez-Gil, Pablo

2005-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assessment of their evolutionary state is illusionary. There is one particular behavior of the SW Sex stars that can allow us to overcome this problem: SW Sex stars exhibit low states during which accretion onto the white dwarf decreases or shuts off completely. Only during this rare occasions we can directly observe the white dwarf and the donor star in these systems, and measurements of the white dwarf temperature, spectral type of the donor, mass and distance to the system can be carried out. With this aim in mind, we have set up a long-term monitoring of a group of five SW Sex stars using the 1.3 m telescope at CTIO. Here we propose to activate follow-up TOOs to obtain optical spectra of the low states to accurately determine the fundamental properties of these systems.

Research of Precataclysmic Variables with Radius Excesses

Science.gov (United States)

Deminova, N. R.; Shimansky, V. V.; Borisov, N. V.; Gabdeev, M. M.; Shimanskaya, N. N.

2017-06-01

The results of spectroscopic observations of the pre-cataclysmic variable NSVS 14256825, which is a HW Vir binary system, were analyzed. The chemical composition is determined, the radial velocities and equivalent widths of a given star are measured. The fundamental parameters of the components were determined (R1 = 0.166 R⊙ , M2 = 0.100 M⊙ , R2 = 0.122 R⊙). It is shown that the secondary component has a mass close to the mass of brown dwarfs. A comparison of two close binary systems is made: HS 2333 + 3927 and NSVS 14256825. A radius-to-mass relationship for the secondary components of the studied pre-cataclysmic variables is constructed. It is concluded that an excess of radii relative to model predictions for MS stars is observed in virtually all systems.

The Space-Time Asymmetry Research (STAR) program

Science.gov (United States)

Buchman, Sasha

Stanford University, NASA Ames, and international partners propose the Space-Time Asymme-try Research (STAR) program, a series of three Science and Technology Development Missions, which will probe the fundamental relationships between space, time and gravity. What is the nature of space-time? Is space truly isotropic? Is the speed of light truly isotropic? If not, what is its direction and location dependency? What are the answers beyond Einstein? How will gravity and the standard model ultimately be combined? The first mission, STAR-1, will measure the absolute anisotropy of the velocity of light to one part in 1017 , derive the Kennedy-Thorndike (KT) coefficient to 7x10-10 (150-fold improvement over modern ground measurements), derive the Michelson-Morley (MM) coefficient to 10-11 (confirming the ground measurements), and derive the coefficients of Lorentz violation in the Standard Model Exten-sion (SME), in the range 7x10-17 to 10-13 (an order of magnitude improvement over ground measurements). The follow-on missions will achieve a factor of 100 higher sensitivities. The core instruments are high stability optical cavities and high accuracy gas spectroscopy frequency standards using the "NICE-OHMS technique. STAR-1 is accomplished with a fully redundant instrument flown on a standard bus, spin-stabilized spacecraft with a mission lifetime of two years. Spacecraft and instrument have a total mass of less than 180 kg and consume less than 200 W of power. STAR-1 would launch in 2015 as a secondary payload in a 650 km, sun-synchronous orbit. We describe the STAR-1 mission in detail and the STAR series in general, with a focus on how each mission will build on the development and success of the previous missions, methodically enhancing both the capabilities of the STAR instrument suite and our understanding of this important field. By coupling state-of-the-art scientific instrumentation with proven and cost-effective small satellite technology in an environment

Observing Compact Stars with AstroSat

Indian Academy of Sciences (India)

Dipankar Bhattacharya

2017-09-12

Sep 12, 2017 ... based observatory for compact star research. An account is given of ... unprecedented capability to study such rapid variability simultaneously at all ..... Physical Research Laboratory, University of Leicester and the Canadian ...

Interesting star V 627 Cas (=AS 501) is a young object, a Mira variable or a binary symbiotic system

International Nuclear Information System (INIS)

Kolotilov, E.A.

1988-01-01

The results of spectral and photometric observations of the variable star V 627 Cas carried out in optical and infrared range are presented. The combination of all available data shows the following parameters of the star: spectral class corresponds on the average to M4 bearing some features of high-luminocity. In the emission spectrum the most prominent are hydrogen lines. The star shows strong UV and IR excesses, variable linear polarization in the optical range, with the star are also connected maser lines OH and H 2 O. The brightness of V 627 Cas in the photographic region has decreased for at least 50 years on the average by ∼ 0 m .04 per year

A survey for variable young stars with small telescopes: First results from HOYS-CAPS

Science.gov (United States)

Froebrich, D.; Campbell-White, J.; Scholz, A.; Eislöffel, J.; Zegmott, T.; Billington, S. J.; Donohoe, J.; Makin, S. V.; Hibbert, R.; Newport, R. J.; Pickard, R.; Quinn, N.; Rodda, T.; Piehler, G.; Shelley, M.; Parkinson, S.; Wiersema, K.; Walton, I.

2018-05-01

Variability in Young Stellar Objects (YSOs) is one of their primary characteristics. Long-term, multi-filter, high-cadence monitoring of large YSO samples is the key to understand the partly unusual light-curves that many of these objects show. Here we introduce and present the first results of the HOYS-CAPScitizen science project which aims to perform such monitoring for nearby (d < 1 kpc) and young (age < 10 Myr) clusters and star forming regions, visible from the northern hemisphere, with small telescopes. We have identified and characterised 466 variable (413 confirmed young) stars in 8 young, nearby clusters. All sources vary by at least 0.2 mag in V, have been observed at least 15 times in V, R and I in the same night over a period of about 2 yrs and have a Stetson index of larger than 1. This is one of the largest samples of variable YSOs observed over such a time-span and cadence in multiple filters. About two thirds of our sample are classical T-Tauri stars, while the rest are objects with depleted or transition disks. Objects characterised as bursters show by far the highest variability. Dippers and objects whose variability is dominated by occultations from normal interstellar dust or dust with larger grains (or opaque material) have smaller amplitudes. We have established a hierarchical clustering algorithm based on the light-curve properties which allows the identification of the YSOs with the most unusual behaviour, and to group sources with similar properties. We discuss in detail the light-curves of the unusual objects V2492 Cyg, V350 Cep and 2MASS J21383981+5708470.

Uncertain Classification of Variable Stars: Handling Observational GAPS and Noise

Science.gov (United States)

Castro, Nicolás; Protopapas, Pavlos; Pichara, Karim

2018-01-01

Automatic classification methods applied to sky surveys have revolutionized the astronomical target selection process. Most surveys generate a vast amount of time series, or “lightcurves,” that represent the brightness variability of stellar objects in time. Unfortunately, lightcurves’ observations take several years to be completed, producing truncated time series that generally remain without the application of automatic classifiers until they are finished. This happens because state-of-the-art methods rely on a variety of statistical descriptors or features that present an increasing degree of dispersion when the number of observations decreases, which reduces their precision. In this paper, we propose a novel method that increases the performance of automatic classifiers of variable stars by incorporating the deviations that scarcity of observations produces. Our method uses Gaussian process regression to form a probabilistic model of each lightcurve’s observations. Then, based on this model, bootstrapped samples of the time series features are generated. Finally, a bagging approach is used to improve the overall performance of the classification. We perform tests on the MAssive Compact Halo Object (MACHO) and Optical Gravitational Lensing Experiment (OGLE) catalogs, results show that our method effectively classifies some variability classes using a small fraction of the original observations. For example, we found that RR Lyrae stars can be classified with ~80% accuracy just by observing the first 5% of the whole lightcurves’ observations in the MACHO and OGLE catalogs. We believe these results prove that, when studying lightcurves, it is important to consider the features’ error and how the measurement process impacts it.

New variable stars discovered in the fields of three Galactic open clusters using the VVV survey

Science.gov (United States)

Palma, T.; Minniti, D.; Dékány, I.; Clariá, J. J.; Alonso-García, J.; Gramajo, L. V.; Ramírez Alegría, S.; Bonatto, C.

2016-11-01

This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the J-, H- and Ks- bands obtained from the Vista Variables in the Vía Láctea (VVV) Survey. We performed in each cluster field a variability search using Stetson's variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study, 157 in total in three different known OCs, are classified based on their light curve shapes, periods, amplitudes and their location in the corresponding color-magnitude (J -Ks ,Ks) and color-color (H -Ks , J - H) diagrams. We found 5 possible Cepheid stars which, based on the period-luminosity relation, are very likely type II Cepheids located behind the bulge. Among the newly discovered variables, there are eclipsing binaries, δ Scuti, as well as background RR Lyrae stars. Using the new version of the Wilson & Devinney code as well as the "Physics Of Eclipsing Binaries" (PHOEBE) code, we analyzed some of the best eclipsing binaries we discovered. Our results show that these studied systems turn out to be ranging from detached to double-contact binaries, with low eccentricities and high inclinations of approximately 80°. Their surface temperatures range between 3500 K and 8000 K.

A recurrent neural network for classification of unevenly sampled variable stars

Science.gov (United States)

Naul, Brett; Bloom, Joshua S.; Pérez, Fernando; van der Walt, Stéfan

2018-02-01

Astronomical surveys of celestial sources produce streams of noisy time series measuring flux versus time (`light curves'). Unlike in many other physical domains, however, large (and source-specific) temporal gaps in data arise naturally due to intranight cadence choices as well as diurnal and seasonal constraints1-5. With nightly observations of millions of variable stars and transients from upcoming surveys4,6, efficient and accurate discovery and classification techniques on noisy, irregularly sampled data must be employed with minimal human-in-the-loop involvement. Machine learning for inference tasks on such data traditionally requires the laborious hand-coding of domain-specific numerical summaries of raw data (`features')7. Here, we present a novel unsupervised autoencoding recurrent neural network8 that makes explicit use of sampling times and known heteroskedastic noise properties. When trained on optical variable star catalogues, this network produces supervised classification models that rival other best-in-class approaches. We find that autoencoded features learned in one time-domain survey perform nearly as well when applied to another survey. These networks can continue to learn from new unlabelled observations and may be used in other unsupervised tasks, such as forecasting and anomaly detection.

LONG-TERM LIGHT CURVE OF HIGHLY VARIABLE PROTOSTELLAR STAR GM CEP

International Nuclear Information System (INIS)

Xiao Limin; Kroll, Peter; Henden, Arne A.

2010-01-01

We present data from the archival plates at Harvard College Observatory and Sonneberg Observatory showing the field of the solar-type pre-main-sequence star GM Cep. A total of 186 magnitudes of GM Cep have been measured on these archival plates, with 176 in blue sensitivity, six in visible, and four in red. We combine our data with data from the literature and from the American Association of Variable Star Observers to depict the long-term light curves of GM Cep in both B and V wavelengths. The light curves span from 1895 until now, with two densely sampled regions (1935-1945 in the B band, and 2006 until now in the V band). The long-term light curves do not show any fast rise behavior as predicted by an accretion mechanism. Both the light curves and the magnitude histograms confirm the conclusion that the light curves are dominated by dips (possibly from extinction) superposed on some quiescence state, instead of outbursts caused by accretion flares. Our result excludes the possibility of GM Cep being a FUor, EXor, or McNeil's Nebula-type star. Several special cases of T Tauri stars were checked, but none of these light curves were compatible with that of GM Cep. The lack of periodicity in the light curve excludes the possibility of GM Cep being a KH 15D system.

The nature of the nebula associated with the luminous blue variable star WRA 751

OpenAIRE

Hutsemekers, Damien; van Drom, E.

1991-01-01

Narrow-band filter imagery as well as medium to high resolution spectroscopy of the nebula surrounding the luminous blue variable (LBV) star WRA 751 are presented. The nebula appears as a slowly expanding H II region of low excitation characterized by a significant N/O overabundance which may be due to the presence in the nebula of nuclear processed material ejected by the star. With the recent discovery of a nebula around HR Car, all but one known galactic LBVs are now shown to be associated...

Double Star Research: A Student-Centered Community of Practice

Science.gov (United States)

Johnson, Jolyon

2016-06-01

Project and team-based pedagogies are increasingly augmenting lecture-style science classrooms. Occasionally, university professors will invite students to tangentially partcipate in their research. Since 2006, Dr. Russ Genet has led an astronomy research seminar for community college and high school students that allows participants to work closely with a melange of professional and advanced amatuer researchers. The vast majority of topics have centered on measuring the position angles and searations of double stars which can be readily published in the Journal of Double Star Observations. In the intervening years, a collaborative community of practice (Wenger, 1998) formed with the students as lead researchers on their projects with the guidance of experienced astronomers and educators. The students who join the research seminar are often well prepared for further STEM education in college and career. Today, the research seminar involves multile schools in multiple states with a volunteer educator acting as an assistant instructor at each location. These assistant instructors interface with remote observatories, ensure progress is made, and recruit students. The key deliverables from each student team include a published research paper and a public presentation online or in-person. Citing a published paper on scholarship and college applications gives students' educational carreers a boost. Recently the Journal of Double Star Observations published its first special issue of exlusively student-centered research.

Four new Delta Scuti stars

Science.gov (United States)

Schutt, R. L.

1991-01-01

Four new Delta Scuti stars are reported. Power, modified into amplitude, spectra, and light curves are used to determine periodicities. A complete frequency analysis is not performed due to the lack of a sufficient time base in the data. These new variables help verify the many predictions that Delta Scuti stars probably exist in prolific numbers as small amplitude variables. Two of these stars, HR 4344 and HD 107513, are possibly Am stars. If so, they are among the minority of variable stars which are also Am stars.

The primary role of the SW Sextantis stars in the evolution of cataclysmic variables

Science.gov (United States)

Torres, Manuel; Gaensicke, Boris; Rodriguez-Gil, Pablo; Long, Knox; Marsh, Tom; Steeghs, Danny; Munoz-Darias, Teodoro; Shahbaz, Tariq; Schmidtobreick, Linda; Schreiber, Matthias

2009-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) which plays a fundamental role in our understanding of CV structure and evolution. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the binary parameters, white dwarf temperature, and distance to the system for a SW Sex star for the first time. The measured stellar masses and radii will especially be a precious input to the theory of compact binary evolution as a whole.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

Science.gov (United States)

Torres, Manuel; Steeghs, Danny; Gaensicke, Boris; Marsh, Tom; Rodriguez-Gil, Pablo; Schmidtobreick, Linda; Long, Knox; Schreiber, Matthias

2007-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

Stellar parameters and H α line profile variability of Be stars in the BeSOS survey

Science.gov (United States)

Arcos, C.; Kanaan, S.; Chávez, J.; Vanzi, L.; Araya, I.; Curé, M.

2018-03-01

The Be phenomenon is present in about 20 per cent of B-type stars. Be stars show variability on a broad range of time-scales, which in most cases is related to the presence of a circumstellar disc of variable size and structure. For this reason, a time-resolved survey is highly desirable in order to understand the mechanisms of disc formation, which are still poorly understood. In addition, a complete observational sample would improve the statistical significance of the study of stellar and disc parameters. The `Be Stars Observation Survey' (BeSOS) is a survey containing reduced spectra obtained using the Pontifica Universidad Católica High Echelle Resolution Optical Spectrograph (PUCHEROS) with a spectral resolution of 17 000 in the range 4260-7300 Å. BeSOS's main objective is to offer consistent spectroscopic and time-resolved data obtained with one instrument. The user can download or plot the data and obtain stellar parameters directly from the website. We also provide a star-by-star analysis based on photometric, spectroscopic and interferometric data, as well as general information about the whole BeSOS sample. Recently, BeSOS led to the discovery of a new Be star HD 42167 and facilitated study of the V/R variation of HD 35165 and HD 120324, the steady disc of HD 110335 and the Be shell status of HD 127972. Optical spectra used in this work, as well as the stellar parameters derived, are available online at http://besos.ifa.uv.cl.

MSU Contributes to New Research on Star Formation

Science.gov (United States)

2010-01-01

EAST LANSING, Mich. - "Crazy" and "cool" are two of the words Michigan State University astronomer Megan Donahue uses to describe the two distinct "tails" found on a long tail of gas that is believed to be forming stars where few stars have been formed before. Donahue was part of an international team of astronomers that viewed the gas tail with a very long, new observation made by the Chandra X-ray Observatory and detailed it in a paper published this month in the publication Astrophysical Journal. "The double tail is very cool - that is, interesting - and ridiculously hard to explain," said Donahue, a professor in MSU's Department of Physics and Astronomy. "It could be two different sources of gas or something to do with magnetic fields. We just don't know." What is also unusual is the gas tail, which is more than 200,000 light years in length, extends well outside any galaxy. It is within objects such as this that new stars are formed, but usually within the confines of a galaxy. "This system is really crazy because where we're seeing the star formation is well away from any galaxy," Donahue said. "Star formation happens primarily in the disks of galaxies. What we're seeing here is very unexpected." This gas tail was originally spotted by astronomers three years ago using a multitude of telescopes, including NASA's Chandra X-ray Observatory and the SOuthern Astrophysical Research telescope, a Chilean-based observatory in which MSU is one of the partners. The new observations show a second tail, and a fellow galaxy, ESO 137-002, that also has a tail of hot X-ray-emitting gas. How these newly formed stars came to be in this particular place remains a mystery as well. Astronomers theorize this gas tail might have "pulled" star-making material from nearby gases, creating what some have called "orphan stars." "This system continues to surprise us as we get better observations of it," Donahue said. The gas tail is located in the southern hemisphere near a

Spectroscopic Variability of Supergiant Star HD14134, B3Ia

Indian Academy of Sciences (India)

Y. M. Maharramov

2017-06-19

Jun 19, 2017 ... the hot supergiant HD14134 studied in the present paper has a mass-loss rate of ...... tific program for the priority fields of research of the. National .... emission-line stars in the Large Magellanic Cloud, Astron. Astrophys., 158 ...

Nonradial pulsations of hot evolved stars

International Nuclear Information System (INIS)

Starrfield, S.G.

1987-01-01

There are three classes of faint blue variable stars: the ZZ Ceti variables (DAV degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (DOV degenerate dwarfs). None of these classes of variable stars were known at the time of the last blue star meeting. Observational and theoretical studies of the ZZ Ceti variables, the DBV variables, and the GW Vir variables have shown them to be pulsating in nonradial g-modes. The cause of the pulsation has been determined for each class of variable star and, in all cases, also involves predictions of the stars envelope composition. The predictions are that the ZZ Ceti variables must have pure hydrogen surface layers, the DBV stars must have pure helium surface layers, and the GW Vir stars must have carbon and oxygen rich surface layers with less than 30% (by mass) of helium. Given these compositions, it is found that pulsation driving occurs as a result of the kappa and gamma effects operating in the partial ionization zones of either hydrogen or helium. In addition, a new driving mechanism, called convection blocking, also occurs in these variables. For the GW Vir variables, it is the kappa and gamma effects in the partial ionization regions of carbon and oxygen. 45 refs

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

Energy Technology Data Exchange (ETDEWEB)

Humphreys, Roberta M.; Davidson, Kris; Hahn, David [Minnesota Institute for Astrophysics, 116 Church St SE, University of Minnesota, Minneapolis, MN 55455 (United States); Martin, John C. [Barber Observatory, University of Illinois, Springfield, IL 62703 (United States); Weis, Kerstin, E-mail: roberta@umn.edu [Astronomical Institute, Ruhr-Universitaet Bochum (Germany)

2017-07-20

We present HR diagrams for the massive star populations in M31 and M33, including several different types of emission-line stars: the confirmed luminous blue variables (LBVs), candidate LBVs, B[e] supergiants, and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip that supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with the infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs (red supergiants) like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.

X-Ray Intraday Variability of Five TeV Blazars with NuSTAR

Energy Technology Data Exchange (ETDEWEB)

Pandey, Ashwani; Gupta, Alok C. [Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263002 (India); Wiita, Paul J., E-mail: ashwanitapan@gmail.com, E-mail: acgupta30@gmail.com, E-mail: wiitap@tcnj.edu [Department of Physics, The College of New Jersey, 2000 Pennington Road, Ewing, NJ 08628-0718 (United States)

2017-06-01

We have examined 40 Nuclear Spectroscopic Telescope Array ( NuSTAR ) light curves (LCs) of five TeV emitting high synchrotron peaked blazars: 1ES 0229+200, Mrk 421, Mrk 501, 1ES 1959+650, and PKS 2155−304. Four of the blazars showed intraday variability in the NuSTAR energy range of 3–79 keV. Using an autocorrelation function analysis we searched for intraday variability timescales in these LCs and found indications of several between 2.5 and 32.8 ks in eight LCs of Mrk 421, a timescale around 8.0 ks for one LC of Mrk 501, and timescales of 29.6 and 57.4 ks in two LCs of PKS 2155-304. The other two blazars’ LCs do not show any evidence for intraday variability timescales shorter than the lengths of those observations; however, the data were both sparser and noisier for them. We found positive correlations with zero lag between soft (3–10 keV) and hard (10–79 keV) bands for most of the LCs, indicating that their emissions originate from the same electron population. We examined spectral variability using a hardness ratio analysis and noticed a general “harder-when-brighter” behavior. The 22 LCs of Mrk 421 observed between 2012 July and 2013 April show that this source was in a quiescent state for an extended period of time and then underwent an unprecedented double-peaked outburst while monitored on a daily basis during 2013 April 10–16. We briefly discuss models capable of explaining these blazar emissions.

On Gammelgaard's Formula for a Star Product with Separation of Variables

Science.gov (United States)

Karabegov, Alexander

2013-08-01

We show that Gammelgaard's formula expressing a star product with separation of variables on a pseudo-Kähler manifold in terms of directed graphs without cycles is equivalent to an inversion formula for an operator on a formal Fock space. We prove this inversion formula directly and thus offer an alternative approach to Gammelgaard's formula which gives more insight into the question why the directed graphs in his formula have no cycles.

Near-infrared variability study of the central 2.3 × 2.3 arcmin2 of the Galactic Centre - II. Identification of RR Lyrae stars in the Milky Way nuclear star cluster

Science.gov (United States)

Dong, Hui; Schödel, Rainer; Williams, Benjamin F.; Nogueras-Lara, Francisco; Gallego-Cano, Eulalia; Gallego-Calvente, Teresa; Wang, Q. Daniel; Rich, R. Michael; Morris, Mark R.; Do, Tuan; Ghez, Andrea

2017-11-01

Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K ≥ 15) stellar population in the Milky Way's nuclear star cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analysed HST/WFC3/IR observations of the central 2.3 × 2.3 arcmin2 of the Milky Way and found 21 variable stars with periods between 0.2 and 1 d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as 4 RRc stars, 4 RRab stars, 3 RRab candidates and 10 binaries. Especially, the four RRab stars show sawtooth light curves and fall exactly on to the Oosterhoff I division in the Bailey diagram. Compared to the RRab stars reported by Minniti et al., our new RRab stars have higher extinction (AK > 1.8) and should be closer to the Galactic Centre. The extinction and distance of one RRab stars match those for the Milky Way's nuclear star cluster given in previous works. We perform simulations and find that after correcting for incompleteness, there could be not more than 40 RRab stars within the Milky Way's nuclear star cluster and in our field of view. Through comparing with the known globular clusters of the Milky Way, we estimate that if there exists an old, metal-poor (-1.5 < [Fe/H] < -1) stellar population in the Milky Way nuclear star cluster on a scale of 5 × 5 pc, then it contributes at most 4.7 × 105 M⊙, I.e. ˜18 per cent of the stellar mass.

Kepler observations of variability in B-type stars

OpenAIRE

Balona, L. A.; Pigulski, A.; De Cat, P.; Handler, G.; Gutierrez-Soto, J; Engelbrecht, C. A.; Frescura, F.; Briquet, M.; Cuypers, J.; Daszynska-Daszkiewicz, J.; Degroote, P.; Dukes, R. J.; Garcia, R. A.; Green, E. M.; Heber, U.

2011-01-01

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies characteristic of SPB stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB/beta Cep hybrids. In all cases the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree ...

DISCOVERY OF MIRA VARIABLE STARS IN THE METAL-POOR SEXTANS DWARF SPHEROIDAL GALAXY

Energy Technology Data Exchange (ETDEWEB)

Sakamoto, Tsuyoshi [Japan Spaceguard Association, 1716-3 Ookura, Bisei, Ibara, Okayama 714-1411 (Japan); Matsunaga, Noriyuki; Nakada, Yoshikazu [Kiso Observatory, Institute of Astronomy, School of Science, University of Tokyo, 10762-30 Mitake, Kiso-machi, Kiso-gun, Nagano 397-0101 (Japan); Hasegawa, Takashi, E-mail: sakamoto@spaceguard.or.jp [Gunma Astronomical Observatory, 6860-86 Nakayama, Takayama, Agatsuma, Gunma 377-0702 (Japan)

2012-12-10

We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal galaxy (dSph). We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the I{sub c} band show large-amplitude (3.7 and 0.9 mag) and long-period (326 {+-} 15 and 122 {+-} 5 days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras (75.3{sup +12.8}{sub -10.9} and 79.8{sup +11.5}{sub -9.9} kpc, respectively), together with the radial velocities available, support memberships of the Sextans dSph (90.0 {+-} 10.0 kpc). These are the first Miras found in a stellar system with a metallicity as low as [Fe/H] {approx} -1.9 than any other known system with Miras.

Preliminary results of variable star search using KMTNet data

Directory of Open Access Journals (Sweden)

Jeon Young-Beom

2017-01-01

Full Text Available The KMTNet (Korea Microlensing Telescope Network was completed on October 2nd in 2015. There are three 1.6 m telescopes in Chile (CTIO, Australia (SSO and South Africa (SAAO. The field of view of the CCD camera is 2 degree × 2 degree. We are monitoring and observing the bulge region for 24-hour continuous observations using the KMTNet telescopes. I present the characteristics of CCD camera and telescope, and the status of observation programs. We are still developing CCD cameras to accurate photometry. From the KMTNet data, we can obtain accurate 24-hour continuous time-series data for many variable stars.

YSOVAR: MID-INFRARED VARIABILITY AMONG YSOs IN THE STAR FORMATION REGION GGD12-15

Energy Technology Data Exchange (ETDEWEB)

Wolk, Scott J.; Günther, H. Moritz; Poppenhaeger, Katja; Forbrich, J. [Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Cody, A. M. [NASA Ames Research Center, M/S 244-5 Moffett Field, CA 94035 (United States); Rebull, L. M.; Stauffer, J. R. [Spitzer Science Center/Caltech, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Hillenbrand, L. A. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Plavchan, P. [Department of Physics Astronomy and Materials Science, Missouri State University, Springfield, MO 65897 (United States); Covey, K. R. [Department of Physics and Astronomy, Western Washington Univ., Bellingham, WA 98225-9164 (United States); Song, Inseok, E-mail: swolk@cfa.harvard.edu [Physics and Astronomy Department, University of Georgia, Athens, GA 30602-2451 (United States)

2015-11-15

We present an IR-monitoring survey with the Spitzer Space Telescope of the star-forming region GGD 12-15. More than 1000 objects were monitored, including about 350 objects within the central 5′, which is found to be especially dense in cluster members. The monitoring took place over 38 days and is part of the Young Stellar Object VARiability project. The region was also the subject of a contemporaneous 67 ks Chandra observation. The field includes 119 previously identified pre-main sequence star candidates. X-rays are detected from 164 objects, 90 of which are identified with cluster members. Overall, we find that about half the objects in the central 5′ are young stellar objects (YSOs) based on a combination of their spectral energy distribution, IR variability, and X-ray emission. Most of the stars with IR excess relative to a photosphere show large amplitude (>0.1 mag) mid-infrared (mid-IR) variability. There are 39 periodic sources, and all but one is found to be a cluster member. Almost half of the periodic sources do not show IR excesses. Overall, more than 85% of the Class I, flat spectrum, and Class II sources are found to vary. The amplitude of the variability is larger in more embedded YSOs. Most of the Class I/II objects exhibit redder colors in a fainter state, which is compatible with time-variable extinction. A few become bluer when fainter, which can be explained with significant changes in the structure of the inner disk. A search for changes in the IR due to X-ray events is carried out, but the low number of flares prevented an analysis of the direct impact of X-ray flares on the IR light curves. However, we find that X-ray detected Class II sources have longer timescales for change in the MIR than a similar set of non-X-ray detected Class IIs.

Photometry of Variable Stars, and System Transformability Over Long Time Intervals

Directory of Open Access Journals (Sweden)

Sterken C.

2003-12-01

Full Text Available The fundamental problem of long-term photometric monitoring of variable stars and of multi-wavelength photometric campaigns is the problem of bringing the data to a common standard. Such homogenization can be achieved only when the measurements are made in photometric systems that are truly transformable. This fundamental problem is of a technical nature, and photometric observers, sometimes, are not aware of the problems. This frequently leads to over-interpretation of the data.

Prototype pipeline to search for variable stars in the Ondfejov D50 archive

Czech Academy of Sciences Publication Activity Database

Novotný, F.; Jelínek, Martin

2017-01-01

Roč. 47, č. 2 (2017), s. 133-136 ISSN 1335-1842. [INTEGRAL/BART Workshop /14./. Karlovy Vary, 03.04.2017-07.04.2017] Institutional support: RVO:67985815 Keywords : variable stars * photometry * D50 telescope Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 0.336, year: 2016

The variable Herbig Ae star HR 5999: VIII. Spectroscopic observations 1975 - 1985 and correlations with simulataneous photometry

International Nuclear Information System (INIS)

Tjin, A.; Djie, H.R.E.; The, P.S.; Andersen, J.; Nordstroem, B.; Finkenzeller, U.; Jankovics, I.

1989-01-01

Visual spectroscopy of the irregularly variable Herbig Ae star HR 5999 over the past 15 years is summarised. The general features of the spectrum indicate that HR 5999 is an A5-7 III-IVe star with an extended circumstellar atmosphere. Typical lines have a rotationally broadened photospheric component and one or two blue-shifted ''shell'' components. The average radial velocity of the photospheric components, together with the common proper motions of the stars strongly suggest that HR 5999 and the peculiar B6 star HR 6000 from a physical pair, with common age. In order to study the relation between variations in the spectrum and in the brightness of the star, three sequences of simultaneous spectroscopic and photometric observations have been obtained during the past decade. From these and other (isolated) simultaneous observations we concluded that: (a) the photospheric radial velocity component is variable, possibly with a period of about 14 days, which could point to the presence of a close companion, (b) occasionally, sudden variations may occur (within one night) either in the photospheric line components,or in the shell (absorption or emission) components or both; (c) a decreasing brightness is correlated with increasing Hα-emission flux and a decreasing wind velocity in the shell region. An interpretation of these correlations in terms of magnetic activity is proposed

A precursive study of the time-domain survey of the Galactic Anti-center using the Nanshan 1-meter telescope with variable stars detected

Science.gov (United States)

Ma, Shu-Guo; Esamdin, Ali; Ma, Lu; Niu, Hu-Biao; Fu, Jian-Ning; Zhang, Yu; Liu, Jin-Zhong; Yang, Tao-Zhi; Song, Fang-Fang; Pu, Guang-Xin

2018-04-01

Following the LAMOST Spectroscopic Survey and the Xuyi's Photometric Survey of the Galactic Anti-center, we plan to carry out a time-domain survey of the Galactic Anti-center (TDS-GAC) to study variable stars by using the Nanshan 1-meter telescope. Before the beginning of TDS-GAC, a precursive sky survey (PSS) has been executed. The goal of the PSS is to optimize the observation strategy of TDS-GAC and to detect some strong transient events, as well as to find some short time-scale variable stars of different types. By observing a discontinuous sky area of 15.03 deg2 with the standard Johnson-Cousin-Bessel V filter, 48 variable stars are found and the time series are analyzed. Based on the behaviors of the light curves, 28 eclipsing binary stars, 10 RR Lyraes, 3 periodic pulsating variables of other types have been classified. The rest 7 variables stay unclassified with deficient data. In addition, the observation strategy of TD-GAC is described, and the pipeline of data reduction is tested.

