WorldWideScience

Sample records for cataclysmic variable stars

  1. 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.

  2. The origin of the infrared light of cataclysmic variable stars

    International Nuclear Information System (INIS)

    Berriman, G.; Szkody, P.; Capps, R.W.

    1985-01-01

    This paper presents a model-independent overview of the origin of the near infrared (1-2 μm) light of a sample of 28 cataclysmic binary stars, largely dwarf novae in quiescence. The infrared light comes from the red dwarf that supplies matter to the white dwarf companion and the accretion disc around the white dwarf. The complex nature of the disc prevents near-infrared photometry from being a good probe of the red dwarfs, even in those systems where they are seen in the visual. All that can be found reliably is an upper limit to the proportion light that the red dwarfs supply, and consequently lower limits to the distances to the systems. The infrared light of the discs comes from opaque material and from the optically thin gas that gives rise to the visual and UV emission lines. (author)

  3. White Dwarfs in Cataclysmic Variable Stars: Surface Temperatures and Evolution

    Directory of Open Access Journals (Sweden)

    Edward M. Sion

    2012-06-01

    Full Text Available A summary is presented of what is currently known about the surface temperatures of accreting white dwarfs (WDs detected in non-magnetic and magnetic cataclysmic variables (CVs based upon synthetic spectral analyses of far ultraviolet data. A special focus is placed on WD temperatures above and below the CV period gap as a function of the orbital period, Porb. The principal uncertainty of the temperatures for the CV WDs in the Teff - Porb distribution, besides the distance to the CV, is the mass of the WD. Only in eclipsing CV systems, an area of eclipsing binary studies, which was so central to Robert H. Koch’s career, is it possible to know CV WD masses with high precision.

  4. 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

  5. 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

  6. IUE observations of cataclysmic variable

    Science.gov (United States)

    Szkody, Paula

    1993-06-01

    Twenty two approved International Ultraviolet Explorer (IUE) programs were studied over a 14 year period. These programs are listed. The observations and subsequent analysis centered on cataclysmic variables (close binaries with a late main sequence star transferring material to a primary white dwarf via an accretion disk). The early studies highlighted the flux distribution of the accretion disk at outburst and quiescence, while later studies accomplished time-resolved observations throughout the orbital cycles, the study of the outflowing winds present at outburst, the study of the white dwarf in those systems with low accretion rate. There are 39 publications resulting from this work which are listed. These results include those for individual systems (Stepanian's star, Lanning 10, AM Her, MV Lyr, TV Col, VW Hyi, T Leo, IR Gem, TT Ari, Z Cam, BV Pup, IP Peg, PG1030+590, V1315 Aql, SW UMa, V426 Oph, WZ Sge, BY Cam, and U Gem) as well as review articles in journals and publications from reviews at meetings that summarize the impact of IUE on the study of accretion disks, white dwarfs, and hot spots resulting from