Cataclysmic Variables and Active Binary Stars in Omega Centauri

Science.gov (United States)

Arias, T.; Brochmann, M.; Dorfman, J. L.; White, M. V.; Cool, A. M.

2004-12-01

We report findings from our ongoing research on the globular cluster Omega Centauri (NGC 5139) using a 3x3 mosaic of Wide Field Camera pointings with the HST Advanced Camera for Surveys (ACS). The data consist of F435W (B435), F625W (R625), and F658N (Hα ) images and cover roughly 10x10 arcminutes, out to beyond the cluster's half-mass radius. Our current work is a search for cataclysmic variables (CVs) and active binaries (ABs) (e.g., RS CVn and BY Dra stars) as counterparts to X-ray point sources previously detected with Chandra. The ACS field encompasses 109 of the Chandra sources, 20-50 of which are likely to be cluster members according to our statistical estimates (the rest being primarily active galaxies). Using DAOPHOT to obtain photometry in 20x20 arcsecond patches surrounding each X-ray source, we are constructing color-magnitude diagrams to search for stars with Hα -R625 and/or B435-R625 colors indicative of CVs or ABs in ˜ 1 arcsecond Chandra error circles. With roughly half of the patches analyzed, several AB candidates and only a small number of CV candidates have emerged. Our tentative conclusion is that CVs may be significantly rarer in Omega Cen than in 47 Tuc, in contrast to the comparable numbers ( ˜100) predicted for these two clusters from tidal capture theory (Di Stefano and Rappaport 1994). Alternatively, the CVs could be strongly concentrated toward the cluster center, and thus not yet appear in our sample. To date, most of the patches we have analyzed are 3-4 arcminutes from the cluster center and thus are outside the cluster core (radius 2.6 arcminutes). Our continuing work should soon enable us to resolve this question. This work is supported by NASA grant GO-9442 from the Space Telescope Science Institute.

Kepler observations of the variability in B-type stars

DEFF Research Database (Denmark)

Balona, Luis A.; Pigulski, A.; De Cat, P.

2011-01-01

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could be cons...

STRUCTURAL VARIABLE ON THE JOB SATISFACTION OF 4 AND 5 STARRED HOTEL EMPLOYEES IN SURABAYA

Directory of Open Access Journals (Sweden)

Agustinus Nugroho

2014-01-01

Full Text Available   The study aimed to find out the effect of management’s controllable factor, which was called internal factor or structural variable, on the job satisfaction of the 4 and 5 starred hotel employees’ in Surabaya. The study used quantitative explanative technique to explain the effect of structural variable on employees’ job sa-tisfaction. The result showed that structural variable had a positive and significant effect on job satisfaction. It is also found that employees’ job satisfaction was high when there was (or the highest indicator for structural variable was fellow employees’ support and supervisor’s support, while the lowest indicator was job routine; the highest indicator for job satisfaction was satisfaction in salary, while the lowest indicator was supervisor’s competency in performing his or her tasks. The study aimed to find out the effect of management’s controllable factor, which was called internal factor or structural variable, on the job satisfaction of the 4 and 5 starred hotel employees’ in Surabaya. The study used quantitative explanative technique to explain the effect of structural variable on employees’ job sa-tisfaction. The result showed that structural variable had a positive and significant effect on job satisfaction. It is also found that employees’ job satisfaction was high when there was (or the highest indicator for structural variable was fellow employees’ support and supervisor’s support, while the lowest indicator was job routine; the highest indicator for job satisfaction was satisfaction in salary, while the lowest indicator was supervisor’s competency in performing his or her tasks.

STAR - Research Experiences at National Laboratory Facilities for Pre-Service and Early Career Teachers

Science.gov (United States)

Keller, J. M.; Rebar, B.; Buxner, S.

2012-12-01

The STEM Teacher and Researcher (STAR) Program provides pre-service and beginning teachers the opportunity to develop identity as both teachers and researchers early in their careers. Founded and implemented by the Center for Excellence in Science and Mathematics Education (CESaME) at California Polytechnic State University on behalf of the California State University (CSU) system, STAR provides cutting edge research experiences and career development for students affiliated with the CSU system. Over the past three summers, STAR has also partnered with the NSF Robert Noyce Teacher Scholarship Program to include Noyce Scholars from across the country. Key experiences are one to three summers of paid research experience at federal research facilities associated with the Department of Energy (DOE), National Aeronautics and Space Administration (NASA), National Oceanic and Atmospheric Association (NOAA), and the National Optical Astronomy Observatory (NOAO). Anchoring beginning teachers in the research community enhances participant understanding of what it means to be both researchers and effective teachers. Since its inception in 2007, the STAR Program has partnered with 15 national lab facilities to provide 290 research experiences to 230 participants. Several of the 68 STAR Fellows participating in the program during Summer 2012 have submitted abstracts to the Fall AGU Meeting. Through continued partnership with the Noyce Scholar Program and contributions from outside funding sources, the CSU is committed to sustaining the STAR Program in its efforts to significantly impact teacher preparation. Evaluation results from the program continue to indicate program effectiveness in recruiting high quality science and math majors into the teaching profession and impacting their attitudes and beliefs towards the nature of science and teaching through inquiry. Additionally, surveys and interviews are being conducted of participants who are now teaching in the classroom as

Golden Era of Cataclysmic Variables and Related Objects: concluding remarks

Czech Academy of Sciences Publication Activity Database

Hudec, René

2012-01-01

Roč. 83, č. 2 (2012), s. 883-890 ISSN 0037-8720. [Workshop on the golden age of cataclysmic variables and related objects /2./. Palermo , 09.09.2013-14.09.2013] R&D Projects: GA ČR GA205/08/1207 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * variable stars * cataclysmic variables Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

The central star candidate of the planetary nebula Sh2-71: photometric and spectroscopic variability

Science.gov (United States)

Močnik, T.; Lloyd, M.; Pollacco, D.; Street, R. A.

2015-07-01

We present the analysis of several newly obtained and archived photometric and spectroscopic data sets of the intriguing and yet poorly understood 13.5 mag central star candidate of the bipolar planetary nebula Sh2-71. Photometric observations confirmed the previously determined quasi-sinusoidal light curve with a period of 68 d and also indicated periodic sharp brightness dips, possibly eclipses, with a period of 17.2 d. In addition, the comparison between U and V light curves revealed that the 68 d brightness variations are accompanied by a variable reddening effect of ΔE(U - V) = 0.38. Spectroscopic data sets demonstrated pronounced variations in spectral profiles of Balmer, helium and singly ionized metal lines and indicated that these variations occur on a time-scale of a few days. The most accurate verification to date revealed that spectral variability is not correlated with the 68 d brightness variations. The mean radial velocity of the observed star was measured to be ˜26 km s-1 with an amplitude of ±40 km s-1. The spectral type was determined to be B8V through spectral comparison with synthetic and standard spectra. The newly proposed model for the central star candidate is a Be binary with a misaligned precessing disc.

IRAS variables as galactic structure tracers - Classification of the bright variables

Science.gov (United States)

Allen, L. E.; Kleinmann, S. G.; Weinberg, M. D.

1993-01-01

The characteristics of the 'bright infrared variables' (BIRVs), a sample consisting of the 300 brightest stars in the IRAS Point Source Catalog with IRAS variability index VAR of 98 or greater, are investigated with the purpose of establishing which of IRAS variables are AGB stars (e.g., oxygen-rich Miras and carbon stars, as was assumed by Weinberg (1992)). Results of the analysis of optical, infrared, and microwave spectroscopy of these stars indicate that, out of 88 stars in the BIRV sample identified with cataloged variables, 86 can be classified as Miras. Results of a similar analysis performed for a color-selected sample of stars, using the color limits employed by Habing (1988) to select AGB stars, showed that, out of 52 percent of classified stars, 38 percent are non-AGB stars, including H II regions, planetary nebulae, supergiants, and young stellar objects, indicating that studies using color-selected samples are subject to misinterpretation.

YSOVAR: Mid-infrared variability in the star-forming region Lynds 1688

Energy Technology Data Exchange (ETDEWEB)

Günther, H. M.; Poppenhaeger, K.; Wolk, S. J.; Hora, J. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Cody, A. M. [Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Covey, K. R. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Hillenbrand, L. A. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Plavchan, P. [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Rebull, L. M.; Stauffer, J. R. [Spitzer Science Center/Caltech, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Allen, L. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Bayo, A. [Max Planck Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Meng, H. Y. A. [Infrared Processing and Analysis Center, California Institute of Technology, MC 100-22, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Morales-Calderón, M. [Centro de Astrobiología (INTA-CSIC), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Canada (Spain); Parks, J. R. [Department of Physics and Astronomy, Georgia State University, 25 Park Place South, Atlanta, GA 30303 (United States); Song, Inseok, E-mail: hguenther@cfa.harvard.edu [Physics and Astronomy Department, University of Georgia, Athens, GA 30602-2451 (United States)

2014-12-01

The emission from young stellar objects (YSOs) in the mid-infrared (mid-IR) is dominated by the inner rim of their circumstellar disks. We present IR data from the Young Stellar Object VARiability (YSOVAR) survey of ∼800 objects in the direction of the Lynds 1688 (L1688) star-forming region over four visibility windows spanning 1.6 yr using the Spitzer Space Telescope in its warm mission phase. Among all light curves, 57 sources are cluster members identified based on their spectral energy distribution and X-ray emission. Almost all cluster members show significant variability. The amplitude of the variability is larger in more embedded YSOs. Ten out of 57 cluster members have periodic variations in the light curves with periods typically between three and seven days, but even for those sources, significant variability in addition to the periodic signal can be seen. No period is stable over 1.6 yr. Nonperiodic light curves often still show a preferred timescale of variability that is longer for more embedded sources. About half of all sources exhibit redder colors in a fainter state. This is compatible with time-variable absorption toward the YSO. The other half becomes bluer when fainter. These colors can only be explained with significant changes in the structure of the inner disk. No relation between mid-IR variability and stellar effective temperature or X-ray spectrum is found.

XO-2b: A HOT JUPITER WITH A VARIABLE HOST STAR THAT POTENTIALLY AFFECTS ITS MEASURED TRANSIT DEPTH

International Nuclear Information System (INIS)

Zellem, Robert T.; Griffith, Caitlin A.; Pearson, Kyle A.; Fitzpatrick, M. Ryleigh; Teske, Johanna K.; Biddle, Lauren I.; Turner, Jake D.; Henry, Gregory W.; Williamson, Michael H.

2015-01-01

The transiting hot Jupiter XO-2b is an ideal target for multi-object photometry and spectroscopy as it has a relatively bright (V-mag = 11.25) K0V host star (XO-2N) and a large planet-to-star contrast ratio (R p /R s ≈ 0.015). It also has a nearby (31.″21) binary stellar companion (XO-2S) of nearly the same brightness (V-mag = 11.20) and spectral type (G9V), allowing for the characterization and removal of shared systematic errors (e.g., airmass brightness variations). We have therefore conducted a multiyear (2012–2015) study of XO-2b with the University of Arizona’s 61″ (1.55 m) Kuiper Telescope and Mont4k CCD in the Bessel U and Harris B photometric passbands to measure its Rayleigh scattering slope to place upper limits on the pressure-dependent radius at, e.g., 10 bar. Such measurements are needed to constrain its derived molecular abundances from primary transit observations. We have also been monitoring XO-2N since the 2013–2014 winter season with Tennessee State University’s Celestron-14 (0.36 m) automated imaging telescope to investigate stellar variability, which could affect XO-2b’s transit depth. Our observations indicate that XO-2N is variable, potentially due to cool star spots, with a peak-to-peak amplitude of 0.0049 ± 0.0007 R-mag and a period of 29.89 ± 0.16 days for the 2013–2014 observing season and a peak-to-peak amplitude of 0.0035 ± 0.0007 R-mag and 27.34 ± 0.21 day period for the 2014–2015 observing season. Because of the likely influence of XO-2N’s variability on the derivation of XO-2b’s transit depth, we cannot bin multiple nights of data to decrease our uncertainties, preventing us from constraining its gas abundances. This study demonstrates that long-term monitoring programs of exoplanet host stars are crucial for understanding host star variability

TIME VARIABILITY OF EMISSION LINES FOR FOUR ACTIVE T TAURI STARS. I. OCTOBER-DECEMBER IN 2010

Energy Technology Data Exchange (ETDEWEB)

Chou, Mei-Yin; Takami, Michihiro; Karr, Jennifer L.; Shang Hsien; Liu, Hauyu Baobab [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Manset, Nadine [Canada-France-Hawaii Telescope, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743 (United States); Beck, Tracy [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Pyo, Tae-Soo [Subaru Telescope, 650 North Aohoku Place, Hilo, HI 96720 (United States); Chen, Wen-Ping; Panwar, Neelam [Institute of Astronomy, National Central University, Taoyuan County 32001, Taiwan (China)

2013-04-15

We present optical spectrophotometric monitoring of four active T Tauri stars (DG Tau, RY Tau, XZ Tau, RW Aur A) at high spectral resolution (R {approx}> 1 Multiplication-Sign 10{sup 4}), to investigate the correlation between time variable mass ejection seen in the jet/wind structure of the driving source and time variable mass accretion probed by optical emission lines. This may allow us to constrain the understanding of the jet/wind launching mechanism, the location of the launching region, and the physical link with magnetospheric mass accretion. In 2010, observations were made at six different epochs to investigate how daily and monthly variability might affect such a study. We perform comparisons between the line profiles we observed and those in the literature over a period of decades and confirm the presence of time variability separate from the daily and monthly variability during our observations. This is so far consistent with the idea that these line profiles have a long-term variability (3-20 yr) related to episodic mass ejection suggested by the structures in the extended flow components. We also investigate the correlations between equivalent widths and between luminosities for different lines. We find that these correlations are consistent with the present paradigm of steady magnetospheric mass accretion and emission line regions that are close to the star.

TIME VARIABILITY OF EMISSION LINES FOR FOUR ACTIVE T TAURI STARS. I. OCTOBER–DECEMBER IN 2010

International Nuclear Information System (INIS)

Chou, Mei-Yin; Takami, Michihiro; Karr, Jennifer L.; Shang Hsien; Liu, Hauyu Baobab; Manset, Nadine; Beck, Tracy; Pyo, Tae-Soo; Chen, Wen-Ping; Panwar, Neelam

2013-01-01

We present optical spectrophotometric monitoring of four active T Tauri stars (DG Tau, RY Tau, XZ Tau, RW Aur A) at high spectral resolution (R ∼> 1 × 10 4 ), to investigate the correlation between time variable mass ejection seen in the jet/wind structure of the driving source and time variable mass accretion probed by optical emission lines. This may allow us to constrain the understanding of the jet/wind launching mechanism, the location of the launching region, and the physical link with magnetospheric mass accretion. In 2010, observations were made at six different epochs to investigate how daily and monthly variability might affect such a study. We perform comparisons between the line profiles we observed and those in the literature over a period of decades and confirm the presence of time variability separate from the daily and monthly variability during our observations. This is so far consistent with the idea that these line profiles have a long-term variability (3-20 yr) related to episodic mass ejection suggested by the structures in the extended flow components. We also investigate the correlations between equivalent widths and between luminosities for different lines. We find that these correlations are consistent with the present paradigm of steady magnetospheric mass accretion and emission line regions that are close to the star.

Pulsating variables

International Nuclear Information System (INIS)

1989-01-01

The study of stellar pulsations is a major route to the understanding of stellar structure and evolution. At the South African Astronomical Observatory (SAAO) the following stellar pulsation studies were undertaken: rapidly oscillating Ap stars; solar-like oscillations in stars; 8-Scuti type variability in a classical Am star; Beta Cephei variables; a pulsating white dwarf and its companion; RR Lyrae variables and galactic Cepheids. 4 figs

The nebular variables

CERN Document Server

Glasby, John S

1974-01-01

The Nebular Variables focuses on the nebular variables and their characteristics. Discussions are organized by type of nebular variable, namely, RW Aurigae stars, T Orionis stars, T Tauri stars, and peculiar nebular objects. Topics range from light variations of the stars to their spectroscopic and physical characteristics, spatial distribution, interaction with nebulosity, and evolutionary features. This volume is divided into four sections and consists of 25 chapters, the first of which provides general information on nebular variables, including their stellar associations and their classifi

NuSTAR and XMM-Newton observations of NGC 1365: Extreme absorption variability and a constant inner accretion disk

DEFF Research Database (Denmark)

Walton, D. J.; Risaliti, G.; Harrison, F. A.

2014-01-01

We present a spectral analysis of four coordinated NuSTAR+XMM-Newton observations of the Seyfert galaxy NGC 1365. These exhibit an extreme level of spectral variability, which is primarily due to variable line-of-sight absorption, revealing relatively unobscured states in this source for the first...

The All Sky Automated Survey. The Catalog of Bright Variable Stars in the I-band, South of Declination +28o

Science.gov (United States)

Sitek, M.; Pojmański, G.

2014-06-01

This paper presents the results of our extensive search for the bright variable stars in approximately 30 000 square degrees of the south sky in the I-band data collected by 9o×9o camera of the All Sky Automated Survey between 2002 and 2009. Lists of over 27 000 variable stars brighter than 9 mag at maximum light, with amplitudes ranging from 0.02 mag to 7 mag and variability time-scales from hours to years, as well as corresponding light curves are provided. Automated classification algorithm based on stellar properties (period, Fourier coefficients, 2MASS J, H, K, colors, ASAS V-band data) was used to roughly classify objects. Despite low spatial resolution of the ASAS data (≍15'') we cross-identified all objects with other available data sources. Coordinates of the most probable 2MASS counterparts are provided. 27 705 stars brighter than I=9 mag were found to be variable, of which 7842 objects were detected to be variable for the first time. Brief statistics and discussion of the presented data is provided. All the photometric data is available over the Internet at http://www.astrouw.edu.pl/ gp/asas/AsasBrightI.html

Effect of process variables on the osmotic dehydration of star-fruit slices

Directory of Open Access Journals (Sweden)

Camila Dalben Madeira Campos

2012-06-01

Full Text Available The objective of this work was to study the effect of blanching and the influence of temperature, solution concentration, and the initial fruit:solution ratio on the osmotic dehydration of star-fruit slices. For blanching, different concentrations of citric and ascorbic acids were studied. The samples immersed in 0.75% citric acid presented little variation in color in relation to the fresh star-fruit. Osmotic dehydration was carried out in an incubator with orbital shaking, controlled temperature, and constant shaking at 120 rpm. The influence of process variables was studied in trials defined by a complete 23 central composite design. In general, water loss and solids gain were positively influenced by temperature and by solution concentration. Nevertheless, lower temperatures reduced water loss throughout the osmotic dehydration process. An increase in the amount of dehydrating solution (initial fruit:solution ratio slightly influenced the evaluated responses. The process carried out at 50 ºC with a solution concentration of 50% resulted in a product with lower solids gain and greater water loss. Under these conditions, blanching minimized the effect of the osmotic treatment on star-fruit browning, and therefore the blanched fruits showed little variation in color in relation to the fresh fruit.

Astrophysics of cataclysmic variables by ESA Gaia and low dispersion spectroscopy

Czech Academy of Sciences Publication Activity Database

Hudec, René; Šimon, Vojtěch; Hudec, L.; Hudcová, Věra

2012-01-01

Roč. 83, č. 2 (2012), s. 849-853 ISSN 0037-8720. [Workshop on the golden age of cataclysmic variables and related objects /2./. Palermo, 09.09.2013-14.09.2013] R&D Projects: GA ČR GA205/08/1207 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * variable stars * cataclysmic variables Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

A spectroscopic search for variability of Be stars in the SMC

Czech Academy of Sciences Publication Activity Database

Baade, D.; Rivinius, Th.; Štefl, Stanislav; Kaufner, A.

2002-01-01

Roč. 383, č. 1 (2002), s. L31-L34 ISSN 0004-6361 R&D Projects: GA AV ČR IAA3003001 Institutional research plan: CEZ:AV0Z1003909 Keywords : Be stars * galaxies Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.781, year: 2002

The Safety and Tritium Applied Research (STAR) Facility: Status-2004

International Nuclear Information System (INIS)

Anderl, R.A.; Longhurst, G.R.; Pawelko, R.J.; Sharpe, J.P.; Schuetz, S.T.; Petti, D.A.

2005-01-01

The Safety and Tritium Applied Research (STAR) Facility, a US DOE National User Facility at the Idaho National Engineering and Environmental Laboratory (INEEL), comprises capabilities and infrastructure to support both tritium and non-tritium research activities important to the development of safe and environmentally friendly fusion energy. Research thrusts include (1) interactions of tritium and deuterium with plasma-facing-component (PFC) materials, (2) fusion safety issues [PFC material chemical reactivity and dust/debris generation, activation product mobilization, tritium behavior in fusion systems], and (3) molten salts and fusion liquids for tritium breeder and coolant applications. This paper updates the status of STAR and the capabilities for ongoing research activities, with an emphasis on the development, testing and integration of the infrastructure to support tritium research activities. Key elements of this infrastructure include a tritium storage and assay system, a tritium cleanup system to process glovebox and experiment tritiated effluent gases, and facility tritium monitoring systems

Searching for I-band variability in stars in the M/L spectral transition region

Science.gov (United States)

Ramsay, Gavin; Hakala, Pasi; Doyle, J. Gerry

2015-10-01

We report on I-band photometric observations of 21 stars with spectral types between M8 and L4 made using the Isaac Newton Telescope. The total amount of time for observations which had a cadence of test for photometric variability using the Kruskal-Wallis H-test and find that four sources (2MASS J10224821+5825453, 2MASS J07464256+2000321, 2MASS J16262034+3925190 and 2MASS J12464678+4027150) were found to be significantly variable at least on one epoch. Three of these sources are reported as photometrically variable for the first time. If we include sources which were deemed marginally variable, the number of variable sources is 6 (29 per cent). No flares were detected from any source. The percentage of sources which we found were variable is similar to previous studies. We summarize the mechanisms which have been put forward to explain the light curves of brown dwarfs.

XO-2b: A HOT JUPITER WITH A VARIABLE HOST STAR THAT POTENTIALLY AFFECTS ITS MEASURED TRANSIT DEPTH

Energy Technology Data Exchange (ETDEWEB)

Zellem, Robert T.; Griffith, Caitlin A. [Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, 1629 East University Boulevard, University of Arizona, Tucson, AZ 85721 (United States); Pearson, Kyle A.; Fitzpatrick, M. Ryleigh; Teske, Johanna K.; Biddle, Lauren I. [Department of Astronomy, Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Turner, Jake D. [Department of Planetary Sciences, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Henry, Gregory W.; Williamson, Michael H., E-mail: rzellem@lpl.arizona.edu, E-mail: griffith@lpl.arizona.edu [Center of Excellence in Information Systems, Tennessee State University, 3500 John A. Merritt Blvd., P.O. Box 9501, Nashville, TN 37209 (United States)

2015-09-01

The transiting hot Jupiter XO-2b is an ideal target for multi-object photometry and spectroscopy as it has a relatively bright (V-mag = 11.25) K0V host star (XO-2N) and a large planet-to-star contrast ratio (R{sub p}/R{sub s} ≈ 0.015). It also has a nearby (31.″21) binary stellar companion (XO-2S) of nearly the same brightness (V-mag = 11.20) and spectral type (G9V), allowing for the characterization and removal of shared systematic errors (e.g., airmass brightness variations). We have therefore conducted a multiyear (2012–2015) study of XO-2b with the University of Arizona’s 61″ (1.55 m) Kuiper Telescope and Mont4k CCD in the Bessel U and Harris B photometric passbands to measure its Rayleigh scattering slope to place upper limits on the pressure-dependent radius at, e.g., 10 bar. Such measurements are needed to constrain its derived molecular abundances from primary transit observations. We have also been monitoring XO-2N since the 2013–2014 winter season with Tennessee State University’s Celestron-14 (0.36 m) automated imaging telescope to investigate stellar variability, which could affect XO-2b’s transit depth. Our observations indicate that XO-2N is variable, potentially due to cool star spots, with a peak-to-peak amplitude of 0.0049 ± 0.0007 R-mag and a period of 29.89 ± 0.16 days for the 2013–2014 observing season and a peak-to-peak amplitude of 0.0035 ± 0.0007 R-mag and 27.34 ± 0.21 day period for the 2014–2015 observing season. Because of the likely influence of XO-2N’s variability on the derivation of XO-2b’s transit depth, we cannot bin multiple nights of data to decrease our uncertainties, preventing us from constraining its gas abundances. This study demonstrates that long-term monitoring programs of exoplanet host stars are crucial for understanding host star variability.

Luminosity Variations in Post-AGB Stars

Science.gov (United States)

Mesler, Robert; Henson, G.

2007-12-01

Although much is known about AGB stars and planetary nebulae, relatively little is known about the phase of a star's life in which it transitions between those two states. We have measured the variations in luminosity of a sample of known Post-AGB stars (as well as several candidates) relative to nearby, non-variable stars in order to compare them with theoretical models. The typical behavior of the observed variations is described and an attempt is made to discern whether any periodicity might be present. Luminosity variations were found to be on the order of a few hundredths to a few tenths of a magnitude for the stars that were surveyed, with occasional fluctuations of up to a magnitude. This agrees with current models of Post-AGB stars. Each star fell into one of three categories, which were termed groups 1, 2, and 3. Group 1 stars showed long term, non-periodic luminosity variations on the scale of weeks or longer and were most likely to display some sort of short term, coherent luminosity oscillation (each of which lasted for only a few cycles). Group 2 stars showed erratic, short-term magnitude variations occurring on scales of several days. Group 3 stars showed little or no variation in magnitude. Of the 27 Post-AGB stars that were sampled, five fell into group 1, fifteen fell into group 2, and seven fell into group 3. The luminosity variations tended to be color-independent, and occurred on timescales ranging nearly continuously from a few days to more than a year. No clear periodic behavior was found in any star in our sample. This project was funded by a partnership between the National Science Foundation (NSF AST-0552798), Research Experiences for Undergraduates (REU), and the Department of Defense (DoD) ASSURE (Awards to Stimulate and Support Undergraduate Research Experiences) programs.

Radio stars observed in the LAMOST spectral survey

Science.gov (United States)

Zhang, Li-Yun; Yue, Qiang; Lu, Hong-Peng; Han, Xian-Ming L.; Zhang, Yong; Shi, Jian-Rong; Wang, Yue-Fei; Hou, Yong-Hui; Zi-Huang, Cao

2017-09-01

Radio stars have attracted astronomers’ attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a large database for researching stellar spectroscopic properties of radio stars. In this work, we concentrate on their spectroscopic properties and infer physical properties from their spectra, such as stellar activity and variability. We mined big data from the LAMOST spectral survey Data Release 2 (DR2), published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys. We obtained 783 good stellar spectra with high signal to noise ratio for 659 stars. The criteria for selection were positional coincidence within 1.5‧‧ and LAMOST objects classified as stars. We calculated the equivalent widths (EWs) of the Ca ii H&K, Hδ, Hγ, Hβ, Hα and Ca ii IRT lines by integrating the line profiles. Using the EWs of the Hα line, we detected 147 active stellar spectra of 89 objects having emissions above the Hα continuum. There were also 36 objects with repeated spectra, 28 of which showed chromospheric activity variability. Furthermore, we found 14 radio stars emitting noticeably in the Ca ii IRT lines. The low value of the EW8542/EW8498 ratio for these 14 radio stars possibly alludes to chromospheric plage regions.

Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, B[e] Supergiants, and the Warm Hypergiants: How to Tell Them Apart

Energy Technology Data Exchange (ETDEWEB)

Humphreys, Roberta M.; Gordon, Michael S.; Hahn, David [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Martin, John C. [University of Illinois Springfield, Springfield, IL 62703 (United States); Weis, Kerstin, E-mail: roberta@umn.edu [Astronomical Institute, Ruhr-Universitaet Bochum (Germany)

2017-02-10

In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe ii emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission lines of [O i] and [Fe ii] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [O i] emission lines in their spectra. Some LBVs have [Fe ii] emission lines, but not all. Their SEDs show free–free emission in the near-infrared but no evidence for warm dust . Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe ii] and [O i] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA: RESULTS FROM THE 2010 OBSERVING SEASON

Energy Technology Data Exchange (ETDEWEB)

Wang, Lingzhi; Zhu, Zonghong [Department of Astronomy, Beijing Normal University, Beijing 100875 (China); Macri, Lucas M.; Wang, Lifan [Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Ashley, Michael C. B.; Lawrence, Jon S.; Luong-Van, Daniel; Storey, John W. V. [School of Physics, University of New South Wales, NSW 2052 (Australia); Cui, Xiangqun; Feng, Long-Long; Gong, Xuefei; Liu, Qiang; Shang, Zhaohui; Yang, Huigen; Yang, Ji; Yuan, Xiangyan; Zhou, Xu; Zhu, Zhenxi [Chinese Center for Antarctic Astronomy, Nanjing 210008 (China); Pennypacker, Carl R. [Center for Astrophysics, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); York, Donald G., E-mail: wanglingzhi@bao.ac.cn [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)

2013-12-01

We present results from a season of observations with the Chinese Small Telescope ARray, obtained over 183 days of the 2010 Antarctic winter. We carried out high-cadence time-series aperture photometry of 9125 stars with i ∼< 15.3 mag located in a 23 deg{sup 2} region centered on the south celestial pole. We identified 188 variable stars, including 67 new objects relative to our 2008 observations, thanks to broader synoptic coverage, a deeper magnitude limit, and a larger field of view. We used the photometric data set to derive site statistics from Dome A. Based on two years of observations, we find that extinction due to clouds at this site is less than 0.1 and 0.4 mag during 45% and 75% of the dark time, respectively.

Long-Term Variability of the Sun in the Context of Solar-Analog Stars

Science.gov (United States)

Egeland, Ricky

2018-06-01

The Sun is the best observed object in astrophysics, but despite this distinction the nature of its well-ordered generation of magnetic field in 11-year activity cycles remains a mystery. In this work, we place the solar cycle in a broader context by examining the long-term variability of solar analog stars within 5% of the solar effective temperature, but varied in rotation rate and metallicity. Emission in the Fraunhofer H & K line cores from singly-ionized calcium in the lower chromosphere is due to magnetic heating, and is a proven proxy for magnetic flux on the Sun. We use Ca H & K observations from the Mount Wilson Observatory HK project, the Lowell Observatory Solar Stellar Spectrograph, and other sources to construct composite activity time series of over 100 years in length for the Sun and up to 50 years for 26 nearby solar analogs. Archival Ca H & K observations of reflected sunlight from the Moon using the Mount Wilson instrument allow us to properly calibrate the solar time series to the S-index scale used in stellar studies. We find the mean solar S-index to be 5–9% lower than previously estimated, and the amplitude of activity to be small compared to active stars in our sample. A detailed look at the young solar analog HD 30495, which rotates 2.3 times faster than the Sun, reveals a large amplitude ~12-year activity cycle and an intermittent short-period variation of 1.7 years, comparable to the solar variability time scales despite its faster rotation. Finally, time series analyses of the solar analog ensemble and a quantitative analysis of results from the literature indicate that truly Sun-like cyclic variability is rare, and that the amplitude of activity over both long and short timescales is linearly proportional to the mean activity. We conclude that the physical conditions conducive to a quasi-periodic magnetic activity cycle like the Sun’s are rare in stars of approximately the solar mass, and that the proper conditions may be restricted

Instabilities in Interacting Binary Stars

Science.gov (United States)

Andronov, I. L.; Andrych, K. D.; Antoniuk, K. A.; Baklanov, A. V.; Beringer, P.; Breus, V. V.; Burwitz, V.; Chinarova, L. L.; Chochol, D.; Cook, L. M.; Cook, M.; Dubovský, P.; Godlowski, W.; Hegedüs, T.; Hoňková, K.; Hric, L.; Jeon, Y.-B.; Juryšek, J.; Kim, C.-H.; Kim, Y.; Kim, Y.-H.; Kolesnikov, S. V.; Kudashkina, L. S.; Kusakin, A. V.; Marsakova, V. I.; Mason, P. A.; Mašek, M.; Mishevskiy, N.; Nelson, R. H.; Oksanen, A.; Parimucha, S.; Park, J.-W.; Petrík, K.; Quiñones, C.; Reinsch, K.; Robertson, J. W.; Sergey, I. M.; Szpanko, M.; Tkachenko, M. G.; Tkachuk, L. G.; Traulsen, I.; Tremko, J.; Tsehmeystrenko, V. S.; Yoon, J.-N.; Zola, S.; Shakhovskoy, N. M.

2017-07-01

The types of instability in the interacting binary stars are briefly reviewed. The project “Inter-Longitude Astronomy” is a series of smaller projects on concrete stars or groups of stars. It has no special funds, and is supported from resources and grants of participating organizations, when informal working groups are created. This “ILA” project is in some kind similar and complementary to other projects like WET, CBA, UkrVO, VSOLJ, BRNO, MEDUZA, AstroStatistics, where many of us collaborate. Totally we studied 1900+ variable stars of different types, including newly discovered variables. The characteristic timescale is from seconds to decades and (extrapolating) even more. The monitoring of the first star of our sample AM Her was initiated by Prof. V.P. Tsesevich (1907-1983). Since more than 358 ADS papers were published. In this short review, we present some highlights of our photometric and photo-polarimetric monitoring and mathematical modeling of interacting binary stars of different types: classical (AM Her, QQ Vul, V808 Aur = CSS 081231:071126+440405, FL Cet), asynchronous (BY Cam, V1432 Aql), intermediate (V405 Aql, BG CMi, MU Cam, V1343 Her, FO Aqr, AO Psc, RXJ 2123, 2133, 0636, 0704) polars and magnetic dwarf novae (DO Dra) with 25 timescales corresponding to different physical mechanisms and their combinations (part “Polar”); negative and positive superhumpers in nova-like (TT Ari, MV Lyr, V603 Aql, V795 Her) and many dwarf novae stars (“Superhumper”); eclipsing “non-magnetic” cataclysmic variables(BH Lyn, DW UMa, EM Cyg; PX And); symbiotic systems (“Symbiosis”); super-soft sources (SSS, QR And); spotted (and not spotted) eclipsing variables with (and without) evidence for a current mass transfer (“Eclipser”) with a special emphasis on systems with a direct impact of the stream into the gainer star's atmosphere, which we propose to call “Impactor” (short from “Extreme Direct Impactor”), or V361 Lyr-type stars. Other

Technetium in late-type stars. I. Observations

International Nuclear Information System (INIS)

Little-Marenin, I.R.; Little, S.J.

1979-01-01

An analysis of about 90 spectra (11 or 13A/mm) of nonvariable and variable (mostly Mira variables) M, MS, S, CS, and C stars for the presence of the radioactive element technetium (T/sub 1/2/approx. =2 x 10 5 y) suggests that Tc is most often present at certain variability periods. Stars with no Tc I lines in their spectra can be found at most periods (P-bar=234/sup d/), whereas stars with Tc I lines have periods in most cases in excess of 300 days (P-bar=330/sup d/ +- 83/sup d/). Interpreting our data in terms of kinematic studies by Feast (1963) suggests that the stars with Tc are Pop I and that variables without Tc are largely Pop II type stars

A SPITZER IRS STUDY OF INFRARED VARIABILITY IN TRANSITIONAL AND PRE-TRANSITIONAL DISKS AROUND T TAURI STARS

International Nuclear Information System (INIS)

Espaillat, C.; Furlan, E.; D'Alessio, P.; Sargent, B.; Muzerolle, J.; Nagel, E.; Calvet, N.; Watson, Dan M.

2011-01-01

We present a Spitzer IRS study of variability in 14 T Tauri stars in the Taurus and Chamaeleon star-forming regions. The sample is composed of transitional and pre-transitional objects which contain holes and gaps in their disks. We detect variability between 5 and 38 μm in all but two of our objects on timescales of 2-3 years. Most of the variability observed can be classified as seesaw behavior, whereby the emission at shorter wavelengths varies inversely with the emission at longer wavelengths. For many of the objects we can reasonably reproduce the observed variability using irradiated disk models, particularly by changing the height of the inner disk wall by ∼20%. When the inner wall is taller, the emission at the shorter wavelengths is higher since the inner wall dominates the emission at 2-8 μm. The taller inner wall casts a larger shadow on the outer disk wall, leading to less emission at wavelengths beyond 20 μm where the outer wall dominates. We discuss how the possible presence of planets in these disks could lead to warps that cause changes in the height of the inner wall. We also find that crystalline silicates are common in the outer disks of our objects and that in the four disks in the sample with the most crystalline silicates, variability on timescales of 1 week is present. In addition to explaining the infrared variability described above, planets can create shocks and collisions which can crystallize the dust and lead to short timescale variability.

Longitudinal Research with Latent Variables

CERN Document Server

van Montfort, Kees; Satorra, Albert

2010-01-01

This book combines longitudinal research and latent variable research, i.e. it explains how longitudinal studies with objectives formulated in terms of latent variables should be carried out, with an emphasis on detailing how the methods are applied. Because longitudinal research with latent variables currently utilizes different approaches with different histories, different types of research questions, and different computer programs to perform the analysis, the book is divided into nine chapters. Starting from some background information about the specific approach, short history and the ma

X-ray stars observed in LAMOST spectral survey

Science.gov (United States)

Lu, Hong-peng; Zhang, Li-yun; Han, Xianming L.; Shi, Jianrong

2018-05-01

X-ray stars have been studied since the beginning of X-ray astronomy. Investigating and studying the chromospheric activity from X-ray stellar optical spectra is highly significant in providing insights into stellar magnetic activity. The big data of LAMOST survey provides an opportunity for researching stellar optical spectroscopic properties of X-ray stars. We inferred the physical properties of X-ray stellar sources from the analysis of LAMOST spectra. First, we cross-matched the X-ray stellar catalogue (12254 X-ray stars) from ARXA with LAMOST data release 3 (DR3), and obtained 984 good spectra from 713 X-ray sources. We then visually inspected and assigned spectral type to each spectrum and calculated the equivalent width (EW) of Hα line using the Hammer spectral typing facility. Based on the EW of Hα line, we found 203 spectra of 145 X-ray sources with Hα emission above the continuum. For these spectra we also measured the EWs of Hβ, Hγ, Hδ and Ca ii IRT lines of these spectra. After removing novae, planetary nebulae and OB-type stars, we found there are 127 X-ray late-type stars with Hα line emission. By using our spectra and results from the literature, we found 53 X-ray stars showing Hα variability; these objects are Classical T Tauri stars (CTTs), cataclysmic variables (CVs) or chromospheric activity stars. We also found 18 X-ray stars showing obvious emissions in the Ca ii IRT lines. Of the 18 X-ray stars, 16 are CTTs and 2 are CVs. Finally, we discussed the relationships between the EW of Hα line and X-ray flux.

The Berlin Exoplanet Search Telescope Ii Catalog Of Variable Stars. Ii. Characterization Of The Corot Src02 Field

Czech Academy of Sciences Publication Activity Database

Klagyivik, P.; Csizmadia, S.; Pasternacki, T.; Cabrera, J.; Chini, R.; Eigmueller, P.; Erikson, A.; Fruth, T.; Kabáth, Petr; Lemke, R.; Murphy, M.; Rauer, H.; Titz-Weider, R.

2016-01-01

Roč. 151, May (2016), 110/1-110/9 ISSN 0004-6256 Institutional support: RVO:67985815 Keywords : eclipsing binaries * variables stars * photometric techniques Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 2.609, year: 2016

Monitoring the High-Energy Radiation Environment of Exoplanets Around Low-mass Stars with SPARCS (Star-Planet Activity Research CubeSat)

Science.gov (United States)

Shkolnik, Evgenya L.; Ardila, David; Barman, Travis; Beasley, Matthew; Bowman, Judd D.; Gorjian, Varoujan; Jacobs, Daniel; Jewell, April; Llama, Joe; Meadows, Victoria; Nikzad, Shouleh; Scowen, Paul; Swain, Mark; Zellem, Robert

2018-01-01

Roughly seventy-five billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1–0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. For each target, SPARCS will observe continuously over at least one complete stellar rotation (5 - 45 days). SPARCS will also advance UV detector technology by flying high quantum efficiency, UV-optimized detectors developed at JPL. These Delta-doped detectors have a long history of deployment demonstrating greater than five times the quantum efficiency of the detectors used by GALEX. SPARCS will pave the way for their application in missions like LUVOIR or HabEx, including interim UV-capable missions. SPARCS will also be capable of ‘target-of-opportunity’ UV observations for the rocky planets in M dwarf HZs soon to be discovered by NASA’s TESS mission, providing the needed UV context for the first habitable planets that JWST will characterize.Acknowledgements: Funding for SPARCS is provided by NASA’s Astrophysics Research and Analysis program, NNH16ZDA001N.

Searching for variable stars in the cores of five metal-rich globular clusters using EMCCD observations

DEFF Research Database (Denmark)

Skottfelt, Jesper; Bramich, D. M.; Jaimes, R. Figuera

2015-01-01

. The observations were made with the electron multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile, and they were analysed using difference image analysis (DIA) to obtain high-precision light curves of the variable stars. It was possible to identify and classify all of the previously...

The Evolution of Cataclysmic Variables as Revealed by Their Donor Stars

Science.gov (United States)

Knigge, Christian; Baraffe, Isabelle; Patterson, Joseph

2011-06-01

We present an attempt to reconstruct the complete evolutionary path followed by cataclysmic variables (CVs), based on the observed mass-radius relationship of their donor stars. Along the way, we update the semi-empirical CV donor sequence presented previously by one of us, present a comprehensive review of the connection between CV evolution and the secondary stars in these systems, and reexamine most of the commonly used magnetic braking (MB) recipes, finding that even conceptually similar ones can differ greatly in both magnitude and functional form. The great advantage of using donor radii to infer mass-transfer and angular-momentum-loss (AML) rates is that they sample the longest accessible timescales and are most likely to represent the true secular (evolutionary average) rates. We show explicitly that if CVs exhibit long-term mass-transfer-rate fluctuations, as is often assumed, the expected variability timescales are so long that other tracers of the mass-transfer rate—including white dwarf (WD) temperatures—become unreliable. We carefully explore how much of the radius difference between CV donors and models of isolated main-sequence stars may be due to mechanisms other than mass loss. The tidal and rotational deformation of Roche-lobe-filling stars produces ~= 4.5% radius inflation below the period gap and ~= 7.9% above. A comparison of stellar models to mass-radius data for non-interacting stars suggests a real offset of ~= 1.5% for fully convective stars (i.e., donors below the gap) and ~= 4.9% for partially radiative ones (donors above the gap). We also show that donor bloating due to irradiation is probably smaller than, and at most comparable to, these effects. After calibrating our models to account for these issues, we fit self-consistent evolution sequences to our compilation of donor masses and radii. In the standard model of CV evolution, AMLs below the period gap are assumed to be driven solely by gravitational radiation (GR), while AMLs

THE EVOLUTION OF CATACLYSMIC VARIABLES AS REVEALED BY THEIR DONOR STARS

International Nuclear Information System (INIS)

Knigge, Christian; Baraffe, Isabelle; Patterson, Joseph

2011-01-01

We present an attempt to reconstruct the complete evolutionary path followed by cataclysmic variables (CVs), based on the observed mass-radius relationship of their donor stars. Along the way, we update the semi-empirical CV donor sequence presented previously by one of us, present a comprehensive review of the connection between CV evolution and the secondary stars in these systems, and reexamine most of the commonly used magnetic braking (MB) recipes, finding that even conceptually similar ones can differ greatly in both magnitude and functional form. The great advantage of using donor radii to infer mass-transfer and angular-momentum-loss (AML) rates is that they sample the longest accessible timescales and are most likely to represent the true secular (evolutionary average) rates. We show explicitly that if CVs exhibit long-term mass-transfer-rate fluctuations, as is often assumed, the expected variability timescales are so long that other tracers of the mass-transfer rate-including white dwarf (WD) temperatures-become unreliable. We carefully explore how much of the radius difference between CV donors and models of isolated main-sequence stars may be due to mechanisms other than mass loss. The tidal and rotational deformation of Roche-lobe-filling stars produces ≅ 4.5% radius inflation below the period gap and ≅ 7.9% above. A comparison of stellar models to mass-radius data for non-interacting stars suggests a real offset of ≅ 1.5% for fully convective stars (i.e., donors below the gap) and ≅ 4.9% for partially radiative ones (donors above the gap). We also show that donor bloating due to irradiation is probably smaller than, and at most comparable to, these effects. After calibrating our models to account for these issues, we fit self-consistent evolution sequences to our compilation of donor masses and radii. In the standard model of CV evolution, AMLs below the period gap are assumed to be driven solely by gravitational radiation (GR), while AMLs

CosmoQuest: Virtual Star Parties as a Conduit to Citizen Science Research

Science.gov (United States)

Lewis, Scott; Gugliucci, N. E.; Gay, P. L.; Amateur Astronomer Team; Commentator Team

2013-01-01

CosmoQuest has created an environment that actively engages the public through online star parties while building a growing virtual research center that allows individuals anywhere in the world to participate in and contribute to scientific research. Utilizing the infrastructure of Google+ and YouTube, CosmoQuest has brought optical observational astronomy into homes across the world. Every week astronomers - amateur and professional - meet to share live sky images and to discuss the science behind their beauty during Virtual Star parties. A wide array of optics and digital detectors from varied locations collaborate in a fashion not possible in the standard public star party. Every viewer is able to virtually look through the imaging telescope simultaneously while the equipment owner doesn’t need to worry about accidental mishandling by the public. Digital cameras and CCDs also allow longer exposures of deep-sky objects, something not typical in a standard star party event. Our diversity of equipment - ranging from hand-guided Dobsonian telescopes to 16” Schmidt-Cassegrain telescopes on Paramounts - give viewers the opportunity to experience the sky through different systems. Additional Star Parties focus on special astronomical events, such as eclipses and transits. The annular eclipse of 20 May, 2012 brought together astronomers, space enthusiasts and a curious public into a Google+ Hangout On Air to celebrate the event while advocating safe observing methods and explaining the science behind the phenomenon. Public photos of the eclipse were shared live in the broadcast while video of the event was streamed for thousands of viewers to enjoy. Other special event star parties have focused on the Super Moon, Eros Opposition, and the Venus Transit. In this poster we review the technology behind star parties and the reach of these events.

Challenges in the automated classification of variable stars in large databases

Directory of Open Access Journals (Sweden)

Graham Matthew

2017-01-01

Full Text Available With ever-increasing numbers of astrophysical transient surveys, new facilities and archives of astronomical time series, time domain astronomy is emerging as a mainstream discipline. However, the sheer volume of data alone - hundreds of observations for hundreds of millions of sources – necessitates advanced statistical and machine learning methodologies for scientific discovery: characterization, categorization, and classification. Whilst these techniques are slowly entering the astronomer’s toolkit, their application to astronomical problems is not without its issues. In this paper, we will review some of the challenges posed by trying to identify variable stars in large data collections, including appropriate feature representations, dealing with uncertainties, establishing ground truths, and simple discrete classes.

New Variable Stars Discovered by Data Mining Images Taken during Recent Asteroid Photometric Observations. II. Results from July 2015 through December 2016

Science.gov (United States)

Papini, R.; Marchini, A.; Salvaggio, F.; Agnetti, D.; Bacci, P.; Banfi, M.; Bianciardi, G.; Collina, M.; Franco, L.; Galli, G.; Milani, M. G. A.; Lopresti, C.; Marino, G.; Rizzuti, L.; Ruocco, N.; Quadri, U.

2017-12-01

This paper follows the previous publication of new variables discovered at Astronomical Observatory, DSFTA, University of Siena, while observing asteroids in order to determine their rotational periods. Usually, this task requires time series images acquisition on a single field for as long as possible on a few nights not necessarily consecutive. Checking continually this "goldmine" allowed us to discover 57 variable stars not yet listed in catalogues or databases. While most of the new variables are eclipsing binaries, a few belong to the RR Lyrae or delta Scuti class. Since asteroid work is definitely a time-consuming activity, coordinated campaigns of follow-up with other observatories have been fundamental in order to determine the elements of the ephemeris and sometimes the right subclass of variability. Further observations of these new variables are therefore strongly encouraged in order to better characterize these stars, especially pulsating ones whose data combined with those taken during professional surveys seem to suggest the presence of light curve amplitude and period variations.

An extremely luminous and variable ultraluminous X-ray source in the outskirts of Circinus observed with NuSTAR

Energy Technology Data Exchange (ETDEWEB)

Walton, D. J.; Fuerst, F.; Harrison, F.; Stern, D.; Grefenstette, B. W.; Madsen, K. K.; Rana, V. [Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States); Bachetti, M.; Barret, D.; Webb, N. A. [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France); Bauer, F. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22 (Chile); Boggs, S. E.; Craig, W. W. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Christensen, F. E. [DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Fabian, A. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Hailey, C. J. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Miller, J. M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Ptak, A.; Zhang, W. W. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2013-12-20

Following a serendipitous detection with the Nuclear Spectroscopic Telescope Array (NuSTAR), we present a multi-epoch spectral and temporal analysis of an extreme ultraluminous X-ray source (ULX) located in the outskirts of the Circinus galaxy, hereafter Circinus ULX5, including coordinated XMM-Newton+NuSTAR follow-up observations. The NuSTAR data presented here represent one of the first instances of a ULX reliably detected at hard (E > 10 keV) X-rays. Circinus ULX5 is variable on long time scales by at least a factor of ∼5 in flux, and was caught in a historically bright state during our 2013 observations (0.3-30.0 keV luminosity of 1.6 × 10{sup 40} erg s{sup –1}). During this epoch, the source displayed a curved 3-10 keV spectrum, broadly similar to other bright ULXs. Although pure thermal models result in a high energy excess in the NuSTAR data, this excess is too weak to be modeled with the disk reflection interpretation previously proposed to explain the 3-10 keV curvature in other ULXs. In addition to flux variability, clear spectral variability is also observed. While in many cases the interpretation of spectral components in ULXs is uncertain, the spectral and temporal properties of all the high quality data sets currently available strongly support a simple disk-corona model reminiscent of that invoked for Galactic binaries, with the accretion disk becoming more prominent as the luminosity increases. However, although the disk temperature and luminosity are well correlated across all time scales currently probed, the observed luminosity follows L∝T {sup 1.70±0.17}, flatter than expected for simple blackbody radiation. The spectral variability displayed here is highly reminiscent of that observed from known Galactic black hole binaries (BHBs) at high luminosities. This comparison implies a black hole mass of ∼90 M {sub ☉} for Circinus ULX5. However, given the diverse behavior observed from Galactic BHB accretion disks, this mass estimate is

Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis

NARCIS (Netherlands)

David-Uraz, A.; Wade, G.A.; Petit, V.; ud-Doula, A.; Sundqvist, J.O.; Grunhut, J.; Schultz, M.; Neiner, C.; Alecian, E.; Henrichs, H.F.; Bouret, J.-C.

2014-01-01

OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations. In this paper, we evaluate the possible relation

Dwarf spheroidal satellites of M31. I. Variable stars and stellar populations in Andromeda XIX

Energy Technology Data Exchange (ETDEWEB)

Cusano, Felice; Clementini, Gisella; Garofalo, Alessia; Federici, Luciana, E-mail: felice.cusano@oabo.inaf.it, E-mail: gisella.clementini@oabo.inaf.it, E-mail: luciana.federici@oabo.inaf.it, E-mail: alessia.garofalo@studio.unibo.it [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); and others

2013-12-10

We present B, V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.'2) of Andromeda's dwarf spheroidal companions, which we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23' × 23' area centered on And XIX and present the deepest color-magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V ∼ 26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which extends to the blue to significantly populate the classical instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and three of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ((P {sub ab}) = 0.62 days, σ = 0.03 days) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average luminosity of the RR Lyrae stars ((V(RR)) = 25.34 mag, σ = 0.10 mag), we determine a distance modulus of (m – M){sub 0} = 24.52 ± 0.23 mag in a scale where the distance to the Large Magellanic Cloud (LMC) is 18.5 ± 0.1 mag. The ACs follow a well-defined Period-Wesenheit (PW) relation that appears to be in very good agreement with the PW relationship defined by the ACs in the LMC.

A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL α CYGNI VARIABLE AND A-TYPE SUPERGIANT STAR DENEB

International Nuclear Information System (INIS)

Richardson, N. D.; Morrison, N. D.; Kryukova, E. E.; Adelman, S. J.

2011-01-01

Deneb is often considered the prototypical A-type supergiant and is one of the visually most luminous stars in the Galaxy. A-type supergiants are potential extragalactic distance indicators, but the variability of these stars needs to be better characterized before this technique can be considered reliable. We analyzed 339 high-resolution echelle spectra of Deneb obtained over the five-year span of 1997 through 2001 as well as 370 Stroemgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the Hα profile, Hα equivalent widths, and radial velocities measured from Si II λλ 6347, 6371. Time-series analysis reveals no obvious cyclic behavior that proceeds through multiple observing seasons, although we found a suspected 40 day period in two, non-consecutive observing seasons. Some correlations are found between photometric and radial velocity data sets and suggest radial pulsations at two epochs. No correlation is found between the variability of the Hα profiles and that of the radial velocities or the photometry. Lucy found evidence that Deneb was a long-period single-lined spectroscopic binary star, but our data set shows no evidence for radial velocity variations caused by a binary companion.

Neutron Stars and NuSTAR

Science.gov (United States)

Bhalerao, Varun

2012-05-01

among all classes of neutron star binaries. Intrigued by this diversity - which points to diverse birth masses - we undertook a systematic survey to measure the masses of neutron stars in nine high-mass X-ray binaries. In this thesis, I present results from this ongoing project. While neutron stars formed the primary focus of my work, I also explored other topics in compact objects. Appendix A describes the discovery and complete characterization of a 1RXS J173006.4+033813, a polar cataclysmic variable. Appendix B describes the discovery of a diamond planet orbiting a millisecond pulsar, and our search for its optical counterpart.

The first spectroscopically confirmed Mira star in M33

Czech Academy of Sciences Publication Activity Database

Barsukova, E.A.; Goranskij, V.P.; Hornoch, Kamil; Fabrika, S.; Pietsch, W.; Sholukhova, O.; Valeev, A.F.

2011-01-01

Roč. 413, č. 3 (2011), s. 1797-1802 ISSN 0035-8711 Institutional research plan: CEZ:AV0Z10030501 Keywords : AGB and post AGB * variables stars * general galaxies Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.900, year: 2011

ULTRA-LOW AMPLITUDE VARIABLES IN THE LARGE MAGELLANIC CLOUD-CLASSICAL CEPHEIDS, POP. II CEPHEIDS, RV TAU STARS, AND BINARY VARIABLES

International Nuclear Information System (INIS)

Robert Buchler, J.; Wood, Peter R.; Soszynski, Igor

2009-01-01

A search for variable stars with ultra-low amplitudes (ULAs), in the millimagnitude range, has been made in the combined MACHO and OGLE databases in the broad vicinity of the Cepheid instability strip in the HR diagram. A total of 25 singly periodic and 4 multiply periodic ULA objects have been uncovered. Our analysis does not allow us to distinguish between pulsational and ellipsoidal (binary) variabilities, nor between Large Magellanic Cloud (LMC) and foreground objects. However, the objects are strongly clustered and appear to be associated with the pulsational instability strips of LMC Pop. I and II variables. When combined with the ULA variables of Buchler et al., a total of 20 objects fall close to the classical Cepheid instability strip. However, they appear to fall on parallel period-magnitude (PM) relations that are shifted to slightly higher magnitude which would confer them a different evolutionary status. Low-amplitude RV Tauri and Pop. II Cepheids have been uncovered that do not appear in the MACHO or OGLE catalogs. Interestingly, a set of binaries seem to lie on a PM relation that is essentially parallel to that of the RV Tauri/Pop. II Cepheids.

A Binary Nature of the Marginal CP Star Sigma Sculptoris

Science.gov (United States)

Janík, Jan; Krtička, Jiří; Mikulášek, Zdeněk; Zverko, Juraj; Pintado, Olga; Paunzen, Ernst; Prvák, Milan; Skalický, Jan; Zejda, Miloslav; Adam, Christian

2018-05-01

The A2 V star σ Scl was suspected of being a low-amplitude rotating variable of the Ap-type star by several authors. Aiming to decide whether the star is a variable chemically peculiar (CP) star, we searched for the photometric and spectroscopic variability, and determined chemical abundances of σ Scl. The possible variability was tested using several types of periodograms applied to the photometry from Long-Term Photometry of Variables project (LTPV) and Hipparcos. Sixty spectrograms of high signal-to-noise (S/N) were obtained and used for chemical analysis of the stellar atmosphere and for looking for spectral variability that is symptomatic for the CP stars. We did not find any signs of the light variability or prominent chemical peculiarity, that is specific for the CP stars. The only exception is the abundance of scandium, which is significantly lower than the solar one and yttrium and barium, which are strongly overabundant. As a by-product of the analysis, and with the addition of 29 further spectra, we found that σ Scl is a single-lined spectroscopic binary with orbital period of 46.877(8) d. We argue that σ Scl is not an Ap star, but rather a marginal Am star in SB1 system. The spectral energy distribution of the binary reveals infrared excess due to circumstellar material.

Infrared Observations of FS CMa Stars

Science.gov (United States)

Sitko, Michael L.; Russell, R. W.; Lynch, D. K.; Grady, C. A.; Hammel, H. B.; Beerman, L. C.; Day, A. N.; Huelsman, D.; Rudy, R. J.; Brafford, S. M.; Halbedel, E. M.

2009-01-01

A subset of non-supergiant B[e] stars has recently been recognized as forming a fairly unique class of objects with very strong emission lines, infrared excesses, and locations not associated with star formation. The exact evolutionary state of these stars, named for the prototype FS CMa, is uncertain, and they have often been classified as isolated Herbig AeBe stars. We present infrared observations of two of these stars, HD 45677 (FS CMa), HD 50138 (MWC 158), and the candidate FS CMa star HD 190073 (V1295 Aql) that span over a decade in time. All three exhibit an emission band at 10 microns due to amorphous silicates, confirming that much (if not all) of the infrared excess is due to dust. HD 50138 is found to exhibit 20% variability between 3-13 microns that resembles that found in pre-main sequence systems (HD 163296 and HD 31648). HD 45677, despite large changes at visual wavelengths, has remained relatively stable in the infrared. To date, no significant changes have been observed in HD 190073. This work is supported in part by NASA Origins of Solar Systems grant NAG5-9475, NASA Astrophysics Data Program contract NNH05CD30C, and the Independent Research and Development program at The Aerospace Corporation.

Computing the Polarimetric and Photometric Variability of Be Stars

Science.gov (United States)

Marr, K. C.; Jones, C. E.; Halonen, R. J.

2018-01-01

We investigate variations in the linear polarization as well as in the V-band and B-band color–magnitudes for classical Be star disks. We present two models: disks with enhanced disk density and disks that are tilted or warped from the stellar equatorial plane. In both cases, we predict variation in observable properties of the system as the disk rotates. We use a non-LTE radiative transfer code BEDISK (Sigut & Jones) in combination with a Monte Carlo routine that includes multiple scattering (Halonen et al.) to model classical Be star systems. We find that a disk with an enhanced density region that is one order of magnitude denser than the disk’s base density shows as much as ∼ 0.2 % variability in the polarization while the polarization position angle varies by ∼ 8^\\circ . The ΔV magnitude for the same system shows variations of up to ∼ 0.4 mag while the Δ(B–V) color varies by at most ∼ 0.01 mag. We find that disks tilted from the equatorial plane at small angles of ∼ 30^\\circ more strongly reflect the values of polarization and color–magnitudes reported in the literature than disks tilted at larger angles. For this model, the linear polarization varies by ∼ 0.3 % , the polarization position angle varies by ∼ 60^\\circ , the ΔV magnitude varies up to 0.35 mag, and the Δ(B–V) color varies by up to 0.1 mag. We find that the enhanced disk density models show ranges of polarization and color–magnitudes that are commensurate with what is reported in the literature for all sizes of the density-enhanced regions. From this, we cannot determine any preference for small or large density-enhanced regions.

Models of symbiotic stars

Science.gov (United States)

Friedjung, Michael

1993-01-01

One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical

Classification of Ap-stars HR 830 and ZI CVn

International Nuclear Information System (INIS)

Zverko, J.

1984-01-01

Two ambiguously classified Ap-stars, HR 830 and 21 CVn, are studied. The observational data are compared with the data for normal stars αDel and αLyr. Star HR 830 is classified as Ap of type Si based on the enhanced absorption in the Si lines and photometric variability in UBV. 21 CVn is classified as Ap Si based on weaker absorption of helium, the variability of helium lines, photometric periodic variability and the properties of the UV spectrum. It is concluded that the photometric periodic variability is a good indicator of Ap-properties of rapidly rotating A and late B stars. (author)

Stars and Flowers, Flowers and Stars

Science.gov (United States)

Minti, Hari

2012-12-01

The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

STAR: Software Toolkit for Analysis Research

International Nuclear Information System (INIS)

Doak, J.E.; Prommel, J.M.; Whiteson, R.; Hoffbauer, B.L.; Thomas, T.R.; Helman, P.

1993-01-01

Analyzing vast quantities of data from diverse information sources is an increasingly important element for nonproliferation and arms control analysis. Much of the work in this area has used human analysts to assimilate, integrate, and interpret complex information gathered from various sources. With the advent of fast computers, we now have the capability to automate this process thereby shifting this burden away from humans. In addition, there now exist huge data storage capabilities which have made it possible to formulate large integrated databases comprising many thereabouts of information spanning a variety of subjects. We are currently designing a Software Toolkit for Analysis Research (STAR) to address these issues. The goal of STAR is to Produce a research tool that facilitates the development and interchange of algorithms for locating phenomena of interest to nonproliferation and arms control experts. One major component deals with the preparation of information. The ability to manage and effectively transform raw data into a meaningful form is a prerequisite for analysis by any methodology. The relevant information to be analyzed can be either unstructured text structured data, signals, or images. Text can be numerical and/or character, stored in raw data files, databases, streams of bytes, or compressed into bits in formats ranging from fixed, to character-delimited, to a count followed by content The data can be analyzed in real-time or batch mode. Once the data are preprocessed, different analysis techniques can be applied. Some are built using expert knowledge. Others are trained using data collected over a period of time. Currently, we are considering three classes of analyzers for use in our software toolkit: (1) traditional machine learning techniques, (2) the purely statistical system, and (3) expert systems

Astronomy Education Research Observations from the iSTAR international Study of Astronomical Reasoning Database

Science.gov (United States)

Tatge, C. B.; Slater, S. J.; Slater, T. F.; Schleigh, S.; McKinnon, D.

2016-12-01

Historically, an important part of the scientific research cycle is to situate any research project within the landscape of the existing scientific literature. In the field of discipline-based astronomy education research, grappling with the existing literature base has proven difficult because of the difficulty in obtaining research reports from around the world, particularly early ones. In order to better survey and efficiently utilize the wide and fractured range and domain of astronomy education research methods and results, the iSTAR international Study of Astronomical Reasoning database project was initiated. The project aims to host a living, online repository of dissertations, theses, journal articles, and grey literature resources to serve the world's discipline-based astronomy education research community. The first domain of research artifacts ingested into the iSTAR database were doctoral dissertations. To the authors' great surprise, nearly 300 astronomy education research dissertations were found from the last 100-years. Few, if any, of the literature reviews from recent astronomy education dissertations surveyed even come close to summarizing this many dissertations, most of which have not been published in traditional journals, as re-publishing one's dissertation research as a journal article was not a widespread custom in the education research community until recently. A survey of the iSTAR database dissertations reveals that the vast majority of work has been largely quantitative in nature until the last decade. We also observe that modern-era astronomy education research writings reaches as far back as 1923 and that the majority of dissertations come from the same eight institutions. Moreover, most of the astronomy education research work has been done covering learners' grasp of broad knowledge of astronomy rather than delving into specific learning targets, which has been more in vogue during the last two decades. The surprisingly wide breadth

The dance of the double stars

International Nuclear Information System (INIS)

Theokas, A.

1985-01-01

The paper concerns pairs of stars orbiting one another. The evolutionary path model for close binary stars, involving a mass transfer of gases between the stars, is described. The life history of a single star; cataclysmic variables; the algol paradox, matter and lagranges' point; x-ray binaries and bursters; and pulsars; are all briefly discussed. (U.K.)

Galactic archaeology for amateur astronomers: RR Lyrae stars as tracers of the Milky Way formation

Science.gov (United States)

Carballo-Bello, Julio A.; Martínez-Delgado, David; Fliri, Jürgen

2011-06-01

Cosmological models predict that large galaxies like the Milky Way formed from the accretion of smaller stellar systems. The most spectacular of these merger events are stellar tidal streams, rivers of stars and dark matter that envelop the discs of spiral galaxies. We present a research project for a collaboration with amateur astronomers in the study of the formation process of our Galaxy. The main objective is the search for RR Lyrae variable stars in the known stellar streams (Sagitarius, Monoceros, Orphan, etc) a project that can be carried out using small telescopes. The catalogue of candidate variable stars were selected from SDSS data based in colour criteria and it will be sent to interested amateur astronomers who wish to participate in scientific research in one of the most active and competitive topics in Galactic astronomy.

Photometric Variability of Four Coronally Active Stars J. C. Pandey ...

Indian Academy of Sciences (India)

R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

ray surveys with the Einstein and the ROSAT observatories and found to be associated with bright late- type stars. Many of these stars have not been studied in detail for their chromospheric and coronal activity, and their nature is not fully ...

An Application of Supervised Learning Methods to Search for Variable Stars in a Selected Field of the VVV Survey

Science.gov (United States)

Rodríguez-Feliciano, B.; García-Varela, A.; Pérez-Ortiz, M. F.; Sabogal, B. E.; Minniti, D.

2017-07-01

We characterize properties of time series of variable stars in the B278 field of the VVV survey, using robust statistics. Using random forest and support vector machines classifiers we propose 47 candidates to RR Lyraae, and 12 candidates to WU Ursae Majoris eclipsing binaries.

Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and δ Scuti stars

Directory of Open Access Journals (Sweden)

Arias J.P.Sánchez

2017-01-01

Full Text Available We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification.

PERIODIC VARIABILITY OF LOW-MASS STARS IN SLOAN DIGITAL SKY SURVEY STRIPE 82

International Nuclear Information System (INIS)

Becker, A. C.; Hawley, S. L.; Ivezic, Z.; Kowalski, A. F.; Sesar, B.; Bochanski, J. J.; West, A. A.

2011-01-01

We present a catalog of periodic stellar variability in the 'Stripe 82' region of the Sloan Digital Sky Survey. After aggregating and re-calibrating catalog-level data from the survey, we ran a period-finding algorithm (Supersmoother) on all point-source light curves. We used color selection to identify systems that are likely to contain low-mass stars, in particular M dwarfs and white dwarfs. In total, we found 207 candidates, the vast majority of which appear to be in eclipsing binary systems. The catalog described in this paper includes 42 candidate M dwarf/white dwarf pairs, four white dwarf pairs, 59 systems whose colors indicate they are composed of two M dwarfs and whose light-curve shapes suggest they are in detached eclipsing binaries, and 28 M dwarf systems whose light-curve shapes suggest they are in contact binaries. We find no detached systems with periods longer than 3 days, thus the majority of our sources are likely to have experienced orbital spin-up and enhanced magnetic activity. Indeed, 26 of 27 M dwarf systems that we have spectra for show signs of chromospheric magnetic activity, far higher than the 24% seen in field stars of the same spectral type. We also find binaries composed of stars that bracket the expected boundary between partially and fully convective interiors, which will allow the measurement of the stellar mass-radius relationship across this transition. The majority of our contact systems have short orbital periods, with small variance (0.02 days) in the sample near the observed cutoff of 0.22 days. The accumulation of these stars at short orbital period suggests that the process of angular momentum loss, leading to period evolution, becomes less efficient at short periods. These short-period systems are in a novel regime for studying the effects of orbital spin-up and enhanced magnetic activity, which are thought to be the source of discrepancies between mass-radius predictions and measurements of these properties in eclipsing

Spectrophotometry of emission-line stars in the magellanic clouds

Science.gov (United States)

Bohannan, Bruce

1990-01-01

The strong emission lines in the most luminous stars in the Magellanic Clouds indicate that these stars have such strong stellar winds that their photospheres are so masked that optical absorption lines do not provide an accurate measure of photospheric conditions. In the research funded by this grant, temperatures and gravities of emission-line stars both in the Large (LMC) and Small Magellanic Clouds (SMC) have been measured by fitting of continuum ultraviolet-optical fluxes observed with IUE with theoretical model atmospheres. Preliminary results from this work formed a major part of an invited review 'The Distribution of Types of Luminous Blue Variables'. Interpretation of the IUE observations obtained in this grant and archive data were also included in a talk at the First Boulder-Munich Hot Stars Workshop. Final results of these studies are now being completed for publication in refereed journals.

BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. II. MODELING THE CENTRAL STARS OF NGC 6026 AND NGC 6337

International Nuclear Information System (INIS)

Hillwig, Todd C.; Bond, Howard E.; Afsar, Melike; De Marco, Orsola

2010-01-01

Close-binary central stars of planetary nebulae (CSPNe) provide an opportunity to explore the evolution of PNe, their shaping, and the evolution of binary systems undergoing a common-envelope phase. Here, we present the results of time-resolved photometry of the binary central stars (CSs) of the PNe NGC 6026 and NGC 6337 as well as time-resolved spectroscopy of the CS of NGC 6026. The results of a period analysis give an orbital period of 0.528086(4) days for NGC 6026 and a photometric period of 0.1734742(5) days for NGC 6337. In the case of NGC 6337, it appears that the photometric period reflects the orbital period and that the variability is the result of the irradiated hemisphere of a cool companion. The inclination of the thin PN ring is nearly face-on. Our modeled inclination range for the close central binary includes nearly face-on alignments and provides evidence for a direct binary-nebular shaping connection. For NGC 6026, however, the radial-velocity curve shows that the orbital period is twice the photometric period. In this case, the photometric variability is due to an ellipsoidal effect in which the CS nearly fills its Roche lobe and the companion is most likely a hot white dwarf. NGC 6026 then is the third PN with a confirmed central binary where the companion is compact. Based on the data and modeling using a Wilson-Devinney code, we discuss the physical parameters of the two systems and how they relate to the known sample of close-binary CSs, which comprise 15%-20% of all PNe.

Photoelectric photometry of the Am star HR = V423 Per

International Nuclear Information System (INIS)

Jerzykiewicz, M.

1989-01-01

This spectroscopic binary is the largest amplitude variable among Am stars. UBV observations of the star are presented. They show that in 1964 and 1965 it was constant in B and was only marginally variable in U. The hypothesis of the ellipsoidal variability of HR 976 is then discussed and found untenable. It is pointed out that this result may reopen the issue of light variability of Am stars. 10 refs., 2 figs., 2 tabs. (author)

The symbiotic star H1-36

International Nuclear Information System (INIS)

Allen, D.A.

1983-01-01

Optical and infrared spectrophotometry is presented of the high-excitation emission-line star H1-36. The presence of a variable M giant is established: H1-36 may therefore be classified as a symbiotic star. The observations are interpreted in terms of the usual binary model for symbiotic stars, namely that an unseen star is heated by accretion of gas from its companion M giant. (author)

Using nonradial pulsations to determine the envelope composition of very evolved stars

International Nuclear Information System (INIS)

Starrfield, S.

1986-01-01

Recent observational and theoretical studies of the ZZ Ceti variables (DA degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (DO degenerate dwarfs) have shown them to be pulsating in nonradial g + -modes. The pulsation mechanism has been identified for each class of variable star and, in all cases, involves predictions of the stars envelope composition. The ZZ Ceti variables must have pure hydrogen surface layers, the DBV stars must have pure helium surface layers, and the GW Vir stars must have carbon and oxygen rich surface layers. 44 refs

The Globular Cluster NGC 6402 (M14). II. Variable Stars

DEFF Research Database (Denmark)

Contreras Peña, C.; Catelan, M.; Grundahl, F.

2018-01-01

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. By considering all of the RR Lyrae stars as members of the cluster, we derive =0.589 {{d...

Investigations of cataclysmic variables by ESA INTEGRAL

Czech Academy of Sciences Publication Activity Database

Hudec, René; Blažek, Martin

2012-01-01

Roč. 83, č. 2 (2012), s. 659-664 ISSN 0037-8720. [Workshop on the golden age of cataclysmic variables and related objects /2./. Palermo , 09.09.2013-14.09.2013] R&D Projects: GA ČR GA205/08/1207 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * high-energy sources * cataclysmic variables Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

Halo star streams in the solar neighborhood

NARCIS (Netherlands)

Kepley, Amanda A.; Morrison, Heather L.; Helmi, Amina; Kinman, T. D.; Van Duyne, Jeffrey; Martin, John C.; Harding, Paul; Norris, John E.; Freeman, Kenneth C.

2007-01-01

We have assembled a sample of halo stars in the solar neighborhood to look for halo substructure in velocity and angular momentum space. Our sample ( 231 stars) includes red giants, RR Lyrae variable stars, and red horizontal branch stars within 2.5 kpc of the Sun with [Fe/H] less than -1.0. It was

Pulsations of delta Scuti stars

International Nuclear Information System (INIS)

Cox, A.N.

1990-01-01

In this paper the authors give a general review of the pulsating δ Scuti variables, including the observed light curves and positions of the stars in the Hertzsprung-Russell diagram. Theoretical interpretations from evolution and pulsation calculations give their masses, radii, luminosities, and even their approximate internal compositions. Then we discuss three models of these stars, and use them to study the nonlinear hydrodynamic behavior of these stars, after which the authors outline the hydrodynamic equations and the Stellingwerf method for obtaining strictly periodic solutions. The authors also present the problems of allowing for time-dependent convection and its great sensitivity to temperature and density. Tentative results to data do not show any tendency for amplitudes to grow to large unobserved amplitudes, in disagreement with an earlier suggestion by Stellingwerf. Finally, the authors find that the very small growth rates of the pulsations may even be too small to be useful in seeking a periodic solution. The δ Scuti variables are the most common type of variable star in our galaxy except for the white dwarfs. This is because stars in the mass range from just over one M circle-dot up to at least several M circle-dot pass through the yellow giant instability strip in the Hertzsprung-Russell diagram as they evolve off the main sequence to the red. Actually, stars up to the maximum main sequence mass also evolve through this region at higher luminosities, but there are so few of them, and they evolve so rapidly to the red, that they are almost unknown. At the higher luminosity, they probably would be called first-instability strip-crossing Cepheids anyway. Such cepheids are difficult to separate from those that are on the second blueward instability strip crossing that is much slower. Really, the δ Scuti variables are just low-luminosity Cepheids

The Soft State of Cygnus X-1 Observed With NuSTAR: A Variable Corona and a Stable Inner Disk

DEFF Research Database (Denmark)

Walton, D. J.; Tomsick, J. A.; Madsen, K. K.

2016-01-01

We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state based on four observations with the Nuclear Spectroscopic Telescope Array (NuSTAR). Despite the basic similarity of the observed spectra, there is clear spectral variability between epochs. To investigate this variabilit...

Mythical Maia, ultrashort and 53 PSC variables. Lecture 4

International Nuclear Information System (INIS)

Cox, A.N.

1983-01-01

Moving down the main sequence from the #betta# Cephei variables, we come to later B-type stars. The suspicion of variability for these stars goes back to Vogel in 1891 who studied the radial velocities of Vega. Since that time there have been numerous studies of Vega (Wisniewski and Johnson 1979, Fernie 1981) and other B and early A stars which hint at variability in both radial velocity and light. Since Struve (1955) discussed these stars 28 years ago, they have been called the Maia stars after the Pleiades star that he thought was the prototype. The uncertainty in their actual variability has led Breger (1980) to call them the mythical Maia variables

HDE 229189 - A variable Ae star in the field of NGC 6910

International Nuclear Information System (INIS)

Halbedel, E.M.

1991-01-01

The star HDE 229189 (BD + 40 4145; in the field, though probably not a member, of the open cluster NGC 6910) has been found to exhibit large photometric changes in V magnitude over relatively short time scales. The total observed range was 0.416 V magnitude. An outburst in 1982 showed an even greater V range (Delta V = 1.66) and concomitant color changes. A coude spectrum of the star taken a week before a minor outburst showed emission at H-alpha but no other unusual lines. The star is likely an A3 (V)e star, an unusual object in itself (since stars as late as A3 seldom show emission at H-α), or else possibly a member of a binary system undergoing mass transfer between the members. 19 refs

Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28° 2561

OpenAIRE

Wade, G. A.; Barba, R. H.; Grunhut, J.; Martins, F.; Petit, V.; Sundqvist, J. O.; Townsend, R. H. D.; Walborn, N. R.; Alecian, E.; Alfaro, E. J.; Maíz Apellaniz, J; Arias, Julia Ines; Gamen, Roberto Claudio; Morrell, Nidia Irene; Naze, Y.

2017-01-01

We report magnetic and spectroscopic observations and modelling of the Of?p star CPD −28° 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High-resolution spectropolarimetric data analysed using least-squares deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to ph...

Chemical evolution, stellar nucleosynthesis and a variable star formation rate

International Nuclear Information System (INIS)

Olive, K.A.; Thielemann, F.K.; Truran, J.W.

1986-04-01

The effects of a decreasing star formation rate (SFR) on the galactic abundances of elements produced in massive stars (M ≥ 10 Msub solar). On the basis of a straightforward model of galactic evolution, a relation between the upper mass limit of type II supernovae (M/sub SN/) contributing to chemical evolution and the decline of the SFR (tau) is derived, when the oxygen abundance is determined only by massive stars. The additional requirement that all intermediate mass elements (Ne-Ti), which are also predominantly due to nucleosynthesis in massive stars, are produced in solar proportions leads to a unique value of M/sub SN/ and tau. The application of this method with abundance yields from Arnett (1978) and Woosley and Weaver (1986) resuults, however, in contradicting solutions: M/sub SN/ ≅ 45 Msub solar, tau = ∞, and M/sub SN/ ≅ 15 Msub solar, tau = 3 x 10 9 y. Thus, in order that this approach provide an effective probe of the SFR over the history of our galaxy it is essential that converging and more accurate predictions of the consequences of stellar and supernova nucleosynthesis will be forthcoming. 54 refs., 2 figs., 2 tabs

Massive stars and miniature robots: today's research and tomorrow's technologies

Science.gov (United States)

Taylor, William David

2013-03-01

This thesis documents the reduction of the VLT-FLAMES Tarantula Survey (VFTS) data set, whilst also describing the analysis for one of the serendipitous discoveries: the massive binary R139. This high-mass binary will provide an excellent future calibration point for stellar models, in part as it seems to defy certain expectations about its evolution. Out with the VFTS, a search for binary companions around a trio of B-type supergiants is presented. These stars are surrounded by nebulae that closely resemble the triple-ring structure associated with the poorly-understood SN1987A. Do these stars share a similar evolutionary fate? While strong evidence is found for periodic pulsations in one of the stars, there appears to be no indication of a short-period binary companion suggested in the literature. Gathering observations from a wide range of environments builds a fuller picture of massive stars, but the samples remain somewhat limited. The coming generation of extremely large telescopes will open new regions for studies like the VFTS. Fully utilising these remarkable telescopes will require many new technologies, and this thesis presents one such development project. For adaptive-optics corrected, multi-object instruments it will be necessary to position small pick-off mirrors in the telescope¿s focal plane to select the sub-fields on the sky. This could be most efficiently achieved if the mirrors were self-propelled, which has led to a miniature robot project called MAPS - the Micro Autonomous Positioning System. A number of robots have been built with a footprint of only 30 x 30mm. These wirelessly-controlled robots draw their power from the floor on which they operate and have shown the potential to be positioned to an accuracy of tens of microns. This thesis details much of the early design work and testing of the robots, and also the development of the camera imaging system used to determine the position of the robots. The MAPS project is ongoing and a

Studying coherent scattering in the CP stars atmospheres

Science.gov (United States)

Fišák, J.; Kubát, J.; Krtička, J.

2018-01-01

Chemically peculiar stars form a very interesting class of stars which frequently show variability. The variability is probably caused by the uneven surface distribution of chemical elements. Some elements are overabundant and some elements are underabundant compared to the solar chemical composition. In the case of chemically overabundant composition some of the rare photon-atom processes can be more important than in the atmospheres of stars with solar chemical composition. We study the importance of Rayleigh scattering by helium.

The nature of OH/IR stars

International Nuclear Information System (INIS)

Herman, J.

1983-01-01

In this work masers in evolved stars are studied, in particular the emission from the OH radical. The time variability of the OH masers was measured over a period of five years with the Dwingeloo Radio Telescope. These single-dish observations proved that most of the underlying stars are very long period variables, apparently a kind of extension of the well-known long period Mira variables. The mean OH fluxes and epochs were obtained as well as a confirmation of the radiative coupling between the maser and the star (by comparison with infrared data provided by other observers), the degree of saturation, and, most important of all, a determination of the linear dimensions of the circumstellar shells. Multi-element interferometer observations were made in order to study the spatial structure of OH masers. By combining the phase lag measurements and the spatial extent distances to individual stars could be determined with a high, unprecedented accuracy. Infrared broad-band photometry was done in the wavelength region from 3 μm to 20 μm, where most of the energy of these objects is radiated. The space density and galactic distribution of OH/IR stars are discussed and compared with the appearance of OH masers in the solar neighbourhood. (Auth.)

An infrared diagnostic for magnetism in hot stars

Science.gov (United States)

Oksala, M. E.; Grunhut, J. H.; Kraus, M.; Borges Fernandes, M.; Neiner, C.; Condori, C. A. H.; Campagnolo, J. C. N.; Souza, T. B.

2015-06-01

Magnetospheric observational proxies are used for indirect detection of magnetic fields in hot stars in the X-ray, UV, optical, and radio wavelength ranges. To determine the viability of infrared (IR) hydrogen recombination lines as a magnetic diagnostic for these stars, we have obtained low-resolution (R~ 1200), near-IR spectra of the known magnetic B2V stars HR 5907 and HR 7355, taken with the Ohio State Infrared Imager/Spectrometer (OSIRIS) attached to the 4.1 m Southern Astrophysical Research (SOAR) Telescope. Both stars show definite variable emission features in IR hydrogen lines of the Brackett series, with similar properties as those found in optical spectra, including the derived location of the detected magnetospheric plasma. These features also have the added advantage of a lowered contribution of stellar flux at these wavelengths, making circumstellar material more easily detectable. IR diagnostics will be useful for the future study of magnetic hot stars, to detect and analyze lower-density environments, and to detect magnetic candidates in areas obscured from UV and optical observations, increasing the number of known magnetic stars to determine basic formation properties and investigate the origin of their magnetic fields. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

PERIODIC AND APERIODIC VARIABILITY IN THE MOLECULAR CLOUD ρ OPHIUCHUS

International Nuclear Information System (INIS)

Parks, J. Robert; Plavchan, Peter; Gee, Alan H.; White, Russel J.

2014-01-01

Presented are the results of a near-IR photometric survey of 1678 stars in the direction of the ρ Ophiuchus (ρ Oph) star forming region using data from the 2MASS Calibration Database. For each target in this sample, up to 1584 individual J-, H-, and K s -band photometric measurements with a cadence of ∼1 day are obtained over three observing seasons spanning ∼2.5 yr; it is the most intensive survey of stars in this region to date. This survey identifies 101 variable stars with ΔK s -band amplitudes from 0.044 to 2.31 mag and Δ(J – K s ) color amplitudes ranging from 0.053 to 1.47 mag. Of the 72 young ρ Oph star cluster members included in this survey, 79% are variable; in addition, 22 variable stars are identified as candidate members. Based on the temporal behavior of the K s time-series, the variability is distinguished as either periodic, long time-scale or irregular. This temporal behavior coupled with the behavior of stellar colors is used to assign a dominant variability mechanism. A new period-searching algorithm finds periodic signals in 32 variable stars with periods between 0.49 to 92 days. The chief mechanism driving the periodic variability for 18 stars is rotational modulation of cool starspots while 3 periodically vary due to accretion-induced hot spots. The time-series for six variable stars contains discrete periodic ''eclipse-like'' features with periods ranging from 3 to 8 days. These features may be asymmetries in the circumstellar disk, potentially sustained or driven by a proto-planet at or near the co-rotation radius. Aperiodic, long time-scale variations in stellar flux are identified in the time-series for 31 variable stars with time-scales ranging from 64 to 790 days. The chief mechanism driving long time-scale variability is variable extinction or mass accretion rates. The majority of the variable stars (40) exhibit sporadic, aperiodic variability over no discernable time-scale. No chief variability mechanism

PERIODIC AND APERIODIC VARIABILITY IN THE MOLECULAR CLOUD ρ OPHIUCHUS

Energy Technology Data Exchange (ETDEWEB)

Parks, J. Robert; Plavchan, Peter; Gee, Alan H. [Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 100-22, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); White, Russel J., E-mail: parksj@chara.gsu.edu [Georgia State University, Department of Physics and Astronomy, 25 Park Place, Room 605, Atlanta, GA 30303 (United States)

2014-03-01

Presented are the results of a near-IR photometric survey of 1678 stars in the direction of the ρ Ophiuchus (ρ Oph) star forming region using data from the 2MASS Calibration Database. For each target in this sample, up to 1584 individual J-, H-, and K{sub s} -band photometric measurements with a cadence of ∼1 day are obtained over three observing seasons spanning ∼2.5 yr; it is the most intensive survey of stars in this region to date. This survey identifies 101 variable stars with ΔK{sub s} -band amplitudes from 0.044 to 2.31 mag and Δ(J – K{sub s} ) color amplitudes ranging from 0.053 to 1.47 mag. Of the 72 young ρ Oph star cluster members included in this survey, 79% are variable; in addition, 22 variable stars are identified as candidate members. Based on the temporal behavior of the K{sub s} time-series, the variability is distinguished as either periodic, long time-scale or irregular. This temporal behavior coupled with the behavior of stellar colors is used to assign a dominant variability mechanism. A new period-searching algorithm finds periodic signals in 32 variable stars with periods between 0.49 to 92 days. The chief mechanism driving the periodic variability for 18 stars is rotational modulation of cool starspots while 3 periodically vary due to accretion-induced hot spots. The time-series for six variable stars contains discrete periodic ''eclipse-like'' features with periods ranging from 3 to 8 days. These features may be asymmetries in the circumstellar disk, potentially sustained or driven by a proto-planet at or near the co-rotation radius. Aperiodic, long time-scale variations in stellar flux are identified in the time-series for 31 variable stars with time-scales ranging from 64 to 790 days. The chief mechanism driving long time-scale variability is variable extinction or mass accretion rates. The majority of the variable stars (40) exhibit sporadic, aperiodic variability over no discernable time-scale. No chief

Shooting stars

International Nuclear Information System (INIS)

Maurette, M.; Hammer, C.

1985-01-01

A shooting star passage -even a star shower- can be sometimes easily seen during moonless black night. They represent the partial volatilization in earth atmosphere of meteorites or micrometeorites reduced in cosmic dusts. Everywhere on earth, these star dusts are searched to be gathered. This research made one year ago on the Greenland ice-cap is this article object; orbit gathering projects are also presented [fr

CCD Photometry Using Multiple Comparison Stars

Directory of Open Access Journals (Sweden)

Yonggi Kim

2004-09-01

Full Text Available The accuracy of CCD observations obtained at the Korean 1.8 m telescope has been studied. Seventeen comparison stars in the vicinity of the cataclysmic variable BG CMi have been measured. The ``artificial" star has been used instead of the ``control" star, what made possible to increase accuracy estimates by a factor of 1.3-2.1 times for ``good" and ``cloudy" nights, respectively. The algorithm of iterative determination of accuracy and weights of few comparison stars contributing to the artificial star, has been presented. The accuracy estimates for 13-mag stars are around 0.002 m mag for exposure times of 30 sec.

A HIGH-PRECISION NEAR-INFRARED SURVEY FOR RADIAL VELOCITY VARIABLE LOW-MASS STARS USING CSHELL AND A METHANE GAS CELL

International Nuclear Information System (INIS)

Gagné, Jonathan; Plavchan, Peter; Gao, Peter; Anglada-Escude, Guillem; Furlan, Elise; Brinkworth, Carolyn; Ciardi, David R.; Davison, Cassy; Henry, Todd J.; White, Russel; Tanner, Angelle; Riedel, Adric R.; Latham, David; Johnson, John A.; Bottom, Michael; Mills, Sean; Beichman, Chas; Wallace, Kent; Mennesson, Bertrand; Von Braun, Kaspar

2016-01-01

We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2–M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25–150 Myr) moving groups, the young field star ε Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8–15 m s −1 with a long-term stability of 15–50 m s −1 over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25–50 m s −1 at ≈2.3125 μ m, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3 σ –5 σ . Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s −1 in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.

Pulsating red variables

International Nuclear Information System (INIS)

Whitelock, P.A.

1990-01-01

The observational characteristics of pulsating red variables are reviewed with particular emphasis on the Miras. These variables represent the last stage in the evolution of stars on the Asymptotic Giant Branch (AGB). A large fraction of the IRAS sources in the Bulge are Mira variables and a subset of these are also OH/IR sources. Their periods range up to 720 days, though most are between 360 and 560 days. At a given period those stars with the highest pulsation amplitudes have the highest mass-loss rates; this is interpreted as evidence for a causal connection between mass-loss and pulsation. It is suggested that once an AGB star has become a Mira it will evolve with increasing pulsation amplitude and mass-loss, but with very little change of luminosity or logarithmic period. 26 refs

Discovery of a Group of Receding, Variable Halo Stars toward Norma

Energy Technology Data Exchange (ETDEWEB)

Chakrabarti, Sukanya; Sargent, Benjamin; Lipnicky, Andrew [School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623 (United States); Angeloni, Rodolfo [Departamento de Fisica y Astronomia, Universidad de La Serena, Av. Juan Cisternas 1200 N, La Serena (Chile); Freeman, Kenneth [Research School of Astronomy and Astrophysics ANU RSAA Mount Stromlo Observatory (Australia); Simon, Joshua D. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Konorski, Piotr [Warsaw University Observatory, al. Ujazdowskie 4, 00-001 Warszawa (Poland); Gieren, Wolfgang [Universidad de Concepcion, Concepción, Bío Bío Region (Chile); Sesar, Branimir [Max-Planck Institute for Astronomy, Room 332, Könighstuhl 17, D-69117 Heidelberg (Germany); Blitz, Leo; Basri, Gibor [Department of Astronomy, Campbell Hall, #501, Berkeley, CA 94720 (United States); Vacca, William [SOFIA-USRA, NASA Ames Research Center, Mail Stop N232-12, Moffet Field, CA 94035-1000 (United States); Marengo, Massimo [Department of Physics and Astronomy, Iowa State University, Ames, IA 50010 (United States); Guhathakurta, Puragra [Department of Astronomy, UC Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Quillen, Alice [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Chang, Philip, E-mail: chakrabarti@astro.rit.edu [Dept of Physics, PO Box 413, Milwaukee, WI 53201 (United States)

2017-08-01

We present results from spectroscopic observations of a trio of Cepheid candidates identified from K {sub s} -band light curves toward Norma. The spectra show that these stars are moving with a large and similar radial velocity—the heliocentric velocities are 171 ± 32 km s{sup −1}, 164 ± 37 km s{sup −1}, and 173 ± 20 km s{sup −1}. The average radial velocity is ∼169 km s{sup −1}, which is large and distinct from typical stars in the Galaxy’s stellar disk. Given the radial velocities and associated 1 σ error, we find that the combined probability that these three stars are foreground Milky Way disk stars is ∼7 × 10{sup −4}%, and the probability that these are large-amplitude spotted stars in a binary is ∼10{sup −5}%. These objects at l ∼ 333° and b ∼ −1° are therefore associated with the stellar halo. The identification of these sources as Type I Cepheids is not certain, and thus the distances of these sources are not yet well established. Assuming the 3.6 μ m period–luminosity relation of Type I Cepheids gives a distance of ∼78 kpc for these sources.

Discovery of a Group of Receding, Variable Halo Stars toward Norma

International Nuclear Information System (INIS)

Chakrabarti, Sukanya; Sargent, Benjamin; Lipnicky, Andrew; Angeloni, Rodolfo; Freeman, Kenneth; Simon, Joshua D.; Konorski, Piotr; Gieren, Wolfgang; Sesar, Branimir; Blitz, Leo; Basri, Gibor; Vacca, William; Marengo, Massimo; Guhathakurta, Puragra; Quillen, Alice; Chang, Philip

2017-01-01

We present results from spectroscopic observations of a trio of Cepheid candidates identified from K s -band light curves toward Norma. The spectra show that these stars are moving with a large and similar radial velocity—the heliocentric velocities are 171 ± 32 km s −1 , 164 ± 37 km s −1 , and 173 ± 20 km s −1 . The average radial velocity is ∼169 km s −1 , which is large and distinct from typical stars in the Galaxy’s stellar disk. Given the radial velocities and associated 1 σ error, we find that the combined probability that these three stars are foreground Milky Way disk stars is ∼7 × 10 −4 %, and the probability that these are large-amplitude spotted stars in a binary is ∼10 −5 %. These objects at l ∼ 333° and b ∼ −1° are therefore associated with the stellar halo. The identification of these sources as Type I Cepheids is not certain, and thus the distances of these sources are not yet well established. Assuming the 3.6 μ m period–luminosity relation of Type I Cepheids gives a distance of ∼78 kpc for these sources.

On detecting variables using ROTSE-IIId archival data

Science.gov (United States)

Yesilyaprak, C.; Yerli, S. K.; Aksaker, N.; Gucsav, B. B.; Kiziloglu, U.; Dikicioglu, E.; Coker, D.; Aydin, E.; Ozeren, F. F.

ROTSE (Robotic Optical Transient Search Experiment) telescopes can also be used for variable star detection. As explained in the system description tep{2003PASP..115..132A}, they have a good sky coverage and they allow a fast data acquisition. The optical magnitude range varies between 7^m to 19^m. Thirty percent of the telescope time of north-eastern leg of the network, namely ROTSE-IIId (located at TUBITAK National Observatory, Bakirlitepe, Turkey http://www.tug.tubitak.gov.tr/) is owned by Turkish researchers. Since its first light (May 2004) considerably a large amount of data has been collected (around 2 TB) from the Turkish time and roughly one million objects have been identified from the reduced data. A robust pipeline has been constructed to discover new variables, transients and planetary nebulae from this archival data. In the detection process, different statistical methods were applied to the archive. We have detected thousands of variable stars by applying roughly four different tests to light curve of each star. In this work a summary of the pipeline is presented. It uses a high performance computing (HPC) algorithm which performs inhomogeneous ensemble photometry of the data on a 36 core cluster. This study is supported by TUBITAK (Scientific and Technological Research Council of Turkey) with the grant number TBAG-108T475.

Star identification methods, techniques and algorithms

CERN Document Server

Zhang, Guangjun

2017-01-01

This book summarizes the research advances in star identification that the author’s team has made over the past 10 years, systematically introducing the principles of star identification, general methods, key techniques and practicable algorithms. It also offers examples of hardware implementation and performance evaluation for the star identification algorithms. Star identification is the key step for celestial navigation and greatly improves the performance of star sensors, and as such the book include the fundamentals of star sensors and celestial navigation, the processing of the star catalog and star images, star identification using modified triangle algorithms, star identification using star patterns and using neural networks, rapid star tracking using star matching between adjacent frames, as well as implementation hardware and using performance tests for star identification. It is not only valuable as a reference book for star sensor designers and researchers working in pattern recognition and othe...

Symbiotic stars

Science.gov (United States)

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Nanotechnology applications and implications research supported by the US Environmental Protection Agency STAR grants program.

Science.gov (United States)

Savage, Nora; Thomas, Treye A; Duncan, Jeremiah S

2007-10-01

Since 2002, the US Environmental Protection Agency (EPA) has been funding research on the environmental aspects of nanotechnology through its Science to Achieve Results (STAR) grants program. In total, more than $25 million has been awarded for 86 research projects on the environmental applications and implications of nanotechnology. In the applications area, grantees have produced promising results in green manufacturing, remediation, sensors, and treatment using nanotechnology and nanomaterials. Although there are many potential benefits of nanotechnology, there has also been increasing concern about the environmental and health effects of nanomaterials, and there are significant gaps in the data needed to address these concerns. Research performed by STAR grantees is beginning to address these needs.

Stellar Variability at the Main-sequence Turnoff of the Intermediate-age LMC Cluster NGC 1846

Science.gov (United States)

Salinas, R.; Pajkos, M. A.; Vivas, A. K.; Strader, J.; Contreras Ramos, R.

2018-04-01

Intermediate-age (IA) star clusters in the Large Magellanic Cloud (LMC) present extended main-sequence turn-offs (MSTO) that have been attributed to either multiple stellar populations or an effect of stellar rotation. Recently it has been proposed that these extended main sequences can also be produced by ill-characterized stellar variability. Here we present Gemini-S/Gemini Multi-Object Spectrometer (GMOS) time series observations of the IA cluster NGC 1846. Using differential image analysis, we identified 73 new variable stars, with 55 of those being of the Delta Scuti type, that is, pulsating variables close the MSTO for the cluster age. Considering completeness and background contamination effects, we estimate the number of δ Sct belonging to the cluster between 40 and 60 members, although this number is based on the detection of a single δ Sct within the cluster half-light radius. This amount of variable stars at the MSTO level will not produce significant broadening of the MSTO, albeit higher-resolution imaging will be needed to rule out variable stars as a major contributor to the extended MSTO phenomenon. Though modest, this amount of δ Sct makes NGC 1846 the star cluster with the highest number of these variables ever discovered. Lastly, our results present a cautionary tale about the adequacy of shallow variability surveys in the LMC (like OGLE) to derive properties of its δ Sct population. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).

A Decade of Field Changing Atmospheric Aerosol Research: Outcomes of EPA’s STAR Program

Science.gov (United States)

Conference: Gordon Research Conference in Atmospheric Chemistry, July 28 – August 2, 2013, VermontPresentation Type: PosterTitle: An Analysis of EPA’s STAR Program and a Decade of Field Changing Research in Atmospheric AerosolsAuthors: Kristina M. Wagstrom1,2, Sherri ...

Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

2011-11-01

shells typical of luminous blue variable and late WN-type Wolf-Rayet stars.

Monitoring the High-Energy Radiation Environment of Exoplanets around Lowmass Stars with SPARCS (Star-Planet Activity Research CubeSat)

Science.gov (United States)

Shkolnik, Evgenya

Seventy-five billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1–0.4 AU). JWST will characterize HZ M dwarf planets and attempt the first spectroscopic search for life beyond the Solar System. Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The UV flux emitted during the super-luminous premain sequence phase of M stars drives water loss and photochemical O2 buildup for terrestrial planets within the HZ. This phase can persist for up to a billion years for the lowest mass M stars. Afterwards, UV-driven photochemistry during the main sequence phase strongly affects a planet’s atmosphere, could limit the planet’s potential for habitability, and may confuse studies of habitability by creating false chemical biosignatures. Our proposed CubeSat observatory will be the first mission to provide the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. These measurements are crucial to interpreting observations of planetary atmospheres around low-mass stars. Mission: The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to monitoring 25 M stars in two UV bands: SPARCS far-UV (S- FUV: 153–171 nm) and SPARCS near-UV (S-NUV: 260– 300 nm). For each target, SPARCS will observe continuously between one and three complete stellar rotations (4–45 days) over a mission lifetime of 2 years. A UV characterization survey of M dwarfs, the most common of planet hosts, is a perfect experiment for a CubeSat: - UV astronomy cannot be done from the ground because of Earth’s atmospheric absorption

Type II Cepheids: evidence for Na-O anticorrelation for BL Her type stars?

Science.gov (United States)

Kovtyukh, V.; Yegorova, I.; Andrievsky, S.; Korotin, S.; Saviane, I.; Lemasle, B.; Chekhonadskikh, F.; Belik, S.

2018-06-01

The chemical composition of 28 Population II Cepheids and one RR Lyrae variable has been studied using high-resolution spectra. The chemical composition of W Vir variable stars (with periods longer than 8 d) is typical for the halo and thick disc stars. However, the chemical composition of BL Her variables (with periods of 0.8-4 d) is drastically different, although it does not differ essentially from that of the stars belonging to globular clusters. In particular, the sodium overabundance ([Na/Fe] ≈ 0.4) is reported for most of these stars, and the Na-O anticorrelation is also possible. The evolutionary tracks for BL Her variables (with a progenitor mass value of 0.8 solar masses) indicate that mostly helium-overabundant stars (Y = 0.30-0.35) can fall into the instability strip region. We suppose that it is the helium overabundance that accounts not only for the existence of BL Her variable stars but also for the observed abnormalities in the chemical composition of this small group of pulsating variables.

SHORT- AND LONG-TERM RADIO VARIABILITY OF YOUNG STARS IN THE ORION NEBULA CLUSTER AND MOLECULAR CLOUD

International Nuclear Information System (INIS)

Rivilla, V. M.; Martín-Pintado, J.; Chandler, C. J.; Sanz-Forcada, J.; Jiménez-Serra, I.; Forbrich, J.

2015-01-01

We have used the Karl G. Jansky Very Large Array (VLA) to carry out multi-epoch radio continuum monitoring of the Orion Nebula Cluster (ONC) and the background Orion Molecular Cloud (OMC; 3 epochs at Q band and 11 epochs at Ka band). Our new observations reveal the presence of 19 radio sources, mainly concentrated in the Trapezium Cluster and the Orion Hot Core (OHC) regions. With the exception of the Becklin–Neugebauer object and source C (which we identify here as dust emission associated with a proplyd) the sources all show radio variability between the different epochs. We have found tentative evidence of variability in the emission from the massive object related to source I. Our observations also confirm radio flux density variations of a factor >2 on timescales of hours to days in five sources. One of these flaring sources, OHC-E, has been detected for the first time. We conclude that the radio emission can be attributed to two different components: (i) highly variable (flaring) non-thermal radio gyrosynchrotron emission produced by electrons accelerated in the magnetospheres of pre-main-sequence low-mass stars and (ii) thermal emission due to free–free radiation from ionized gas and/or heated dust around embedded massive objects and proplyds. Combining our sample with other radio monitoring at 8.3 GHz and the X-ray catalog provided by Chandra, we have studied the properties of the entire sample of radio/X-ray stars in the ONC/OMC region (51 sources). We have found several hints of a relation between the X-ray activity and the mechanisms responsible for (at least some fraction of) the radio emission. We have estimated a radio flaring rate of ∼0.14 flares day −1 in the dense stellar cluster embedded in the OHC region. This suggests that radio flares are more common events during the first stages of stellar evolution than previously thought. The advent of improved sensitivity with the new VLA and ALMA will dramatically increase the number of stars in

STAR: Preparing future science and math teachers through authentic research experiences at national laboratories

Science.gov (United States)

Keller, John; Rebar, Bryan

2012-11-01

The STEM Teacher and Researcher (STAR) Program provides 9-week paid summer research experiences at national research laboratories for future science and math teachers. The program, run by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the entire California State University (CSU) System, has arranged 290 research internships for 230 STEM undergraduates and credential candidates from 43 campuses over the past 6 years. The program has partnered with seven Department of Energy labs, four NASA centers, three NOAA facilities, and the National Optical Astronomy Observatory (NOAO). Primary components of the summer experience include a) conducting research with a mentor or mentor team, b) participating in weekly 2-3 hour workshops focused on translating lessons learned from summer research into classroom practice, and c) presenting a research poster or oral presentation and providing a lesson plan linked to the summer research experience. The central premise behind the STAR Program is that future science and math teachers can more effectively prepare the next generation of science, math, and engineering students if they themselves have authentic experiences as researchers.

The heterogeneity of surfaces of magnetic Ap stars

International Nuclear Information System (INIS)

Hack, M.

1977-01-01

The observations of spectrum-variability and light-variability of Ap stars are reviewed. It is shown that these variations are interpretable as due to the changing aspect of the spotted surface as the star rotates. It is stressed that the geometry of the phenomenon is understood fairly well but the physics is very far from being understood. (Auth.)

New solutions of the star-triangle relation with discrete and continuous spin variables

OpenAIRE

Kels, Andrew P.

2015-01-01

A new solution to the star-triangle relation is given, for an Ising type model that involves interacting spins, that contain integer and real valued components. Boltzmann weights of the model are given in terms of the lens elliptic-gamma function, and are based on Yamazaki's recently obtained solution of the star-star relation. The star-triangle given here, implies Seiberg duality for the $4\\!-\\!d$ $\\mathcal{N}=1$ $S_1\\times S_3/\\mathbb{Z}_r$ index of the $SU(2)$ quiver gauge theory, and the ...

Low-Frequency Temporal Variability in Mira and Semiregular Variables

Science.gov (United States)

Templeton, Matthew R.; Karovska, M.; Waagen, E. O.

2012-01-01

We investigate low-frequency variability in a large sample of Mira and semiregular variables with long-term visual light curves from the AAVSO International Database. Our aim is to determine whether we can detect and measure long-timescale variable phenomena in these stars, for example photometric variations that might be associated with supergranular convection. We analyzed the long-term light curves of 522 variable stars of the Mira and SRa, b, c, and d classes. We calculated their low-frequency time-series spectra to characterize rednoise with the power density spectrum index, and then correlate this index with other observable characteristics such as spectral type and primary pulsation period. In our initial analysis of the sample, we see that the semiregular variables have a much broader range of spectral index than the Mira types, with the SRb subtype having the broadest range. Among Mira variables we see that the M- and S-type Miras have similarly wide ranges of index, while the C-types have the narrowest with generally shallower slopes. There is also a trend of steeper slope with larger amplitude, but at a given amplitude, a wide range of slopes are seen. The ultimate goal of the project is to identify stars with strong intrinsic red noise components as possible targets for resolved surface imaging with interferometry.

SPB stars in the open SMC cluster NGC 371

Science.gov (United States)

Karoff, C.; Arentoft, T.; Glowienka, L.; Coutures, C.; Nielsen, T. B.; Dogan, G.; Grundahl, F.; Kjeldsen, H.

2008-05-01

Pulsation in β Cep and slowly pulsating B (SPB) stars are driven by the κ mechanism which depends critically on the metallicity. It has therefore been suggested that β Cep and SPB stars should be rare in the Magellanic Clouds which have lower metallicities than the solar neighbourhood. To test this prediction we have observed the open Small Magellanic Cloud (SMC) cluster NGC 371 for 12 nights in order to search for β Cep and SPB stars. Surprisingly, we find 29 short-period B-type variables in the upper part of the main sequence, many of which are probably SPB stars. This result indicates that pulsation is still driven by the κ mechanism even in low-metallicity environments. All the identified variables have periods longer than the fundamental radial period which means that they cannot be β Cep stars. Within an amplitude detection limit of 5 mmag no stars in the top of the Hertzsprung-Russell diagram show variability with periods shorter than the fundamental radial period. So if β Cep stars are present in the cluster they oscillate with amplitudes below 5 mmag, which is significantly lower than the mean amplitude of β Cep stars in the Galaxy. We see evidence that multimode pulsation is more common in the upper part of the main sequence than in the lower. We have also identified five eclipsing binaries and three periodic pulsating Be stars in the cluster field.

A HIGH-PRECISION NEAR-INFRARED SURVEY FOR RADIAL VELOCITY VARIABLE LOW-MASS STARS USING CSHELL AND A METHANE GAS CELL

Energy Technology Data Exchange (ETDEWEB)

Gagné, Jonathan [Carnegie Institution of Washington DTM, 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Plavchan, Peter [Department of Physics, Missouri State University, 901 S National Ave, Springfield, MO 65897 (United States); Gao, Peter [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Anglada-Escude, Guillem [School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Rd, E1 4NS, London (United Kingdom); Furlan, Elise; Brinkworth, Carolyn; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, 770 S. Wilson Ave., Pasadena, CA 91125 (United States); Davison, Cassy; Henry, Todd J.; White, Russel [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Tanner, Angelle [Mississippi State University, Department of Physics and Astronomy, Hilbun Hall, Starkville, MS 39762 (United States); Riedel, Adric R. [Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Latham, David; Johnson, John A. [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Bottom, Michael [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Mills, Sean [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637 (United States); Beichman, Chas [NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA 91125 (United States); Wallace, Kent; Mennesson, Bertrand [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91125 (United States); Von Braun, Kaspar, E-mail: jgagne@carnegiescience.edu [Lowell Observatory, West Mars Hill Road, Flagstaff, AZ 86001 (United States); and others

2016-05-01

We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2–M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25–150 Myr) moving groups, the young field star ε Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8–15 m s{sup −1}with a long-term stability of 15–50 m s{sup −1} over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25–50 m s{sup −1} at ≈2.3125 μ m, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3 σ –5 σ . Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s{sup −1} in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.

Machine learning search for variable stars

Science.gov (United States)

Pashchenko, Ilya N.; Sokolovsky, Kirill V.; Gavras, Panagiotis

2018-04-01

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. Logistic Regression (LR), Support Vector Machines (SVM), k Nearest Neighbours (kNN), Neural Nets (NN), Random Forests (RF), and Stochastic Gradient Boosting classifier (SGB) are applied to 18 features (variability indices) quantifying scatter and/or correlation between points in a light curve. We use a subset of Optical Gravitational Lensing Experiment phase two (OGLE-II) Large Magellanic Cloud (LMC) photometry (30 265 light curves) that was searched for variability using traditional methods (168 known variable objects) as the training set and then apply the NN to a new test set of 31 798 OGLE-II LMC light curves. Among 205 candidates selected in the test set, 178 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. The NN, SGB, SVM, and RF show a higher efficiency compared to LR and kNN.

Radio stars

International Nuclear Information System (INIS)

Hjellming, R.M.; Gibson, D.M.

1985-01-01

Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

Symbiotic stars as an old disk population

Energy Technology Data Exchange (ETDEWEB)

Wallerstein, G [Joint Inst. for Lab. Astrophysics, Boulder, CO (USA)

1981-10-01

A table of all symbiotic stars in the General Catalogue of Variable Stars and its supplements has been assembled and their radial velocities have been discussed. A velocity dispersion of 63 +- 14 km/s is found for all the stars and a value of 58 +- 14 km/s is established if the probable halo star, AG Dra, is omitted. The space distribution is similar to that of an old disk population. Some implications of low masses for the symbiotic stars are discussed, and some suggestions are made regarding possibly useful observations.

The evolutionary status of symbiotic stars

International Nuclear Information System (INIS)

Rudak, B.

1982-01-01

The evolutionary relations between symbiotic stars and cataclysmic variables are presented. The symbiotic stars are assumed to be long period detached binaries containing a carbon-oxygen degenerate primary and a red giant losing its mass through a spherically symmetric wind. Such systems can be obtained in Case C evolution, provided a common envelope during a rapid mass transfer phase was not formed. The same way recurrent novae containing a red giant as a secondary component may be produced. The factors influencing the differences between symbiotic stars and nova-type stars are discussed. (Auth.)

Time-dependent Models of Magnetospheric Accretion onto Young Stars

Energy Technology Data Exchange (ETDEWEB)

Robinson, C. E.; Espaillat, C. C. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Owen, J. E. [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States); Adams, F. C., E-mail: connorr@bu.edu [Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States)

2017-04-01

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that if the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.

Time-dependent Models of Magnetospheric Accretion onto Young Stars

International Nuclear Information System (INIS)

Robinson, C. E.; Espaillat, C. C.; Owen, J. E.; Adams, F. C.

2017-01-01

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that if the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.

Exploring M33 Through RR Lyrae Stars

OpenAIRE

Pritzl, Barton J.

2013-01-01

Recent surveys have detected RR Lyrae stars in M33, the Triangulum Galaxy. These variable stars are excellent tracers of ancient stellar populations. The RR Lyrae stars have been used to estimate metallicities at various locations within M33, as well as determining the distance to the galaxy. A summary of the M33 RR Lyrae stars is presented here as well as an analysis on what their properties imply for the unique M33 galaxy

Long-term Variability of H2CO Masers in Star-forming Regions

Science.gov (United States)

Andreev, N.; Araya, E. D.; Hoffman, I. M.; Hofner, P.; Kurtz, S.; Linz, H.; Olmi, L.; Lorran-Costa, I.

2017-10-01

We present results of a multi-epoch monitoring program on variability of 6 cm formaldehyde (H2CO) masers in the massive star-forming region NGC 7538 IRS 1 from 2008 to 2015, conducted with the Green Bank Telescope, the Westerbork Radio Telescope , and the Very Large Array. We found that the similar variability behaviors of the two formaldehyde maser velocity components in NGC 7538 IRS 1 (which was pointed out by Araya and collaborators in 2007) have continued. The possibility that the variability is caused by changes in the maser amplification path in regions with similar morphology and kinematics is discussed. We also observed 12.2 GHz methanol and 22.2 GHz water masers toward NGC 7538 IRS 1. The brightest maser components of CH3OH and H2O species show a decrease in flux density as a function of time. The brightest H2CO maser component also shows a decrease in flux density and has a similar LSR velocity to the brightest H2O and 12.2 GHz CH3OH masers. The line parameters of radio recombination lines and the 20.17 and 20.97 GHz CH3OH transitions in NGC 7538 IRS 1 are also reported. In addition, we observed five other 6 cm formaldehyde maser regions. We found no evidence of significant variability of the 6 cm masers in these regions with respect to previous observations, the only possible exception being the maser in G29.96-0.02. All six sources were also observed in the {{{H}}}213{CO} isotopologue transition of the 6 cm H2CO line; {{{H}}}213{CO} absorption was detected in five of the sources. Estimated column density ratios [{{{H}}}212{CO}]/[{{{H}}}213{CO}] are reported.

Long-period variables in the Magellanic Clouds: Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium

International Nuclear Information System (INIS)

Wood, P.; Bessell, M.S.; Fox, M.W.

1983-01-01

Infrared JHK magnitudes and low-dispersion red spectra have been obtained for 90 long-period variables (LPVs) in the Small and Large Magellanic Clouds. The LPVs fall into two distinct groups, core helium (or carbon) burning supergiants and stars on the asymptotic giant branch (AGB). The supergiants have small pulsation amplitudes in K ( or approx. =5 M/sub sun/ produce supernovae while less massive stars produce planetary nebulae with nebula masses from approx.0.1--2.1 M/sub sun/. The coreburning red supergiants appear highly overluminous for their pulsation mass, indicating that they have lost up to half their mass since the main-sequence phase

Self-assembly of star micelle into vesicle in solvents of variable quality: the star micelle retains its core-shell nanostructure in the vesicle.

Science.gov (United States)

Liu, Nijuan; He, Qun; Bu, Weifeng

2015-03-03

Intra- and intermolecular interactions of star polymers in dilute solutions are of fundamental importance for both theoretical interest and hierarchical self-assembly into functional nanostructures. Here, star micelles with a polystyrene corona and a small ionic core bearing platinum(II) complexes have been regarded as a model of star polymers to mimic their intra- and interstar interactions and self-assembled behaviors in solvents of weakening quality. In the chloroform/methanol mixture solvents, the star micelles can self-assemble to form vesicles, in which the star micelles shrink significantly and are homogeneously distributed on the vesicle surface. Unlike the morphological evolution of conventional amphiphiles from micellar to vesicular, during which the amphiphilic molecules are commonly reorganized, the star micelles still retain their core-shell nanostructures in the vesicles and the coronal chains of the star micelle between the ionic cores are fully interpenetrated.

VLA observations of dwarf M flare stars and magnetic stars

Science.gov (United States)

Willson, R. F.; Lang, K. R.; Foster, P.

1988-01-01

The VLA has been used to search for 6 cm emission from 16 nearby dwarf M stars, leading to the detection of only one of them - Gliese 735. The dwarf M flare stars AD Leonis and YZ Canis Minoris were also monitored at 6 cm and 20 cm wavelength in order to study variability. Successive oppositely circularly polarized bursts were detected from AD Leo at 6 cm, suggesting the presence of magnetic fields of both magnetic polarities. An impulsive 20-cm burst from YZ CMi preceded slowly varying 6-cm emission. The VLA was also used, unsuccessfully, to search for 6-cm emission from 13 magnetic Ap stars, all of which exhibit kG magnetic fields. Although the Ap magnetic stars have strong dipolar magnetic fields, the failure to detect gyroresonant radiation suggests that these stars do not have hot, dense coronae. The quiescent microwave emission from GL 735 is probably due to nonthermal radiation, since unusually high (H = 50 kG or greater) surface magnetic fields are inferred under the assumption that the 6-cm radiation is the gyroresonant radiation of thermal electrons.

A radial velocity survey of extremely hydrogen-deficient stars

International Nuclear Information System (INIS)

Jeffery, C.S.; Kiel Univ.; Drilling, J.S.; Heber, U.

1987-01-01

A radial velocity survey of hot extremely hydrogen-deficient stars has been carried out in order to search for possible binaries. The survey found three stars to have large velocity variations. Of these, two are known hydrogen-deficient binaries and one, HDE 320156 (= LSS 4300), is a suspected binary. HDE 320156 (= LSS 4300) is therefore confirmed to be a single-lined spectroscopic hydrogen-deficient binary. The hydrogen-deficient binary stars all show weak C-lines. The remaining stars in the sample are C-strong extreme-helium (EHe) stars and did not show large-amplitude velocity variations. Small-amplitude radial velocity variations known to be present amongst the EHe stars are largely undetected. Evidence for variability is, however, present in the known variable V2076 Oph (HD 160641) and in LS IV - 1 0 2 with amplitudes between 10 and 20 km s -1 . (author)

Star Polymers.

Science.gov (United States)

Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

2016-06-22

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

NEAR-INFRARED VARIABILITY AMONG YOUNG STELLAR OBJECTS IN THE STAR FORMATION REGION CYGNUS OB7

Energy Technology Data Exchange (ETDEWEB)

Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

2013-08-20

We present an analysis of near-infrared time-series photometry in J, H, and K bands for about 100 epochs of a 1 Degree-Sign Multiplication-Sign 1 Degree-Sign region of the Lynds 1003/1004 dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field Infrared Survey Explorer, we identify 96 candidate disk bearing young stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or earlier. Using the Wide-Field Imaging Camera on the United Kingdom Infrared Telescope, we were able to obtain photometry over three observing seasons, with photometric uncertainty better than 0.05 mag down to J Almost-Equal-To 17. We study detailed light curves and color trajectories of {approx}50 of the YSOs in the monitored field. We investigate the variability and periodicity of the YSOs and find the data are consistent with all YSOs being variable in these wavelengths on timescales of a few years. We divide the variability into four observational classes: (1) stars with periodic variability stable over long timescales, (2) variables which exhibit short-lived cyclic behavior, (3) long-duration variables, and (4) stochastic variables. Some YSO variability defies simple classification. We can explain much of the observed variability as being due to dynamic and rotational changes in the disk, including an asymmetric or changing blocking fraction, changes to the inner disk hole size, as well as changes to the accretion rate. Overall, we find that the Class I:Class II ratio of the cluster is consistent with an age of <1 Myr, with at least one individual, wildly varying source {approx}100, 000 yr old. We have also discovered a Class II eclipsing binary system with a period of 17.87 days.

Colour relations for Mira and Semiregular (SR) type stars

International Nuclear Information System (INIS)

Guney, Yavuz; Yesilyaprak, Cahit

2016-01-01

In this study, the period-colour relations, the colour-colour relations and the effective temperature were examined for Semiregular (SR) and Mira type variable stars. SR variables show an obvious period-colour relations, especially in infrared (IR). There are differences between SR and Mira type variable stars with respect to their colour relations. It has been thought that these differencies are caused by their mass loss rates and their effective temperatures. (paper)

Shock Thermodynamic Applied Research Facility (STAR)

Data.gov (United States)

Federal Laboratory Consortium — The STAR facility, within Sandia's Solid Dynamic Physics Department, is one of a few institutions in the world with a major shock-physics program. This is the only...

SX Phoenicis stars

International Nuclear Information System (INIS)

Nemec, J.; Mateo, M.

1990-01-01

The purpose of this paper is to review the basic observational information concerning SX Phe stars, including recent findings such as the discovery of about 40 low-luminosity variable stars in the Carina dwarf galaxy and identification of at least one SX Phe star in the metal-rich globular cluster M71. Direct evidence supporting the hypothesis that at least some BSs are binary systems comes from the discovery of two contact binaries and a semidetached binary among the 50 BSs in the globular cluster NGC 5466. Since these systems will coalesce on a time scale 500 Myr, it stands to reason that many (if not most) BSs are coalesced binaries. The merger hypothesis also explains the relatively-large masses (1.0-1.2 solar masses) that have been derived for SX Phe stars and halo BSs, and may also account for the nonvariable BSs in the 'SX Phe instability strip'. 132 refs

The Training Project of Star Researchers, Outstanding Teaching Staff and Leaders with Facilities Available

Directory of Open Access Journals (Sweden)

Ömer KARAHAN

2015-12-01

Full Text Available There is a general consensus on the requirement of a serious regulation at our universities. It is argued that it is necessary to change Constitution and Institution of Higher Education Law for the serious regulation. However, it is impossible to say that all the facilities of the present legislation are used. Our aim is to create a project based on benefiting from continuing education centers to meet the need of star researchers, outstanding teaching staff and leaders in Turkey via the legislation in force. In this study, accessible studies from publications related to university, higher education and continuing education centers are studied. Th e current situation and solution off ers, applications and continuing education centers'activities have been determined. In accordance with these data, solution off ers have been proposed and discussed in line with the literature. According to the data obtained, our students who come with deficiencies from high schools to universities are not given the adequate undergraduate, graduate and postgraduate education. Th ere are studies such as ‘Double Major Program', ‘Medical-Science Physicians Integrated (MD-PhD Doctorate Program which upgrade the qualities. However, these programs are not suff icient and common. Th erefore, it is imposssible to train outstanding teaching staff , star researchesr and leaders who will meet the needs of our country and contribute to the World. Our academic potential needs a quality training except for branch training. On the other hand, the contribution of the Continuing Education Centers existing in university embodiments is limited. It is possible to provide basic skills, integration and research education to the outstanding teaching staff , star researcher and leader candidates. Th ese trainings should be given in a continuous instutionalization and in the formal education system. For this purpose, an academician school can be established within the body continuing

Collective Variables in Apphed Linguistics Research

OpenAIRE

ヘンスリー, ジョール; HENSLEY, Joel

2011-01-01

This paper focuses on the key dynamic(al)systems theory concept of collective variables as it relates to developmental research in applied linguistics. Dynamic(al) systems theory is becoming prevalent in linguistic research and in the past two decades has jumped to the forefront of cutting edge in the field. One key concept in dynamic(al) systems theory is that of collective variables. In order to help properly orient this concept in the field of applied linguistics, this paper discusses the ...

News and Views: Kleopatra a pile of rubble, shedding moons; Did plasma flow falter to stretch solar minimum? Amateurs hit 20 million variable-star observations; Climate maths; Planetary priorities; New roles in BGA

Science.gov (United States)

2011-04-01

Metallic asteroid 216 Kleopatra is shaped like a dog's bone and has two tiny moons - which came from the asteroid itself - according to a team of astronomers from France and the US, who also measured its surprisingly low density and concluded that it is a collection of rubble. The recent solar minimum was longer and lower than expected, with a low polar field and an unusually large number of days with no sunspots visible. Models of the magnetic field and plasma flow within the Sun suggest that fast, then slow meridional flow could account for this pattern. Variable stars are a significant scientific target for amateur astronomers. The American Association of Variable Star Observers runs the world's largest database of variable star observations, from volunteers, and reached 20 million observations in February.

Pulsating stars in SuperWASP

Directory of Open Access Journals (Sweden)

Holdsworth Daniel L.

2017-01-01

Full Text Available SuperWASP is one of the largest ground-based surveys for transiting exoplanets. To date, it has observed over 31 million stars. Such an extensive database of time resolved photometry holds the potential for extensive searches of stellar variability, and provide solid candidates for the upcoming TESS mission. Previous work by e.g. [15], [5], [12] has shown that the WASP archive provides a wealth of pulsationally variable stars. In this talk I will provide an overview of the SuperWASP project, present some of the published results from the survey, and some of the on-going work to identify key targets for the TESS mission.

Identification of Cepheid Variables in ASAS Data (Poster abstract)

Science.gov (United States)

Johnson, J.; Larsen, K.

2014-06-01

(Abstract only) Cepheid variables are well-known to be important to astronomers, as their period-luminosity relationship is used to determine the distances to galaxies. The unambiguous identification of newly discovered Cepheid variables in large photometric data sets is therefore of significance. A data set of 3,548 candidate Cepheid variable stars in the ASAS data was provided by Patrick Wils (through Doug Welch). A computer program had originally identified these candidates; however, Wils investigated a small subset of the data by hand and discovered that the vast majority of these stars were misidentified. The most common misidentification was of BY Draconis stars (rotating spotted K and M dwarfs). In a companion piece, Swenton and Larsen sought out the most likely Cepheid candidates in the data; the work discussed here is instead focused on looking at stars that had properties that were clearly different from Cepheids, more specifically properties likely to be seen in BY Dra stars. We are sorting the spreadsheet stars by characteristics in order to find as many BY Dra variables as possible (since they seem to be the most commonly misidentified stars). These characteristics include newly available infrared photometry (2MASS), proper motion (PPMXL), and X-Ray emission (ROTSE) data (for which we received helpful guidance from Sebastian Otero) as well as VSX information. The first 103 stars to be studied are those with the smallest range in magnitude (less than or equal to 0.1). An analysis of their light curves and other available data is being undertaken in order to determine whether or not they are indeed BY Dra-type variables. In doing so the goal is to be able to submit and publish the correct identifications for these stars to the International Variable Star Index (VSX) and the JAAVSO.

Similar star formation rate and metallicity variability time-scales drive the fundamental metallicity relation

Science.gov (United States)

Torrey, Paul; Vogelsberger, Mark; Hernquist, Lars; McKinnon, Ryan; Marinacci, Federico; Simcoe, Robert A.; Springel, Volker; Pillepich, Annalisa; Naiman, Jill; Pakmor, Rüdiger; Weinberger, Rainer; Nelson, Dylan; Genel, Shy

2018-06-01

The fundamental metallicity relation (FMR) is a postulated correlation between galaxy stellar mass, star formation rate (SFR), and gas-phase metallicity. At its core, this relation posits that offsets from the mass-metallicity relation (MZR) at a fixed stellar mass are correlated with galactic SFR. In this Letter, we use hydrodynamical simulations to quantify the time-scales over which populations of galaxies oscillate about the average SFR and metallicity values at fixed stellar mass. We find that Illustris and IllustrisTNG predict that galaxy offsets from the star formation main sequence and MZR oscillate over similar time-scales, are often anticorrelated in their evolution, evolve with the halo dynamical time, and produce a pronounced FMR. Our models indicate that galaxies oscillate about equilibrium SFR and metallicity values - set by the galaxy's stellar mass - and that SFR and metallicity offsets evolve in an anticorrelated fashion. This anticorrelated variability of the metallicity and SFR offsets drives the existence of the FMR in our models. In contrast to Illustris and IllustrisTNG, we speculate that the SFR and metallicity evolution tracks may become decoupled in galaxy formation models dominated by feedback-driven globally bursty SFR histories, which could weaken the FMR residual correlation strength. This opens the possibility of discriminating between bursty and non-bursty feedback models based on the strength and persistence of the FMR - especially at high redshift.

Cataclysmic variables, Hubble-Sandage variables and eta Carinae

International Nuclear Information System (INIS)

Bath, G.T.

1980-01-01

The Hubble-Sandage variables are the most luminous stars in external galaxies. They were first investigated by Hubble and Sandage (1953) for use as distance indicators. Their main characteristics are high luminosity, blue colour indices, and irregular variability. Spectroscopically they show hydrogen and helium in emission with occasionally weaker FeII and [FeII], and no Balmer jump (Humphreys 1975, 1978). In this respect they closely resemble cataclysmic variables, particularly dwarf novae. In the quiescent state dwarf novae show broad H and HeI, together with a strong UV continuum. In contrast to the spectroscopic similarities, the luminosities could hardly differ more. Rather than being the brightest stars known, quiescent dwarf novae are as faint or fainter than the sun. It is suggested that the close correspondence between the spectral appearance of the two classes combined with the difference in luminosity is well accounted for by a model of Hubble-Sandage variables in which the same physical processes are occurring, but on a larger scale. (Auth.)

Collaborative Research of Open Star Clusters Alisher S. Hojaev

Indian Academy of Sciences (India)

Some spectra of the young star candidates with dispersion 50 and 200 Å/mm were .... Color-magnitude diagram for o band and o band minus i band for stars in the region of NGC ... Statistical analysis for open cluster parameters investigation.

Period Changes of 23 Field RR Lyrae Stars

Directory of Open Access Journals (Sweden)

Soo-Chang Rey

1994-12-01

Full Text Available The secular period behavior of 23 field RR Lyrae stars is studied in order to determine if the observed period changes could be attributed, at least in the mean, to stellar evolution. The sample of stars is subdivided into two Oosterhoff groups based on the metallicity and period-shift. Despite the small sample size, we found a distinct bias toward positive period changes in the group variables. The period changes of the group variables in globular clusters. This provides yet another support for the Lee, Demarque, and Zinn(1990 evolutionary models of RR Lyrae stars and their explanation of the Sandage period-shift effect.

AGB stellar evolution and symbiotic stars

International Nuclear Information System (INIS)

Schild, H.

1989-01-01

Published data on the mass loss rates and periods of Miras and OH/IR stars have been compiled. There is a good correlation between mass loss rate and period and a smooth transition from Miras to OH/IR sources. At periods below 600 d. the mass loss increases exponentially but at longer periods it remains constant. As a Mira evolves from short to longer periods, its mass loss rate increases dramatically. Phenomenologically, the object evolves from a classical Mira into a variable OH/IR source. Symbiotic stars cluster in the transition zone where Miras transform into OH/IR stars and mass loss increase is at its steepest. The red star in these symbiotic systems is in the same evolutionary status as short periodic OH/IR stars. (author)

A-type central stars of planetary nebulae. 2. The central stars of NGC 2346, He 2-36 and NGC 3132

Energy Technology Data Exchange (ETDEWEB)

Mendez, R H [Instituto de Astronomia y Fisica del Espacio, Buenos Aires (Argentina)

1978-12-01

Spectrograms, scanner, uvby and ANS ultraviolet measurements of the central stars of NGC 2346, He 2-36 and NGC 3132 are analysed. The observations suggest that the first one is a foreground horizontal-branch star, and the second is above the horizontal branch, presumably in a rapid evolutionary phase. Both objects are probably variable. The central star of NGC 3132 is a slightly evolved main-sequence star with a hot visual companion. The evolutionary status of this system is briefly discussed.

ultra-Stable Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (5STAR)

Science.gov (United States)

Dunagan, S. E.; Johnson, R. R.; Redemann, J.; Holben, B. N.; Schmid, B.; Flynn, C. J.; Fahey, L.; LeBlanc, S. E.; Liss, J.; Kacenelenbogen, M. S.; Segal-Rosenhaimer, M.; Shinozuka, Y.; Dahlgren, R. P.; Pistone, K.; Karol, Y.

2017-12-01

The Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) combines airborne sun tracking and sky scanning with diffraction spectroscopy to improve knowledge of atmospheric constituents and their links to air pollution and climate. Direct beam hyperspectral measurement of optical depth improves retrievals of gas constituents and determination of aerosol properties. Sky scanning enhances retrievals of aerosol type and size distribution. Hyperspectral cloud-transmitted radiance measurements enable the retrieval of cloud properties from below clouds. These measurements tighten the closure between satellite and ground-based measurements. 4STAR incorporates a modular sun-tracking/ sky-scanning optical head with optical fiber signal transmission to rack mounted spectrometers, permitting miniaturization of the external optical tracking head, and future detector evolution. 4STAR has supported a broad range of flight experiments since it was first flown in 2010. This experience provides the basis for a series of improvements directed toward reducing measurement uncertainty and calibration complexity, and expanding future measurement capabilities, to be incorporated into a new 5STAR instrument. A 9-channel photodiode radiometer with AERONET-matched bandpass filters will be incorporated to improve calibration stability. A wide dynamic range tracking camera will provide a high precision solar position tracking signal as well as an image of sky conditions around the solar axis. An ultrasonic window cleaning system design will be tested. A UV spectrometer tailored for formaldehyde and SO2 gas retrievals will be added to the spectrometer enclosure. Finally, expansion capability for a 4 channel polarized radiometer to measure the Stokes polarization vector of sky light will be incorporated. This paper presents initial progress on this next-generation 5STAR instrument. Keywords: atmosphere; climate; pollution; radiometry; technology; hyperspectral; fiber optic

Interrogation of duplicitous stars with an APT

Science.gov (United States)

Bopp, Bernard W.

1992-01-01

Preliminary results from intensive spectroscopic and APT monitoring of two interacting binary systems are presented. Both V644 Mon (Be + K:) and HD 37453 (F5 II + B) show complex, composite, and variable spectral. APT observations extending over three years show both stars to vary by 0.1-0.2 mag in V. The photometric variability of V644 Mon appears to be irregular, though there is some evidence for periodic behavior in the 50-60 day range. HD 37453 has an orbital period of 66.75 days; the best-fit photometric period is not quite half this value, indicating the star is an ellipsoidal variable.

Post-giant evolution of helium stars

International Nuclear Information System (INIS)

Schoenberner, D.

1977-01-01

Extremely hydrogen deficient stars (helium stars and R Coronae Borealis variables) are considered to be remnants of double shell source stars (of the asymptotic giant branch). The evolution of stars with a condensed C/O-core and a helium envelope is followed numerically from the red giant stage to the white dwarf domain, crossing the regions of R CrB- and helium stars (so far analyzed). They have typically masses M/M(sun) = 0.7 and luminosities log L/L(sun) = 4.1. The time for crossing the helium star domain is some 10 3 years. The corresponding times in the R CrB-region amounts up to several 10 4 years. The lower limit of the death rate of helium stars is estimated to be 4 x 10 -14 pc -3 yr -1 . This value is only a factor of ten lower than the birth rate of all non-DA white dwarfs. It is therefore possible that the helium stars are the precursors of helium rich white dwarfs. As a consequence, a significant fraction of all stars which end their lives as white dwarfs should pass through the helium star phase. (orig.) [de

Two-color photographic photometry of variables in the globular cluster M28

International Nuclear Information System (INIS)

Wehlau, A.; Butterworth, S.

1990-01-01

Visual magnitudes have been measured for 20 variables on 32 plates of M28. These have been combined with previously published as well as newly determined blue magnitudes in order to obtain colors for the variables. Blue and visual light curves are presented for 15 of the the variables, including one W Virginis star V4, one RV Tauri star V17, one field Mira variable V7, nine cluster RR Lyrae stars, and three field RR Lyrae stars. It is shown that V14, previously thought to be a c type RR Lyrae star, is to the red of the instability strip. The visual light curve of V9 suggests that the star may be a member of a binary or a very close optical double. Possible evidence for differential reddening in the vicinity of M28 is presented. The bimodal distribution of the periods of the RR Lyrae stars in M28 may indicate a spread in metallicity among the RR Lyrae variables. 16 refs

Heartbeat stars and the ringing of tidal pulsations

OpenAIRE

García, RA; Hambleton, K; Kurtz, DW; Prsa, A; Fuller, J; Thompson (SU), S; Ballot, J

2015-01-01

With the advent of high precision photometry from satellites such as Kepler and CoRoT, a whole new layer of interesting and astounding astronomical objects has been revealed: heartbeat stars are an example of such objects. Heartbeat stars are eccen- tric ellipsoidal variables that undergo strong tidal interactions when the stars are almost in contact at the time of closest approach. These interactions deform of the stars and cause a notable light curve variation in the form of a tidal pulse. ...

MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

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Lii Patrick

2014-01-01

Full Text Available Accreting magnetized stars may be in the propeller regime of disc accretion in which the angular velocity of the stellar magnetosphere exceeds that of the inner disc. In these systems, the stellar magnetosphere acts as a centrifugal barrier and inhibits matter accretion onto the rapidly rotating star. Instead, the matter accreting through the disc accumulates at the disc-magnetosphere interface where it picks up angular momentum and is ejected from the system as a wide-angled outflow which gradually collimates at larger distances from the star. If the ejection rate is lower than the accretion rate, the matter will accumulate at the boundary faster than it can be ejected; in this case, accretion onto the star proceeds through an episodic accretion instability in which the episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion of matter onto the star. In addition to the matter dominated wind component, the propeller outflow also exhibits a well-collimated, magnetically-dominated Poynting jet which transports energy and angular momentum away from the star. The propeller mechanism may explain some of the weakly-collimated jets and winds observed around some T Tauri stars as well as the episodic variability present in their light curves. It may also explain some of the quasi-periodic variability observed in cataclysmic variables, millisecond pulsars and other magnetized stars.

Monitoring pulsating giant stars in M33: star formation history and chemical enrichment

Science.gov (United States)

Javadi, A.; van Loon, J. Th

2017-06-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified. We give evidence of two epochs of a star formation rate enhanced by a factor of a few. These stars are also important dust factories, we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. Then the monitoring survey was expanded to cover a much larger part of M33 including spiral arms. Here we present our methodology and describe results for the central square kiloparsec of M33 [1-4] and disc of M33 [5-8].

Monitoring pulsating giant stars in M33: star formation history and chemical enrichment

International Nuclear Information System (INIS)

Javadi, A; Van Loon, J Th

2017-01-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). A new method has been developed by us to use pulsating giant stars to reconstruct the star formation history of galaxies over cosmological time as well as using them to map the dust production across their host galaxies. In first Instance the central square kiloparsec of M33 was monitored and long period variable stars (LPVs) were identified. We give evidence of two epochs of a star formation rate enhanced by a factor of a few. These stars are also important dust factories, we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. Then the monitoring survey was expanded to cover a much larger part of M33 including spiral arms. Here we present our methodology and describe results for the central square kiloparsec of M33 [1–4] and disc of M33 [5–8]. (paper)

On the phase form of a deformation quantization with separation of variables

Science.gov (United States)

Karabegov, Alexander

2016-06-01

Given a star product with separation of variables on a pseudo-Kähler manifold, we obtain a new formal (1, 1)-form from its classifying form and call it the phase form of the star product. The cohomology class of a star product with separation of variables equals the class of its phase form. We show that the phase forms can be arbitrary and they bijectively parametrize the star products with separation of variables. We also describe the action of a change of the formal parameter on a star product with separation of variables, its formal Berezin transform, classifying form, phase form, and canonical trace density.

Physics of neutron star interiors

International Nuclear Information System (INIS)

Blaschke, D.

2001-01-01

Neutron stars are the densest observable bodies in our universe. Born during the gravitational collapse of luminous stars - a birth heralded by spectacular supernova explosions - they open a window on a world where the state of the matter and the strength of the fields are anything but ordinary. This book is a collection of pedagogical lectures on the theory of neutron stars, and especially their interiors, at the forefront of current research. It adresses graduate students and researchers alike, and should be particularly suitable as a text bridging the gap between standard textbook material and the research literature

Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

Science.gov (United States)

Zong, Weikai; Charpinet, Stéphane; Fu, Jian-Ning; Vauclair, Gérard; Niu, Jia-Shu; Su, Jie

2018-02-01

We present the first results of an ensemble and systematic survey of oscillation mode variability in pulsating hot B subdwarf (sdB) and white dwarf stars observed with the original Kepler mission. The satellite provides uninterrupted high-quality photometric data with a time baseline that can reach up to 4 yr collected on pulsating stars. This is a unique opportunity to characterize long-term behaviors of oscillation modes. A mode modulation in amplitude and frequency can be independently inferred by its fine structure in the Fourier spectrum, from the sLSP, or with prewhitening methods applied to various parts of the light curve. We apply all these techniques to the sdB star KIC 3527751, a long-period-dominated hybrid pulsator. We find that all the detected modes with sufficiently large amplitudes to be thoroughly studied show amplitude and/or frequency variations. Components of three identified quintuplets around 92, 114, and 253 μHz show signatures that can be linked to nonlinear interactions according to the resonant mode coupling theory. This interpretation is further supported by the fact that many oscillation modes are found to have amplitudes and frequencies showing correlated or anticorrelated variations, a behavior that can be linked to the amplitude equation formalism, where nonlinear frequency corrections are determined by their amplitude variations. Our results suggest that oscillation modes varying with diverse patterns are a very common phenomenon in pulsating sdB stars. Close structures around main frequencies therefore need to be carefully interpreted in light of this finding to secure a robust identification of real eigenfrequencies, which is crucial for seismic modeling. The various modulation patterns uncovered should encourage further developments in the field of nonlinear stellar oscillation theory. It also raises a warning to any long-term project aiming at measuring the rate of period change of pulsations caused by stellar evolution, or at

Spectrum variability of the silicon Ap star HD 192913

International Nuclear Information System (INIS)

Riabchikova, T.A.; Davidova, E.S.; Adelman, S.J.

1990-01-01

The metal lines in the spectrum of the silicon Ap star HD 192913 are found to change with the photometric period. Many commonly found atomic species have lines which vary together in phase. The spectrum contains lines of most of the doubly ionized rare earth elements. 27 refs

On the phase form of a deformation quantization with separation of variables

OpenAIRE

Karabegov, Alexander

2015-01-01

Given a star product with separation of variables on a pseudo-Kaehler manifold, we obtain a new formal (1,1)-form from its classifying form and call it the phase form of the star product. The cohomology class of a star product with separation of variables equals the class of its phase form. We show that the phase forms can be arbitrary and they bijectively parametrize the star products with separation of variables. We also describe the action of a change of the formal parameter on a star prod...

STAR facility tritium accountancy

International Nuclear Information System (INIS)

Pawelko, R. J.; Sharpe, J. P.; Denny, B. J.

2008-01-01

The Safety and Tritium Applied Research (STAR) facility has been established to provide a laboratory infrastructure for the fusion community to study tritium science associated with the development of safe fusion energy and other technologies. STAR is a radiological facility with an administrative total tritium inventory limit of 1.5 g (14,429 Ci) [1]. Research studies with moderate tritium quantities and various radionuclides are performed in STAR. Successful operation of the STAR facility requires the ability to receive, inventory, store, dispense tritium to experiments, and to dispose of tritiated waste while accurately monitoring the tritium inventory in the facility. This paper describes tritium accountancy in the STAR facility. A primary accountancy instrument is the tritium Storage and Assay System (SAS): a system designed to receive, assay, store, and dispense tritium to experiments. Presented are the methods used to calibrate and operate the SAS. Accountancy processes utilizing the Tritium Cleanup System (TCS), and the Stack Tritium Monitoring System (STMS) are also discussed. Also presented are the equations used to quantify the amount of tritium being received into the facility, transferred to experiments, and removed from the facility. Finally, the STAR tritium accountability database is discussed. (authors)

Analysis of a selected sample of RR Lyrae stars in the LMC from OGLE-III

International Nuclear Information System (INIS)

Chen Bing-Qiu; Jiang Bi-Wei; Yang Ming

2013-01-01

A systematic study of RR Lyrae stars is performed using a selected sample of 655 objects in the Large Magellanic Cloud (LMC) with long-term observations and numerous measurements from the Optical Gravitational Lensing Experiment III project. The phase dispersion method and linear superposition of the harmonic oscillations are used to derive the pulsation frequency and properties of light variation. It is found that a dichotomy exists in Oosterhoff Type I and Oosterhoff Type II for RR Lyrae stars in the LMC. Due to our strict criteria for identifying a frequency, a lower limit for the incidence rate of Blazhko modulation in the LMC is estimated in various subclasses of RR Lyrae stars. For fundamental-mode RR Lyrae stars, the rate of 7.5% is smaller than the previous result. In the case of the first-overtone RR Lyrae variables, the rate of 9.1% is relatively high. In addition to the Blazhko variables, 15 objects are identified to pulsate in the fundamental/first-overtone double mode. Furthermore, four objects show a period ratio around 0.6, which makes them very likely to be rare pulsators in the fundamental/second-overtone double mode. (research papers)

RR Lyrae Stars in M4

Science.gov (United States)

Kuehn, Charles A.; Moskalik, Pawel; Drury, Jason A.

2017-10-01

Observations by Kepler/K2 have revolutionized the study of RR Lyrae stars by allowing the detection of new phenomna, such as low amplitude additional modes and period doubling, which had not previously been seen from the ground. During campaign 2, K2 observed the globular cluster M4, providiing the first opportunity to study a sizeable group of RR Lyrae stars that belong to a single population; the other RR Lyrae stars that have been observed from space are field stars in the galactic halo and thus belong to an assortment of populations. In this poster we present the results of our study of the RR Lyrae variables in M4 from K2 photometry. We have identified additional, low amplitude pulsation modes in both observed RRc stars. In 3 RRab stars we have found the Blazhko effect with periods of 16.6d, 22.4d, and 44.5d.

RR Lyrae Stars in M4

Directory of Open Access Journals (Sweden)

Kuehn Charles A

2017-01-01

Full Text Available Observations by Kepler/K2 have revolutionized the study of RR Lyrae stars by allowing the detection of new phenomna, such as low amplitude additional modes and period doubling, which had not previously been seen from the ground. During campaign 2, K2 observed the globular cluster M4, providiing the first opportunity to study a sizeable group of RR Lyrae stars that belong to a single population; the other RR Lyrae stars that have been observed from space are field stars in the galactic halo and thus belong to an assortment of populations. In this poster we present the results of our study of the RR Lyrae variables in M4 from K2 photometry. We have identified additional, low amplitude pulsation modes in both observed RRc stars. In 3 RRab stars we have found the Blazhko effect with periods of 16.6d, 22.4d, and 44.5d.

The Properties of Long Period Variables in the LMC from MACHO

Energy Technology Data Exchange (ETDEWEB)

Fraser, O J; Hawley, S L; Cook, K H

2008-05-06

We present a new analysis of the long period variables in the Large Magellanic Cloud from the MACHO Variable Star Catalog. Three-quarters of our sample of evolved, variable stars have periodic light curves. We characterize the stars in our sample using the multiple periods found in their frequency spectra. Additionally, we use single-epoch 2MASS measurements to construct the average infrared light curves for different groups of these stars. Comparison with evolutionary models shows that stars on the RGB or the Early AGB often show non-periodic variability, but begin to pulsate with periods on the two shortest period-luminosity sequences (1 & 2) when they brighten to K{sub s} {approx} 13. The stars on the Thermally Pulsing AGB are more likely to pulsate with longer periods that lie on the next two P-L sequences (3 & 4), including the sequence associated with the Miras in the LMC. The Petersen diagram and its variants show that multi-periodic stars on each pair of these sequences (3 & 4, and 1 & 2), typically pulsate with periods associated only with that pair. The periods in these multi-periodic stars become longer and stronger as the star evolves. We further constrain the mechanism behind the long secondary periods (LSPs) seen in half of our sample, and find that there is a close match between the luminosity functions of the LSP stars and all of the stars in our sample, and that these star's pulsation amplitudes are relatively wavelength independent. Although this is characteristic of stellar multiplicity, the large number of these variables is problematic for that explanation.

A new interpretation of luminous blue stars

International Nuclear Information System (INIS)

Stothers, R.

1976-01-01

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's new radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large ''bump'' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot, diffuse stellar envelopes (typically those in which L/M>10 3 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than approx.20 M/sub sun/, beginning at M/sub v/=-4.5 and Sp=B1. They also predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized nonadiabatic pulsation theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsation or convective modes)

Variability search in M 31 using principal component analysis and the Hubble Source Catalogue

Science.gov (United States)

Moretti, M. I.; Hatzidimitriou, D.; Karampelas, A.; Sokolovsky, K. V.; Bonanos, A. Z.; Gavras, P.; Yang, M.

2018-06-01

Principal component analysis (PCA) is being extensively used in Astronomy but not yet exhaustively exploited for variability search. The aim of this work is to investigate the effectiveness of using the PCA as a method to search for variable stars in large photometric data sets. We apply PCA to variability indices computed for light curves of 18 152 stars in three fields in M 31 extracted from the Hubble Source Catalogue. The projection of the data into the principal components is used as a stellar variability detection and classification tool, capable of distinguishing between RR Lyrae stars, long-period variables (LPVs) and non-variables. This projection recovered more than 90 per cent of the known variables and revealed 38 previously unknown variable stars (about 30 per cent more), all LPVs except for one object of uncertain variability type. We conclude that this methodology can indeed successfully identify candidate variable stars.

An AO-assisted Variability Study of Four Globular Clusters

Science.gov (United States)

Salinas, R.; Contreras Ramos, R.; Strader, J.; Hakala, P.; Catelan, M.; Peacock, M. B.; Simunovic, M.

2016-09-01

The image-subtraction technique applied to study variable stars in globular clusters represented a leap in the number of new detections, with the drawback that many of these new light curves could not be transformed to magnitudes due to severe crowding. In this paper, we present observations of four Galactic globular clusters, M 2 (NGC 7089), M 10 (NGC 6254), M 80 (NGC 6093), and NGC 1261, taken with the ground-layer adaptive optics module at the SOAR Telescope, SAM. We show that the higher image quality provided by SAM allows for the calibration of the light curves of the great majority of the variables near the cores of these clusters as well as the detection of new variables, even in clusters where image-subtraction searches were already conducted. We report the discovery of 15 new variables in M 2 (12 RR Lyrae stars and 3 SX Phe stars), 12 new variables in M 10 (11 SX Phe and 1 long-period variable), and 1 new W UMa-type variable in NGC 1261. No new detections are found in M 80, but previous uncertain detections are confirmed and the corresponding light curves are calibrated into magnitudes. Additionally, based on the number of detected variables and new Hubble Space Telescope/UVIS photometry, we revisit a previous suggestion that M 80 may be the globular cluster with the richest population of blue stragglers in our Galaxy. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

Short-Period Binary Stars: Observations, Analyses, and Results

CERN Document Server

Milone, Eugene F; Hobill, David W

2008-01-01

Short-period binaries run the gamut from widely separated stars to black-hole pairs; in between are systems that include neutron stars and white dwarfs, and partially evolved systems such as tidally distorted and over-contact systems. These objects represent stages of evolution of binary stars, and their degrees of separation provide critical clues to how their evolutionary paths differ from that of single stars. The widest and least distorted systems provide astronomers with the essential precise data needed to study all stars: mass and radius. The interactions of binary star components, on the other hand, provide a natural laboratory to observe how the matter in these stars behaves under different and often varying physical conditions. Thus, cataclysmic variables with and without overpoweringly strong magnetic fields, and stars with densities from that found in the Sun to the degenerate matter of white dwarfs and the ultra-compact states of neutron stars and black holes are all discussed. The extensive inde...

Variability of Massive Young Stellar Objects in Cygnus-X

Science.gov (United States)

Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

2013-01-01

Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

On the model of symbiotic stars

International Nuclear Information System (INIS)

Tutukov, A.V.; Yungelson, L.R.

1982-01-01

The authors discuss conditions necessary for appearance and discovery of the symbiotic star phenomenon within the model of a binary consisting of a red (super)giant 3 solar masses not filling the Roche lobe and of an accreting hot degenerate CO-dwarf 0.8 solar masses. Within this model ''classical'' symbiotic stars may exist only within a narrow region of mass accretion rates and separations of components: 10 -7 approximately -7 solar masses/y and 3x10 13 approximately 14 cm. The evolutionary status of symbiotic stars and related objects and the mechanisms of their variability are discussed. (Auth.)

SALT Spectroscopy of Evolved Massive Stars

Science.gov (United States)

Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

2017-06-01

Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

Einstein x-ray observations of cataclysmic variables

International Nuclear Information System (INIS)

Mason, K.O.; Cordova, F.A.

1982-01-01

Observations with the imaging x-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity x-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars

VizieR Online Data Catalog: Mira stars discovered in LAMOST DR4 (Yao+, 2017)

Science.gov (United States)

Yao, Y.; Liu, C.; Deng, L.; de Grijs, R.; Matsunaga, N.

2017-10-01

By the end of 2016 March, the wide-field Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) DR4 catalog had accumulated 7681185 spectra (R=1800), of which 6898298 were of stars. We compiled a photometrically confirmed sample of Mira variables from the Kiso Wide-Field Camera (KWFC) Intensive Survey of the Galactic Plane (KISOGP; Matsunaga 2017, arXiv:1705.08567), the American Association of Variable Star Observers (AAVSO) International Database Variable Star Index (VSX; Watson 2006, B/vsx, version 2017-05-02; we selected stars of variability type "M"), and the SIMBAD Astronomical Database. We first cross-matched the KISOGP and VSX Miras with the LAMOST DR4 catalog. Finally, we cross-matched the DR4 catalog with the SIMBAD database. See section 2. (1 data file).

Heartbeat Stars and the Ringing of Tidally Induced Pulsations

OpenAIRE

Hambleton, K.; Kurtz, D.; Prša, A.; Fuller, J.; Thompson, S.

2015-01-01

With the advent of high precision photometry from satellites such as Kepler and CoRoT, a whole new layer of interesting and astounding astronomical objects has been revealed: heartbeat stars are a prime example of such objects. Heartbeat stars are eccentric ellipsoidal variables that undergo strong tidal interactions at the time of closest approach, when the stars are almost in contact. These interactions cause a significant variation in the surface areas of the stars and are observed in the ...

A new search for R Coronae Borealis stars in the SMC

Directory of Open Access Journals (Sweden)

Nikzat Fatemeh

2017-01-01

Full Text Available R Coronae Borealis (RCB stars are rare, and their evolutionary origin is not well understood. Since they are obscured due to formation of carbon dust around the star during their mass loss events, RCB stars can be classified as self-eclipsing variable stars. The purpose of this work is to present a new search for RCB stars in the Small Magellanic Cloud (SMC, by analysing VI data from the OGLE project.

THE DISK POPULATION OF THE TAURUS STAR-FORMING REGION

International Nuclear Information System (INIS)

Luhman, K. L.; Allen, P. R.; Espaillat, C.; Hartmann, L.; Calvet, N.

2010-01-01

We have analyzed nearly all images of the Taurus star-forming region at 3.6, 4.5, 5.8, 8.0, and 24 μm that were obtained during the cryogenic mission of the Spitzer Space Telescope (46 deg 2 ) and have measured photometry for all known members of the region that are within these data, corresponding to 348 sources, or 99% of the known stellar population. By combining these measurements with previous observations with the Spitzer Infrared Spectrograph and other facilities, we have classified the members of Taurus according to whether they show evidence of circumstellar disks and envelopes (classes I, II, and III). Through these classifications, we find that the disk fraction in Taurus, N(II)/N(II+III), is ∼75% for solar-mass stars and declines to ∼45% for low-mass stars and brown dwarfs (0.01-0.3 M sun ). This dependence on stellar mass is similar to that measured for Chamaeleon I, although the disk fraction in Taurus is slightly higher overall, probably because of its younger age (1 Myr versus 2-3 Myr). In comparison, the disk fraction for solar-mass stars is much lower (∼20%) in IC 348 and σ Ori, which are denser than Taurus and Chamaeleon I and are roughly coeval with the latter. These data indicate that disk lifetimes for solar-mass stars are longer in star-forming regions that have lower stellar densities. Through an analysis of multiple epochs of Spitzer photometry that are available for ∼200 Taurus members, we find that stars with disks exhibit significantly greater mid-infrared (mid-IR) variability than diskless stars, which agrees with the results of similar variability measurements for a smaller sample of stars in Chamaeleon I. The variability fraction for stars with disks is higher in Taurus than in Chamaeleon I, indicating that the IR variability of disks decreases with age. Finally, we have used our data in Taurus to refine the observational criteria for primordial, evolved, and transitional disks. The ratio of the number of evolved and

Multiple Stars Across the H-R Diagram

CERN Document Server

Hubrig, Swetlana; Tokovinin, Andrei; Proceedings of the ESO Workshop held in Garching, Germany, 12-15 July 2005

2008-01-01

Stars show a marked tendency to be in systems of different multiplicity, ranging from simple binaries and triples to globular clusters with several 10,000's of stars. The formation and evolution of multiple systems remains a challenging part of astrophysics, and the contributions in this book report on the significant progress that had been made in this research field in the last years. The reader will find a variety of research topics addressed, such as the dynamical evolution in multiple stars, the effects of the environment on multiple system parameters, stellar evolution within multiple stars, multiplicity of massive stars, pre-main sequence and intermediate mass stars, multiplicity of low-mass stars from embedded protostars to open clusters, and brown dwarfs and extrasolar planets in multiples. This book presents the proceedings of the ESO Workshop on Multiple Stars across the H-R Diagram held in the summer of 2005.

Hydroclimatic variability and predictability: a survey of recent research

Directory of Open Access Journals (Sweden)

R. D. Koster

2017-07-01

Full Text Available Recent research in large-scale hydroclimatic variability is surveyed, focusing on five topics: (i variability in general, (ii droughts, (iii floods, (iv land–atmosphere coupling, and (v hydroclimatic prediction. Each surveyed topic is supplemented by illustrative examples of recent research, as presented at a 2016 symposium honoring the career of Professor Eric Wood. Taken together, the recent literature and the illustrative examples clearly show that current research into hydroclimatic variability is strong, vibrant, and multifaceted.

Deformation quantization with separation of variables of an endomorphism bundle

OpenAIRE

Karabegov, Alexander

2013-01-01

Given a holomorphic Hermitian vector bundle and a star-product with separation of variables on a pseudo-Kaehler manifold, we construct a star product on the sections of the endomorphism bundle of the dual bundle which also has the appropriately generalized property of separation of variables. For this star product we prove a generalization of Gammelgaard's graph-theoretic formula.

How bright planets became dim stars: planetary speculations in John Herschel's double star astronomy.

Science.gov (United States)

Case, Stephen

2014-03-01

Previous research on the origins of double star astronomy in the early nineteenth century emphasized the role mathematical methods and instrumentation played in motivating early observations of these objects. The work of the British astronomer John Herschel, however, shows that questions regarding the physical nature of double stars were also important. In particular, an analysis of John Herschel's early work on double stars illustrates the way in which speculations regarding these objects were shaped by assumptions of the properties of stars themselves. For Herschel, a major consideration in double star astronomy was distinguishing between types of double stars. Optical doubles were useful in determining parallax while binary doubles were not. In practice, classification of a specific double star pair into one of these categories was based on the assumption that stars were of approximately the same luminosity and thus differences in relative brightness between stars were caused by difference in distances. Such assumptions, though ultimately abandoned, would lead Herschel in the 1830s to advance the possibility that the dim companion stars in certain double star pairs were not stars at all but in fact planets. Copyright © 2014 Elsevier Ltd. All rights reserved.

Veiling and Accretion Around the Young Binary Stars S and VV Corona Australis

Science.gov (United States)

Sullivan, Kendall; Prato, Lisa; Avilez, Ian

2018-01-01

S CrA and VV CrA are two young binary star systems with separations of 170 AU and 250 AU, respectively, in the southern star-forming region Corona Australis. The spectral types of the four stars in these two systems are similar, approximately K7 to M1, hence the stellar masses are also similar. The study of young stars just emerging from their natal cloud cores at the very limits of observability allows us to probe the extreme environments in which planet formation begins to occur. Stars in this early evolutionary stage can have circumstellar or circumbinary disks, and sometimes remnants of the envelopes which surrounded them during the protostellar stage. Envelopes accrete onto disks and disks in turn accrete onto the central stars, triggering elevated continuum emission, line emission, outflows, and stellar winds. This violent stage marks the onset of the epoch of planet formation. Using high-resolution near-infrared, H-band spectroscopy from the Keck II telescope using the NIRSPEC instrument over 4-6 epochs, we are probing the chaotic environment surrounding the four stars in these systems. We determine the spectral types for VV CrA A and B for the first time, and examine the variable veiling and emission occurring around each of these stars. This research was supported in part by NSF grants AST-1461200 and AST-1313399.

Flaring red dwarf stars: news from Crimea

International Nuclear Information System (INIS)

Gershberg, Roald E

1998-01-01

Important phenomena are briefly described which have recently been discovered in the Crimean studies of flaring red dwarf stars believed to be the most common type of variable stars in the Galaxy. These phenomena include (i) long-lived radiation from a blueshifted component in the ionized-helium λ 4686 A emission line in the active state of one such star, (ii) a long-lived absorption component in the stellar flare light curves with a lifetime exceeding that of the conventional flare emission, and (iii) solarcycle-like activity periodicity of the star EV Lac, whose mass is only 0.3 solar masses. In theoretical terms, a red dwarf star spot model is constructed which, in contrast to the commonly accepted model, agrees well with the solar spot picture. (physics of our days)

Flaring red dwarf stars: news from Crimea

Energy Technology Data Exchange (ETDEWEB)

Gershberg, Roald E [Crimean Astrophysical Observatory, Nauchnyi, Crimea (Ukraine)

1998-08-31

Important phenomena are briefly described which have recently been discovered in the Crimean studies of flaring red dwarf stars believed to be the most common type of variable stars in the Galaxy. These phenomena include (i) long-lived radiation from a blueshifted component in the ionized-helium {lambda} 4686 A emission line in the active state of one such star, (ii) a long-lived absorption component in the stellar flare light curves with a lifetime exceeding that of the conventional flare emission, and (iii) solarcycle-like activity periodicity of the star EV Lac, whose mass is only 0.3 solar masses. In theoretical terms, a red dwarf star spot model is constructed which, in contrast to the commonly accepted model, agrees well with the solar spot picture. (physics of our days)

Asteroseismology of White Dwarf Stars

Science.gov (United States)

Hansen, Carl J.

1997-01-01

The primary purpose of this investigation has been to study various aspects of multimode pulsations in variable white dwarfs. In particular, nonlinear interactions among pulsation modes in white dwarfs (and, to some extent, in other variable stars), analysis of recent observations where such interactions are important, and preliminary work on the effects of crystallization in cool white dwarfs are reported.

A search for OH emission from symbiotic stars

International Nuclear Information System (INIS)

Norris, R.P.; Haynes, R.F.; Wright, A.E.

1984-01-01

A search was made for OH maser emission from a sample of 16 symbiotic stars. This sample was selected on the basis of infrared optical depth and variability, so that the stars within it have circumstellar shells similar to those seen in OH/IR and OH/Mira stars. There were no significant detections, except for one unassociated background source, and it is concluded that the presence of a hot binary companion inhibits any possible OH maser action

SPITZER SAGE-SMC INFRARED PHOTOMETRY OF MASSIVE STARS IN THE SMALL MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Bonanos, A. Z.; Lennon, D. J.; Massa, D. L.

2010-01-01

We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 μm in the UBVIJHK s +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 μm in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A and F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.

Symbiotic stars - a binary model with super-critical accretion

Energy Technology Data Exchange (ETDEWEB)

Bath, G T [National Radio Astronomy Observatory, Charlottesville, Va. (USA)

1977-01-01

The structure of symbiotic variables is discussed in terms of a binary model. Disc accretion by a main sequence star or white dwarf at rates close to the Eddington limit produces an ultraviolet continuum source near the accreting star surface. This generates a variable, radiatively-driven, out-flowing wind. The wind is optically thick and the disc luminosity is absorbed and scattered and thus degraded into the optical region. Variations in the rate of mass loss in the wind lead to optical eruptions through shifts in the position of, and conditions in, the last scattering surface. The behaviour of Z And determined by Boyarchuk is shown to be in agreement with such a model. The conditions in the out-flowing wind are discussed. Limits on the mass loss rate are derived from conditions at the surface of the accreting star. It is suggested that variable out-flow in the wind is generated by fluctuations in disc luminosity produced by changes in the giant companions rate of mass transfer. The relation between symbiotic variables and classical and dwarf novae is discussed.

Nearby Hot Stars May Change Our View of Distant Sources

Science.gov (United States)

Kohler, Susanna

2017-07-01

As if it werent enough that quasars distant and bright nuclei of galaxies twinkle of their own accord due to internal processes, nature also provides another complication: these distant radio sources can also appear to twinkle because of intervening material between them and us. A new study has identified a possible source for the material getting in the way.Unexplained VariabilityA Spitzer infrared view of the Helix nebula, which contains ionized streamers of gas extending radially outward from the central star. [NASA/JPL-Caltech/Univ. of Ariz.]Distant quasars occasionally display extreme scintillation, twinkling with variability timescales shorter than a day. This intra-day variability is much greater than we can account for with standard models of the interstellar medium lying between the quasar and us. So what could cause this extreme scattering instead?The first clue to this mystery came from the discovery of strong variability in the radio source PKS 1322110. In setting up follow-up observations of this object, Mark Walker (Manly Astrophysics, Australia) and collaborators noticed that, in the plane of the sky, PKS 1322110 lies very near the bright star Spica. Could this be coincidence, or might this bright foreground star have something to do with the extreme scattering observed?Diagram explaining the source of the intra-day radio source variability as intervening filaments surrounding a hot star. [M. Walker/CSIRO/Manly Astrophysics]Swarms of ClumpsWalker and collaborators put forward a hypothesis: perhaps the ultraviolet photons of nearby hot stars ionize plasma around them, which in turn causes the extreme scattering of the distant background sources.As a model, the authors consider the Helix Nebula, in which a hot, evolved star is surrounded by cool globules of molecular hydrogen gas. The radiation from the star hits these molecular clumps, dragging them into long radial streamers and ionizing their outer skins.Though the molecular clumps in the Helix

Deformation quantization with separation of variables of an endomorphism bundle

Science.gov (United States)

Karabegov, Alexander

2014-01-01

Given a holomorphic Hermitian vector bundle E and a star-product with separation of variables on a pseudo-Kähler manifold, we construct a star product on the sections of the endomorphism bundle of the dual bundle E∗ which also has the appropriately generalized property of separation of variables. For this star product we prove a generalization of Gammelgaard's graph-theoretic formula.

Targeted Research and Technology Within NASA's Living With a Star Program

Science.gov (United States)

Antiochos, Spiro; Baker, Kile; Bellaire, Paul; Blake, Bern; Crowley, Geoff; Eddy, Jack; Goodrich, Charles; Gopalswamy, Nat; Gosling, Jack; Hesse, Michael

2004-01-01

Targeted Research & Technology (TR&T) NASA's Living With a Star (LWS) initiative is a systematic, goal-oriented research program targeting those aspects of the Sun-Earth system that affect society. The Targeted Research and Technology (TR&T) component of LWS provides the theory, modeling, and data analysis necessary to enable an integrated, system-wide picture of Sun-Earth connection science with societal relevance. Recognizing the central and essential role that TR&T would have for the success of the LWS initiative, the LWS Science Architecture Team (SAT) recommended that a Science Definition Team (SDT), with the same status as a flight mission definition team, be formed to design and coordinate a TR&T program having prioritized goals and objectives that focused on practical societal benefits. This report details the SDT recommendations for the TR&T program.

The Cluster AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster M22

Science.gov (United States)

Rozyczka, M.; Thompson, I. B.; Pych, W.; Narloch, W.; Poleski, R.; Schwarzenberg-Czerny, A.

2017-09-01

The field of the globular cluster M22 (NGC 6656) was monitored between 2000 and 2008 in a search for variable stars. BV light curves were obtained for 359 periodic, likely periodic, and long-term variables, 238 of which are new detections. 39 newly detected variables, and 63 previously known ones are members or likely members of the cluster, including 20 SX Phe, 10 RRab and 16 RRc type pulsators, one BL Her type pulsator, 21 contact binaries, and 9 detached or semi-detached eclipsing binaries. The most interesting among the identified objects are V112 - a bright multimode SX Phe pulsator, V125 - a β Lyr type binary on the blue horizontal branch, V129 - a blue/yellow straggler with a W UMa-like light curve, located halfway between the extreme horizontal branch and red giant branch, and V134 - an extreme horizontal branch object with P=2.33 d and a nearly sinusoidal light curve. All four of them are proper motion members of the cluster. Among nonmembers, a P=2.83 d detached eclipsing binary hosting a δ Sct type pulsator was found, and a peculiar P=0.93 d binary with ellipsoidal modulation and narrow minimum in the middle of one of the descending shoulders of the sinusoid. We also collected substantial new data for previously known variables. In particular we revise the statistics of the occurrence of the Blazhko effect in RR Lyr type variables of M22.

Search for rapid variability of 53 Cam

International Nuclear Information System (INIS)

Zverko, J.

1982-01-01

Photoelectric observations of magnetic Ap star 53 Cam made at the Skalnate Pleso Observatory in 1978 and 1979 are analyzed from the point of view of rapid variability. The observations were made with an intermediate passband filter, effective wavelength 526 nm. Besides the differences msub(53Cam)-msub(Comp), the behaviour was also investigated of the deflections for the comparison star during the observation runs. A strong correlation between the behaviour of the comparison and variable star light curve was found and the appearance differs from night to night depending on atmospheric conditions. Each observation run is analyzed in detail and it was concluded that all observed variations are only apparent and due to the variability of atmospheric extinction above the observation site. (author)

Study on the flare stars in the Taurus region

International Nuclear Information System (INIS)

Khodzhaev, A.S.

1986-01-01

The results of the search of flare stars and their photometric, Hsub(α)-spectroscopic and statistical study in the Taurus are presented. By means of photographic observations carried out during 1980-1984, 92 new flare stars were discovered, 13 of which are known Orion Population variables, and 16 repeated flare-ups among 13 known flare stars. Spatial distribution of these stars was considered and the problem of their membership was discussed. Comparative analysis of the data of flare stars in the Taurus with that of other systems has been carried out. The Herzsprung-Russel and two-colour (U-B, B-V) diagrams for the Taurus flare stars are similar to the diagrams of stellar clusters and associations (Pleiades, Orion etc.). The estimated total number of flare stars in this region is larger than 500

The evolutionary state of the Beta Canis Majoris variables

International Nuclear Information System (INIS)

Shobbrook, R.R.

1978-01-01

New β photometry is presented for all the known β Canis Majoris variables and for other bright early B stars observable from the southern hemisphere which were close to the β CMa stars in a β/[c 1 ] diagram published earlier. The new β values are accurate to +- 0.002 or 0.003 mag and enable the 'instability strip' along which the variables lie to be defined much more precisely. Several of the other B stars also lie in the strip; most of these have already been found to be non-variable in a subsidiary observing programme. (author)

Photometric Modelling of Close Binary Star CN And DMZ Jassur & A ...

Indian Academy of Sciences (India)

system based upon comparison star reading and standard stars observations. Standard magnitudes and colors of variable stars in different phases are given in Table 2. Figures 1 and 2 show the corrected light curves. The light curves are obviously asymmetric, with the primary maximum (phase 0.25) being brighter than the ...

The mysterious SU UMa stars

International Nuclear Information System (INIS)

Charles, P.A.

1990-01-01

This paper discusses the characteristics and the source of energy of the explosive stars called cataclysmic variables (CVs), with special attention given to the SU UMa stars, which represent CVs which have disks. In SU UMa binaries, a gas stream from a cool reddish star hits an accretion disk spiraling around a white dwarf. The impact of the stream produces a bright 'hot spot' on the edge of the disk, seen only when the system is quiescent and the disk is relatively dim (during outbursts, the hot spot is swamped by the light of the disk itself). The principal source of energy and light of most CVs is the gravitational potential energy released by matter falling from the dim reddish companion onto the white dwarf. The mechanism involved in the overflow of the reddish star is believed to be magnetic braking. Simulations are presented that explain the SU UMa phenomena and which may be applicable to other high-mass-ratio interacting binaries

Discovery of new dipper stars with K2: a window into the inner disc region of T Tauri stars

Science.gov (United States)

Hedges, Christina; Hodgkin, Simon; Kennedy, Grant

2018-05-01

In recent years, a new class of young stellar object (YSO) has been defined, referred to as dippers, where large transient drops in flux are observed. These dips are too large to be attributed to stellar variability, last from hours to days and can reduce the flux of a star by 10-50 per cent. This variability has been attributed to occultations by warps or accretion columns near the inner edge of circumstellar discs. Here, we present 95 dippers in the Upper Scorpius association and ρ Ophiuchus cloud complex found in K2 Campaign 2 data using supervised machine learning with a random forest classifier. We also present 30 YSOs that exhibit brightening events on the order of days, known as bursters. Not all dippers and bursters are known members, but all exhibit infrared excesses and are consistent with belonging to either of the two young star-forming regions. We find 21.0 ± 5.5 per cent of stars with discs are dippers for both regions combined. Our entire dipper sample consists only of late-type (KM) stars, but we show that biases limit dipper discovery for earlier spectral types. Using the dipper properties as a proxy, we find that the temperature at the inner disc edge is consistent with interferometric results for similar and earlier type stars.

Classification of O Stars in the Yellow-Green: The Exciting Star VES 735

Science.gov (United States)

Kerton, C. R.; Ballantyne, D. R.; Martin, P. G.

1999-05-01

Acquiring data for spectral classification of heavily reddened stars using traditional criteria in the blue-violet region of the spectrum can be prohibitively time consuming using small to medium sized telescopes. One such star is the Vatican Observatory emission-line star VES 735, which we have found excites the H II region KR 140. In order to classify VES 735, we have constructed an atlas of stellar spectra of O stars in the yellow-green (4800-5420 Å). We calibrate spectral type versus the line ratio He I lambda4922:He II lambda5411, showing that this ratio should be useful for the classification of heavily reddened O stars associated with H II regions. Application to VES 735 shows that the spectral type is O8.5. The absolute magnitude suggests luminosity class V. Comparison of the rate of emission of ionizing photons and the bolometric luminosity of VES 735, inferred from radio and infrared measurements of the KR 140 region, to recent stellar models gives consistent evidence for a main-sequence star of mass 25 M_solar and age less than a few million years with a covering factor 0.4-0.5 by the nebular material. Spectra taken in the red (6500-6700 Å) show that the stellar Hα emission is double-peaked about the systemic velocity and slightly variable. Hβ is in absorption, so that the emission-line classification is ``(e)''. However, unlike the case of the more well-known O(e) star zeta Oph, the emission from VES 735 appears to be long-lived rather than episodic.

Does the Australasian "Health Star Rating" Front of Pack Nutritional Label System Work?

Science.gov (United States)

Hamlin, Robert; McNeill, Lisa

2016-06-01

This article describes an experiment to measure the impact of the Australasian "Health Star Rating" front of pack nutritional label system on consumer choice behaviour. This system presents a one-half to five star rating of nutritional quality via the front facings of food product packages. While this system has been recently rolled out across Australasia, no test of its impact on food choice has been conducted. A sample of 1200 consumers was recruited on exit from supermarkets in New Zealand. A 2 × 2 factorial design was used with two levels of cold cereal product nutritional status (high, five star/low, two star) and two levels of the Health Star Rating label (present/absent). The dependent variable was revealed choice behaviour. The results indicated that the presence of the label had a significant depressive effect on consumer preference, but that this impact was not moderated in any way by the nutritional status expressed by the label. The result represents a significant functional failure of the Health Star Rating label in this research environment. The nature of the failure is consistent with the consumers processing the label in much the same way as the nominal brand cues that dominate the retail food packaging.

VARIABILITY OF OPTICAL COUNTERPARTS IN THE CHANDRA GALACTIC BULGE SURVEY

Energy Technology Data Exchange (ETDEWEB)

Britt, C. T.; Hynes, R. I.; Johnson, C. B.; Baldwin, A.; Collazzi, A.; Gossen, L. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Jonker, P. G.; Torres, M. A. P. [SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht (Netherlands); Nelemans, G. [Department of Astrophysics, IMAPP, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ, Nijmegen (Netherlands); Maccarone, T. [Department of Physics, Texas Tech University, Box 41051, Science Building, Lubbock, TX 79409-1051 (United States); Steeghs, D.; Greiss, S. [Astronomy and Astrophysics, Department of Physics, University of Warwick, Coventry, CV4 7AL (United Kingdom); Heinke, C. [Department of Physics, University of Alberta, CCIS 4-183, Edmonton, AB T6G 2E1 (Canada); Bassa, C. G. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); Villar, A. [Department of Physics, Massachussettes Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307 (United States); Gabb, M. [Department of Physics, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431-0991 (United States)

2014-09-01

We present optical light curves of variable stars consistent with the positions of X-ray sources identified with the Chandra X-ray Observatory for the Chandra Galactic Bulge Survey (GBS). Using data from the Mosaic-II instrument on the Blanco 4 m Telescope at CTIO, we gathered time-resolved photometric data on timescales from ∼2 hr to 8 days over the 3/4 of the X-ray survey containing sources from the initial GBS catalog. Among the light curve morphologies we identify are flickering in interacting binaries, eclipsing sources, dwarf nova outbursts, ellipsoidal variations, long period variables, spotted stars, and flare stars. Eighty-seven percent of X-ray sources have at least one potential optical counterpart. Twenty-seven percent of these candidate counterparts are detectably variable; a much greater fraction than expected for randomly selected field stars, which suggests that most of these variables are real counterparts. We discuss individual sources of interest, provide variability information on candidate counterparts, and discuss the characteristics of the variable population.

SINGLE-LINED SPECTROSCOPIC BINARY STAR CANDIDATES IN THE RAVE SURVEY

International Nuclear Information System (INIS)

Matijevic, G.; Zwitter, T.; Bienayme, O.; Siebert, A.; Watson, F. G.; Bland-Hawthorn, J.; Parker, Q. A.; Freeman, K. C.; Gilmore, G.; Grebel, E. K.; Helmi, A.; Munari, U.; Siviero, A.; Navarro, J. F.; Reid, W.; Seabroke, G. M.; Steinmetz, M.; Williams, M.; Wyse, R. F. G.

2011-01-01

Repeated spectroscopic observations of stars in the RAdial Velocity Experiment (RAVE) database are used to identify and examine single-lined binary (SB1) candidates. The RAVE latest internal database (VDR3) includes radial velocities, atmospheric parameters, and other parameters for approximately a quarter of a million different stars with slightly less than 300,000 observations. In the sample of ∼20,000 stars observed more than once, 1333 stars with variable radial velocities were identified. Most of them are believed to be SB1 candidates. The fraction of SB1 candidates among stars with several observations is between 10% and 15% which is the lower limit for binarity among RAVE stars. Due to the distribution of time spans between the re-observation that is biased toward relatively short timescales (days to weeks), the periods of the identified SB1 candidates are most likely in the same range. Because of the RAVE's narrow magnitude range most of the dwarf candidates belong to the thin Galactic disk while the giants are part of the thick disk with distances extending to up to a few kpc. The comparison of the list of SB1 candidates to the VSX catalog of variable stars yielded several pulsating variables among the giant population with radial velocity variations of up to few tens of km s -1 . There are 26 matches between the catalog of spectroscopic binary orbits (S B 9 ) and the whole RAVE sample for which the given periastron time and the time of RAVE observation were close enough to yield a reliable comparison. RAVE measurements of radial velocities of known spectroscopic binaries are consistent with their published radial velocity curves.

A Suzaku, NuSTAR and XMMNewton} view on variable absorption and relativistic reflection in NGC 4151

Science.gov (United States)

Beuchert, T.; Markowitz, A.; Dauser, T.; Garcia, J.; Keck, M.; Wilms, J.; Kadler, M.; Brenneman, L.; Zdziarski, A.

2017-10-01

We disentangle X-ray disk reflection from complex line-of-sight absorption in NGC 4151 using Suzaku, NuSTAR, and XMMNewton}. Extending upon Keck et al. (2015), we develop a physically-motivated baseline model using the latest lamp-post reflection code relxillCp_lp, which includes a Comptonization continuum. We identify two components at heights of 1.2 and 15.0 gravitational radii using a long-look simultaneous Suzaku/NuSTAR observation but argue for a vertically extended corona as opposed to distinct primary sources. We also find two neutral absorbers (one full-covering and one partial-covering), an ionized absorber (log ξ=2.8), and a highly-ionized ultra-fast outflow, all reported previously. All analyzed spectra are well described by this baseline model. The bulk of the spectral variability on time-scales from days to years can be attributed to changes of both neutral absorbers, which are inversely correlated with the hard X-ray continuum flux. The observed evolution is either consistent with changes in the absorber structure (clumpy absorber in the outer BLR or a dusty radiatively driven wind) or a geometrically stable neutral absorber that becomes increasingly ionized at a rising flux level. The soft X-rays below 1 keV are dominated by photoionized emission from extended gas, which may act as a warm mirror for the nuclear radiation.

The Rose-red Glow of Star Formation

Science.gov (United States)

2011-03-01

The vivid red cloud in this new image from ESO's Very Large Telescope is a region of glowing hydrogen surrounding the star cluster NGC 371. This stellar nursery lies in our neighbouring galaxy, the Small Magellanic Cloud. The object dominating this image may resemble a pool of spilled blood, but rather than being associated with death, such regions of ionised hydrogen - known as HII regions - are sites of creation with high rates of recent star birth. NGC 371 is an example of this; it is an open cluster surrounded by a nebula. The stars in open clusters all originate from the same diffuse HII region, and over time the majority of the hydrogen is used up by star formation, leaving behind a shell of hydrogen such as the one in this image, along with a cluster of hot young stars. The host galaxy to NGC 371, the Small Magellanic Cloud, is a dwarf galaxy a mere 200 000 light-years away, which makes it one of the closest galaxies to the Milky Way. In addition, the Small Magellanic Cloud contains stars at all stages of their evolution; from the highly luminous young stars found in NGC 371 to supernova remnants of dead stars. These energetic youngsters emit copious amounts of ultraviolet radiation causing surrounding gas, such as leftover hydrogen from their parent nebula, to light up with a colourful glow that extends for hundreds of light-years in every direction. The phenomenon is depicted beautifully in this image, taken using the FORS1 instrument on ESO's Very Large Telescope (VLT). Open clusters are by no means rare; there are numerous fine examples in our own Milky Way. However, NGC 371 is of particular interest due to the unexpectedly large number of variable stars it contains. These are stars that change in brightness over time. A particularly interesting type of variable star, known as slowly pulsating B stars, can also be used to study the interior of stars through asteroseismology [1], and several of these have been confirmed in this cluster. Variable stars

Theory of neutron star magnetospheres

CERN Document Server

Curtis Michel, F

1990-01-01

An incomparable reference for astrophysicists studying pulsars and other kinds of neutron stars, "Theory of Neutron Star Magnetospheres" sums up two decades of astrophysical research. It provides in one volume the most important findings to date on this topic, essential to astrophysicists faced with a huge and widely scattered literature. F. Curtis Michel, who was among the first theorists to propose a neutron star model for radio pulsars, analyzes competing models of pulsars, radio emission models, winds and jets from pulsars, pulsating X-ray sources, gamma-ray burst sources, and other neutron-star driven phenomena. Although the book places primary emphasis on theoretical essentials, it also provides a considerable introduction to the observational data and its organization. Michel emphasizes the problems and uncertainties that have arisen in the research as well as the considerable progress that has been made to date.

COMPARISON OF KEPLER PHOTOMETRIC VARIABILITY WITH THE SUN ON DIFFERENT TIMESCALES

International Nuclear Information System (INIS)

Basri, Gibor; Walkowicz, Lucianne M.; Reiners, Ansgar

2013-01-01

We utilize Kepler data to study the precision differential photometric variability of solar-type and cooler stars at different timescales, ranging from half an hour to three months. We define a diagnostic that characterizes the median differential intensity change between data bins of a given timescale. We apply the same diagnostics to Solar and Heliospheric Observatory data that has been rendered comparable to Kepler. The Sun exhibits similar photometric variability on all timescales as comparable solar-type stars in the Kepler field. The previously defined photometric ''range'' serves as our activity proxy (driven by starspot coverage). We revisit the fraction of comparable stars in the Kepler field that are more active than the Sun. The exact active fraction depends on what is meant by ''more active than the Sun'' and on the magnitude limit of the sample of stars considered. This active fraction is between a quarter and a third (depending on the timescale). We argue that a reliable result requires timescales of half a day or longer and stars brighter than M Kep of 14, otherwise non-stellar noise distorts it. We also analyze main sequence stars grouped by temperature from 6500 to 3500 K. As one moves to cooler stars, the active fraction of stars becomes steadily larger (greater than 90% for early M dwarfs). The Sun is a good photometric model at all timescales for those cooler stars that have long-term variability within the span of solar variability.

AirSTAR Hardware and Software Design for Beyond Visual Range Flight Research

Science.gov (United States)

Laughter, Sean; Cox, David

2016-01-01

The National Aeronautics and Space Administration (NASA) Airborne Subscale Transport Aircraft Research (AirSTAR) Unmanned Aerial System (UAS) is a facility developed to study the flight dynamics of vehicles in emergency conditions, in support of aviation safety research. The system was upgraded to have its operational range significantly expanded, going beyond the line of sight of a ground-based pilot. A redesign of the airborne flight hardware was undertaken, as well as significant changes to the software base, in order to provide appropriate autonomous behavior in response to a number of potential failures and hazards. Ground hardware and system monitors were also upgraded to include redundant communication links, including ADS-B based position displays and an independent flight termination system. The design included both custom and commercially available avionics, combined to allow flexibility in flight experiment design while still benefiting from tested configurations in reversionary flight modes. A similar hierarchy was employed in the software architecture, to allow research codes to be tested, with a fallback to more thoroughly validated flight controls. As a remotely piloted facility, ground systems were also developed to ensure the flight modes and system state were communicated to ground operations personnel in real-time. Presented in this paper is a general overview of the concept of operations for beyond visual range flight, and a detailed review of the airborne hardware and software design. This discussion is held in the context of the safety and procedural requirements that drove many of the design decisions for the AirSTAR UAS Beyond Visual Range capability.

THE STRUCTURE OF THE STAR-FORMING CLUSTER RCW 38

Energy Technology Data Exchange (ETDEWEB)

Winston, E. [ESA-ESTEC (SRE-SA), Keplerlaan 1, 2201 AZ Noordwijk ZH (Netherlands); Wolk, S. J.; Bourke, T. L.; Spitzbart, B. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Megeath, S. T. [Ritter Observatory, Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Avenue, Toledo, OH 43606 (United States); Gutermuth, R., E-mail: ewinston@rssd.esa.int [Five Colleges Astronomy Department, Smith College, Northampton, MA 01027 (United States)

2011-12-20

We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8 {mu}m) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region. Three subclusters were identified surrounding the central cluster, with massive and variable stars in each subcluster. The central region shows evidence of distinct spatial distributions of the protostars and pre-main-sequence stars. A previously detected IR cluster, DB2001{sub O}bj36, has been established as a subcluster of RCW 38. This suggests that star formation in RCW 38 occurs over a more extended area than previously thought. The gas-to-dust ratio is examined using the X-ray derived hydrogen column density, N{sub H} and the K-band extinction, and found to be consistent with the diffuse interstellar medium, in contrast with Serpens and NGC 1333. We posit that the high photoionizing flux of massive stars in RCW 38 affects the agglomeration of the dust grains.

The mass-metallicity relations for gas and stars in star-forming galaxies: strong outflow versus variable IMF

Science.gov (United States)

Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Comparat, Johan; Gonzalez-Perez, Violeta; Ventura, Paolo

2018-02-01

We investigate the mass-metallicity relations for the gaseous (MZRgas) and stellar components (MZRstar) of local star-forming galaxies based on a representative sample from Sloan Digital Sky Survey Data Release 12. The mass-weighted average stellar metallicities are systematically lower than the gas metallicities. This difference in metallicity increases towards galaxies with lower masses and reaches 0.4-0.8 dex at 109 M⊙ (depending on the gas metallicity calibration). As a result, the MZRstar is much steeper than the MZRgas. The much lower metallicities in stars compared to the gas in low-mass galaxies imply dramatic metallicity evolution with suppressed metal enrichment at early times. The aim of this paper is to explain the observed large difference in gas and stellar metallicity and to infer the origin of the mass-metallicity relations. To this end we develop a galactic chemical evolution model accounting for star formation, gas inflow and outflow. By combining the observed mass-metallicity relation for both gas and stellar components to constrain the models, we find that only two scenarios are able to reproduce the observations. Either strong metal outflow or a steep initial mass function (IMF) slope at early epochs of galaxy evolution is needed. Based on these two scenarios, for the first time we successfully reproduce the observed MZRgas and MZRstar simultaneously, together with other independent observational constraints in the local Universe. Our model also naturally reproduces the flattening of the MZRgas at the high-mass end leaving the MZRstar intact, as seen in observational data.

AAVSO Target Tool: A Web-Based Service for Tracking Variable Star Observations (Abstract)

Science.gov (United States)

Burger, D.; Stassun, K. G.; Barnes, C.; Kafka, S.; Beck, S.; Li, K.

2018-06-01

(Abstract only) The AAVSO Target Tool is a web-based interface for bringing stars in need of observation to the attention of AAVSOís network of amateur and professional astronomers. The site currently tracks over 700 targets of interest, collecting data from them on a regular basis from AAVSOís servers and sorting them based on priority. While the target tool does not require a login, users can obtain visibility times for each target by signing up and entering a telescope location. Other key features of the site include filtering by AAVSO observing section, sorting by different variable types, formatting the data for printing, and exporting the data to a CSV file. The AAVSO Target Tool builds upon seven years of experience developing web applications for astronomical data analysis, most notably on Filtergraph (Burger, D., et al. 2013, Astronomical Data Analysis Software and Systems XXII, Astronomical Society of the Pacific, San Francisco, 399), and is built using the web2py web framework based on the python programming language. The target tool is available at http://filtergraph.com/aavso.

AGB stars as tracers to IC 1613 evolution.

Science.gov (United States)

Hashemi, S. A.; Javadi, A.; van Loon, J. Th.

We are going to apply AGB stars to find star formation history for IC 1613 galaxy; this a new and simple method that works well for nearby galaxies. IC 1613 is a Local Group dwarf irregular galaxy that is located at distance of 750 kpc, a gas rich and isolated dwarf galaxy that has a low foreground extinction. We use the long period variable stars (LPVs) that represent the very final stage of evolution of stars with low and intermediate mass at the AGB phase and are very luminous and cool so that they emit maximum brightness in near-infrared bands. Thus near-infrared photometry with using stellar evolutionary models help us to convert brightness to birth mass and age and from this drive star formation history of the galaxy. We will use the luminosity distribution of the LPVs to reconstruct the star formation history-a method we have successfully applied in other Local Group galaxies. Our analysis shows that the IC 1613 has had a nearly constant star formation rate, without any dominant star formation episode.

Choosing appropriate independent variable in educational experimental research: some errors debunked

Science.gov (United States)

Panjaitan, R. L.

2018-03-01

It is found that a number of quantitative research reports of some beginning researchers, especially undergraduate students, tend to ‘merely’ quantitative with not really proper understanding of variables involved in the research. This paper focuses on some mistakes related to independent variable determination in experimental research in education. With literature research methodology, data were gathered from an undergraduate student’s thesis as a single non-human subject. This data analysis resulted some findings, such as misinterpreted variables that should have represented the research question, and unsuitable calculation of determination coefficient due to incorrect independent variable determination. When a researcher misinterprets data as data that could behave as the independent variable but actually it could not, all of the following data processes become pointless. These problems might lead to inaccurate research conclusion. In this paper, the problems were analysed and discussed. To avert the incorrectness in processing data, it is suggested that undergraduate students as beginning researchers have adequate statistics mastery. This study might function as a resource to researchers in education to be aware to and not to redo similar errors.

Broad-band linear polarization and magnetic intensification in rotating magnetic stars

International Nuclear Information System (INIS)

Degl'Innocenti, M.L.; Calamai, G.; Degl'Innocenti, E.L.; Patriarchi, P.

1981-01-01

Magnetic intensification is proposed as a mechanism to explain the general features of the variable broad-band linear polarization emerging from rotating magnetic stars. This mechanism is studied in detail, and some efforts are made to investigate the wide variety of polarization diagrams that can result from it. Theoretical results are compared with direct observations of the variable magnetic star 53 Cam to determine its geometric and magnetic configuration

Ecology of blue straggler stars

CERN Document Server

Carraro, Giovanni; Beccari, Giacomo

2015-01-01

The existence of blue straggler stars, which appear younger, hotter, and more massive than their siblings, is at odds with a simple picture of stellar evolution. Such stars should have exhausted their nuclear fuel and evolved long ago to become cooling white dwarfs. They are found to exist in globular clusters, open clusters, dwarf spheroidal galaxies of the Local Group, OB associations and as field stars. This book summarises the many advances in observational and theoretical work dedicated to blue straggler stars. Carefully edited extended contributions by well-known experts in the field cover all the relevant aspects of blue straggler stars research: Observations of blue straggler stars in their various environments; Binary stars and formation channels; Dynamics of globular clusters; Interpretation of observational data and comparison with models. The book also offers an introductory chapter on stellar evolution written by the editors of the book.

A ROSAT Survey of Contact Binary Stars

Science.gov (United States)

Geske, M. T.; Gettel, S. J.; McKay, T. A.

2006-01-01

Contact binary stars are common variable stars that are all believed to emit relatively large fluxes of X-rays. In this work we combine a large new sample of contact binary stars derived from the ROTSE-I telescope with X-ray data from the ROSAT All Sky Survey (RASS) to estimate the X-ray volume emissivity of contact binary stars in the Galaxy. We obtained X-ray fluxes for 140 contact binaries from the RASS, as well as two additional stars observed by the XMM-Newton observatory. From these data we confirm the emission of X-rays from all contact binary systems, with typical luminosities of approximately 1.0×1030 ergs s-1. Combining calculated luminosities with an estimated contact binary space density, we find that contact binaries do not have strong enough X-ray emission to account for a significant portion of the Galactic X-ray background.

Do some x-ray stars have white dwarf companions

Science.gov (United States)

Mccollum, Bruce

1995-01-01

Some Be stars which are intermittent X-ray sources may have white dwarf companions rather than neutron stars. It is not possible to prove or rule out the existence of Be + WD systems using X-ray or optical data. However, the presence of a white dwarf could be established by the detection of its EUV continuum shortward of the Be star's continuum turnover at 100 A. Either the detection or the nondetection of Be + WD systems would have implications for models of Be star variability, models of Be binary system formation and evolution, and models of wind-fed accretion.

RR Lyrae stars in and around NGC 6441: signatures of dissolving cluster stars

Science.gov (United States)

Kunder, Andrea

2018-06-01

Detailed elemental abundance patterns of metal-poor ([Fe/H]~ -1 dex) stars in the Galactic bulge indicate that a number of them are consistent with globular cluster (GC) stars and may be former members of dissolved GCs. This would indicate that a few per cent of the Galactic bulge was built up from destruction and/or evaporation of globular clusters. Here an attempt is made to identify such presumptive destroyed stars originating from the massive, inner Galaxy globular cluster NGC~6441 using its rich RR Lyrae variable star (RRL) population. We present radial velocities of forty RRLs centered on the globular cluster NGC~6441. All of the 13 RRLs observed within the cluster tidal radius have velocities consistent with cluster membership, with an average radial velocity of 24 +- 5~km/s and a star-to-star scatter of 11~km/s. This includes two new RRLs that were previously not associated with the cluster. Eight RRLs with radial velocities consistent with cluster membership but up to three time the distance from the tidal radius are also reported. These potential extra-tidal RRLs also have exceptionally long periods, which is a curious characteristic of the NGC~6441 RRL population that hosts RRLs with periods longer than seen anywhere else in the Milky Way. As expected of stripped cluster stars, most are inline with the cluster's orbit. Therefore, either the tidal radius of NGC~6441 is underestimated and/or we are seeing dissolving cluster stars stemming from NGC~6441 that are building up the old spheroidal bulge. Both the mean velocity of the cluster as well as the underlying field population is consistent with belonging to an old spheroidal bulge with low rotation and high velocity dispersion that formed before the bar.

NATO Advanced Research Workshiop on Superdense QCD Matter and Compact Stars

CERN Document Server

Blaschke, David

2006-01-01

This volume covers the main topics in the theory of superdense QCD matter and its application to the astrophysics of compact stars in a comprehensive and yet accessible way. The material is presented as a combination of extensive introductory lectures and more topical contributions. The book is centered around the question whether hypothetical new states of dense matter in the compact star interior could give clues to the explanation of puzzling phenomena such as gamma-ray bursts, pulsar glitches, compact star cooling and gravitational waves.

A study of flare stars in the taurus region

International Nuclear Information System (INIS)

Khodzhaev, A.S.

1986-01-01

The results are given of a search for flare stars in the region of the dark clouds in Taurus together with the results of photometric, H /sub alpha/ -spectroscopic, and statistical investigations of them. Photographic observations during 1980-1984 revealed 92 new flare stars, 13 of which were found to be known Orion variables with 16 repeated flares of 13 previously known flare stars. Their apparent distribution is considered. The question of whether the flare stars belong to a dark cloud is discussed. A comparative analysis of the flare stars in the Taurus region and other aggregates is made. The Hertzsprung-Russell (V, B - V) and two-color (U - B, B - V) diagrams for the flare stars are similar to the corresponding diagrams constructed for star clusters and associations (Pleiades, Orion, etc.). The total number of flare stars in the region of the dark clouds in Taurus is estimated at ≥ 500

The origin of Wolf-Rayet stars

International Nuclear Information System (INIS)

Doom, C.

1987-01-01

The paper reviews the origin of Wolf-Rayet (WR) stars, with emphasis on the so-called Population I WR stars which are associated with the young and luminous stellar population. A description is given of the observational characteristics i.e. classification, luminosities composition, etc. of WR stars. The origin and evolution of WR stars is described, including the single, binary, subtypes and ratio WR/O. The interaction of the WR stars with their environment is discussed with respect to the energy deposition and composition anomalies. A brief account of the discovery of WR stars in other galaxies is given. Finally, some of the main issues in the research into the structure and evolution of WR stars are outlined. (U.K.)

Relationship of classical novae to other eruptive variables

International Nuclear Information System (INIS)

Vogt, N.

1989-01-01

Classical novae are characterized by their well known large-amplitude outbursts, accompanied by the ejection of a shell. The same stars, however, apparently pass through much longer quiescent phases whose duration exceeds that of the outburst phase by a factor ∼ 10 5 and that of historical nova records by a factor 10 2 -10 3 . Therefore a large number of variable stars should exist which actually are classical nova systems but whose last outbursts occurred in prehistoric times. We assume that some of these stars are hidden among the so-called 'nova-lies' in the literature. However some eruptive variables and symbiotic stars, i.e. stars which certainly are not nova remnants, are mentioned. Variables related to classical novae can be divided into three main classes: (i) Potential novae which are possibly classical novae in their quiescent state. Potential novae must share the basic configuration and parameters (orbital period, masses) with classical novae; they must be semi-detached cataclysmic binaries with a white dwarf as primary and a Roche-lobe-filling red dwarf on, or near, the mainsequence as secondary. (ii) Stars which share some outburst characteristics with classical novae without having the same binary configuration. For example recurrent novae with giant secondaries, very slow novae (and symbiotic binary stars). (iii) Stars which are evolutionarily related to classical novae, i.e. which possibly are progenitors or successors of novae in their secular evolution, such as binary nuclei of planetary nebulae and close, but detached, white dwarf-red dwarf pairs (e.g. V 471 Tau), both resulting from common-envelope evolution. These three main groups of nova-related stars are discussed. (author)

Neutron star news and puzzles

International Nuclear Information System (INIS)

Prakash, Madappa

2014-01-01

Gerry Brown has had the most influence on my career in Physics, and my life after graduate studies. This article gives a brief account of some of the many ways in which Gerry shaped my research. Focus is placed on the significant strides on neutron star research made by the group at Stony Brook, which Gerry built from scratch. Selected puzzles about neutron stars that remain to be solved are noted

Solar-Terrestrial and Astronomical Research Network (STAR-Network) - A Meaningful Practice of New Cyberinfrastructure on Space Science

Science.gov (United States)

Hu, X.; Zou, Z.

2017-12-01

For the next decades, comprehensive big data application environment is the dominant direction of cyberinfrastructure development on space science. To make the concept of such BIG cyberinfrastructure (e.g. Digital Space) a reality, these aspects of capability should be focused on and integrated, which includes science data system, digital space engine, big data application (tools and models) and the IT infrastructure. In the past few years, CAS Chinese Space Science Data Center (CSSDC) has made a helpful attempt in this direction. A cloud-enabled virtual research platform on space science, called Solar-Terrestrial and Astronomical Research Network (STAR-Network), has been developed to serve the full lifecycle of space science missions and research activities. It integrated a wide range of disciplinary and interdisciplinary resources, to provide science-problem-oriented data retrieval and query service, collaborative mission demonstration service, mission operation supporting service, space weather computing and Analysis service and other self-help service. This platform is supported by persistent infrastructure, including cloud storage, cloud computing, supercomputing and so on. Different variety of resource are interconnected: the science data can be displayed on the browser by visualization tools, the data analysis tools and physical models can be drived by the applicable science data, the computing results can be saved on the cloud, for example. So far, STAR-Network has served a series of space science mission in China, involving Strategic Pioneer Program on Space Science (this program has invested some space science satellite as DAMPE, HXMT, QUESS, and more satellite will be launched around 2020) and Meridian Space Weather Monitor Project. Scientists have obtained some new findings by using the science data from these missions with STAR-Network's contribution. We are confident that STAR-Network is an exciting practice of new cyberinfrastructure architecture on

VizieR Online Data Catalog: Photometric variability of BeSS-KELT stars (Labadie-Bartz+, 2017)

Science.gov (United States)

Labadie-Bartz, J.; Pepper, J.; McSwain, M. V.; Bjorkman, J. E.; Bjorkman, K. S.; Lund, M. B.; Rodriguez, J. E.; Stassun, K. G.; Stevens, D. J.; James, D. J.; Kuhn, R. B.; Siverd, R. J.; Beatty, T. G.

2018-04-01

Kilodegree Extremely Little Telescope (KELT) is a photometric survey using two small-aperture (42 mm) wide-field (26°x26°) telescopes, with a northern location at Winer Observatory in Arizona in the United States, and a southern location at the South African Astronomical Observatory near Sutherland, South Africa. The Be Star Spectra (BeSS) database is a continually updated catalog that attempts to include all known Be stars, as well as their stellar parameters. This catalog is based primarily on the catalog of classical Be stars published by Jaschek et al. (1982, Cat. III/67) but also includes more recently discovered Be stars from a variety of sources (e.g., Neiner et al. 2005ApJS..156..237N; Martayan et al. 2006A&A...445..931M). From the BeSS database, we compiled a list of all the classical Be stars with 7stars in this sample, 374 are observed by KELT North, 206 are observed by KELT South, and 30 are observed by both KELT North and South (the joint field J06). (1 data file).

Cepheid pulsation theory and multiperiodic cepheid variables

International Nuclear Information System (INIS)

Cox, A.N.; Cox, J.P.

1975-01-01

In this review of the multiperiodic Cepheid variables, the subject matter is divided into four parts. The first discusses general causes of pulsation of Cepheids and other variable stars, and their locations on the H-R diagram. In the second section, the linear adiabatic and nonadiabatic theory calculation of radial pulsation periods and their application to the problem of masses and double-mode Cepheids are reviewed. Periodic solutions, and their stability, of the nonlinear radial pulsation equations for Cepheids and RR Lyrae stars are considered in the third section. The last section provides the latest results on nonlinear, nonperiodic, radial pulsations for Cepheids and RR Lyrae stars. (BJG)

THE INFRARED SPECTRAL PROPERTIES OF MAGELLANIC CARBON STARS

Energy Technology Data Exchange (ETDEWEB)

Sloan, G. C. [Cornell Center for Astrophysics and Planetary Science, Cornell Univ., Ithaca, NY 14853-6801 (United States); Kraemer, K. E. [Institute for Scientific Research, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467 (United States); McDonald, I.; Zijlstra, A. A. [Jodrell Bank Centre for Astrophysics, Univ. of Manchester, Manchester M13 9PL (United Kingdom); Groenewegen, M. A. T. [Koninklijke Sterrenwacht van België, Ringlaan 3, B-1180 Brussels (Belgium); Wood, P. R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Lagadec, E. [Observatoire de la Côte d’Azur, F-06300, Nice (France); Boyer, M. L. [CRESST and Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD, 20771 (United States); Kemper, F.; Srinivasan, S. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan, R.O.C. (China); Matsuura, M. [School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA (United Kingdom); Sahai, R. [Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, Pasadena, CA 91109 (United States); Sargent, B. A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Van Loon, J. Th. [Lennard Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Volk, K., E-mail: sloan@isc.astro.cornell.edu [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)

2016-07-20

The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C{sub 2}H{sub 2} at 7.5 μ m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

THE INFRARED SPECTRAL PROPERTIES OF MAGELLANIC CARBON STARS

International Nuclear Information System (INIS)

Sloan, G. C.; Kraemer, K. E.; McDonald, I.; Zijlstra, A. A.; Groenewegen, M. A. T.; Wood, P. R.; Lagadec, E.; Boyer, M. L.; Kemper, F.; Srinivasan, S.; Matsuura, M.; Sahai, R.; Sargent, B. A.; Van Loon, J. Th.; Volk, K.

2016-01-01

The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C 2 H 2 at 7.5 μ m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

Does the Australasian “Health Star Rating” Front of Pack Nutritional Label System Work?

Directory of Open Access Journals (Sweden)

Robert Hamlin

2016-06-01

Full Text Available This article describes an experiment to measure the impact of the Australasian “Health Star Rating” front of pack nutritional label system on consumer choice behaviour. This system presents a one-half to five star rating of nutritional quality via the front facings of food product packages. While this system has been recently rolled out across Australasia, no test of its impact on food choice has been conducted. A sample of 1200 consumers was recruited on exit from supermarkets in New Zealand. A 2 × 2 factorial design was used with two levels of cold cereal product nutritional status (high, five star/low, two star and two levels of the Health Star Rating label (present/absent. The dependent variable was revealed choice behaviour. The results indicated that the presence of the label had a significant depressive effect on consumer preference, but that this impact was not moderated in any way by the nutritional status expressed by the label. The result represents a significant functional failure of the Health Star Rating label in this research environment. The nature of the failure is consistent with the consumers processing the label in much the same way as the nominal brand cues that dominate the retail food packaging.

Does the Australasian “Health Star Rating” Front of Pack Nutritional Label System Work?

Science.gov (United States)

Hamlin, Robert; McNeill, Lisa

2016-01-01

This article describes an experiment to measure the impact of the Australasian “Health Star Rating” front of pack nutritional label system on consumer choice behaviour. This system presents a one-half to five star rating of nutritional quality via the front facings of food product packages. While this system has been recently rolled out across Australasia, no test of its impact on food choice has been conducted. A sample of 1200 consumers was recruited on exit from supermarkets in New Zealand. A 2 × 2 factorial design was used with two levels of cold cereal product nutritional status (high, five star/low, two star) and two levels of the Health Star Rating label (present/absent). The dependent variable was revealed choice behaviour. The results indicated that the presence of the label had a significant depressive effect on consumer preference, but that this impact was not moderated in any way by the nutritional status expressed by the label. The result represents a significant functional failure of the Health Star Rating label in this research environment. The nature of the failure is consistent with the consumers processing the label in much the same way as the nominal brand cues that dominate the retail food packaging. PMID:27258305

STATISTICAL PROPERTIES OF GALACTIC δ SCUTI STARS: REVISITED

International Nuclear Information System (INIS)

Chang, S.-W.; Kim, D.-W.; Byun, Y.-I.; Protopapas, P.

2013-01-01

We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of δ Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodríguez's work. All the δ Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing δ Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

Photometric and spectroscopic variability of the B5IIIe star HD 171219

Science.gov (United States)

Andrade, L.; Janot-Pacheco, E.; Emilio, M.; Frémat, Y.; Neiner, C.; Poretti, E.; Mathias, P.; Rainer, M.; Suárez, J. C.; Uytterhoeven, K.; Briquet, M.; Diago, P. D.; Fabregat, J.; Gutiérrez-Soto, J.

2017-07-01

We analyzed the star HD 171219, one of the relatively bright Be stars observed in the seismo field of the CoRoT satellite, in order to determine its physical and pulsation characteristics. Classical Be stars are main-sequence objects of mainly B-type, whose spectra show, or have shown at some epoch, Balmer lines in emission and an infrared excess. Both characteristics are attributed to an equatorially concentrated circumstellar disk fed by non-periodic mass-loss episodes (outbursts). Be stars often show nonradial pulsation gravity modes and, as more recently discovered, stochastically excited oscillations. Applying the CLEANEST algorithm to the high-cadence and highly photometrically precise measurements of the HD 171219 light curve led us to perform an unprecedented detailed analysis of its nonradial pulsations. Tens of frequencies have been detected in the object compatible with nonradial g-modes. Additional high-resolution ground-based spectroscopic observations were obtained at La Silla (HARPS) and Haute Provence (SOPHIE) observatories during the month preceding CoRoT observations. Additional information was obtained from low-resolution spectra from the BeSS database. From spectral line fitting we determined physical parameters of the star, which is seen equator-on (I = 90°). We also found in the ground data the same frequencies as in CoRoT data. Additionally, we analyzed the circumstellar activity through the traditional method of violet to red emission Hα line variation. A quintuplet was identified at approximately 1.113 c d-1 (12.88 μHz) with a separation of 0.017 c d-1 that can be attributed to a pulsation degree ℓ 2. The light curve shows six small- to medium-scale outbursts during the CoRoT observations. The intensity of the main frequencies varies after each outburst, suggesting a possible correlation between the nonradial pulsations regime and the feeding of the envelope. The CoRoT space mission was developed and operated by the French space agency

MASSIVE STARS IN THE Cl 1813-178 CLUSTER: AN EPISODE OF MASSIVE STAR FORMATION IN THE W33 COMPLEX

International Nuclear Information System (INIS)

Messineo, Maria; Davies, Ben; Figer, Donald F.; Trombley, Christine; Kudritzki, R. P.; Valenti, Elena; Najarro, F.; Michael Rich, R.

2011-01-01

Young massive (M > 10 4 M sun ) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here, we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main-sequence stars with masses between 25 and 100 M sun . A population with age of 4-4.5 Myr and a mass of ∼10, 000 M sun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex.

DISK-RELATED BURSTS AND FADES IN YOUNG STARS

International Nuclear Information System (INIS)

Findeisen, Krzysztof; Hillenbrand, Lynne; Levitan, David; Sesar, Branimir; Ofek, Eran; Laher, Russ; Surace, Jason

2013-01-01

We present first results from a new, multiyear, time domain survey of young stars in the North America Nebula complex using the Palomar Transient Factory. Our survey is providing an unprecedented view of aperiodic variability in young stars on timescales of days to years. The analyzed sample covers R PTF ≈ 13.5-18 and spans a range of mid-infrared color, with larger-amplitude optical variables (exceeding 0.4 mag root mean squared) more likely to have mid-infrared evidence for circumstellar material. This paper characterizes infrared excess stars with distinct bursts above or fades below a baseline of lower-level variability, identifying 41 examples. The light curves exhibit a remarkable diversity of amplitudes, timescales, and morphologies, with a continuum of behaviors that cannot be classified into distinct groups. Among the bursters, we identify three particularly promising sources that may represent theoretically predicted short-timescale accretion instabilities. Finally, we find that fading behavior is approximately twice as common as bursting behavior on timescales of days to years, although the bursting and fading duty cycle for individual objects often varies from year to year.

The ZZ Ceti stars and the rate of evolution of white dwarfs

International Nuclear Information System (INIS)

Robinson, E.L.; Kepler, S.O.

1980-01-01

The importance of the ZZ Ceti stars, and indeed the importance of all pulsating stars, derives from the fact that stellar pulsations probe the interiors of stars, and thus they test directly our models of stellar interiors and stellar evolution. The relative value of stellar pulsations as such a probe depends on, among other factors, the number of pulsation modes simultaneously excited in a star, as each additional mode depends on and constrains the properties of the star in a different way. Judged by this criterion, the pulsations of the ZZ Ceti stars should be unusually valuable because all ZZ Ceti stars are multi-mode variables. (orig./WL)

On the polarization of Herbig Ae/Be star radiation

Energy Technology Data Exchange (ETDEWEB)

Petrova, N I; Shevchenko, V S

1987-08-01

Results of multicolor UBVRI polarimetry of 14 Herbig Ae/Be stars including 7 stars for which observations of polarization have been made for the first time are presented. 6 bright Herbig Ae/Be stars (As 441, AS 442, LK H..cap alpha..134, LK H..cap alpha..135, Lk H..cap alpha..169 and V517 Cyg) which belong to star formation region connected with IC 5070 show the polarization from 1 to 4.5. per cent with similar theta (approx. 180 deg) (basically of interstellar nature). The polarimetrical variability of BD+46 deg 3471, BD+65 deg 1637, HD 200775 and Lk H..cap alpha..234 is confirmed. Mechanismes of polarization in Herbig Ae/Be stars in circumstellar formations are discussed.

VARIABILITY IN HOT CARBON-DOMINATED ATMOSPHERE (HOT DQ) WHITE DWARFS: RAPID ROTATION?

Energy Technology Data Exchange (ETDEWEB)

Williams, Kurtis A.; Bierwagen, Michael [Department of Physics and Astrophysics, Texas A and M University-Commerce, P.O. Box 3011, Commerce, TX, 75429 (United States); Montgomery, M. H.; Winget, D. E.; Falcon, Ross E., E-mail: Kurtis.Williams@tamuc.edu [Department of Astronomy, University of Texas, 1 University Station C1400, Austin, TX, 78712 (United States)

2016-01-20

Hot white dwarfs (WDs) with carbon-dominated atmospheres (hot DQs) are a cryptic class of WDs. In addition to their deficiency of hydrogen and helium, most of these stars are highly magnetic, and a large fraction vary in luminosity. This variability has been ascribed to nonradial pulsations, but increasing data call this explanation into question. We present studies of short-term variability in seven hot DQ WDs. Three (SDSS J1426+5752, SDSS J2200−0741, and SDSS J2348−0942) were known to be variable. Their photometric modulations are coherent over at least two years, and we find no evidence for variability at frequencies that are not harmonics. We present the first time-series photometry for three additional hot DQs (SDSS J0236−0734, SDSS J1402+3818, and SDSS J1615+4543); none are observed to vary, but the signal-to-noise is low. Finally, we present high speed photometry for SDSS J0005−1002, known to exhibit a 2.1-day photometric variation; we do not observe any short-term variability. Monoperiodicity is rare among pulsating WDs, so we contemplate whether the photometric variability is due to rotation rather than pulsations; similar hypotheses have been raised by other researchers. If the variability is due to rotation, then hot DQ WDs as a class contain many rapid rotators. Given the lack of companions to these stars, the origin of any fast rotation is unclear—both massive progenitor stars and double degenerate merger remnants are possibilities. We end with suggestions of future work that would best clarify the nature of these rare, intriguing objects.

Two Cepheid variables in the Fornax dwarf galaxy

Science.gov (United States)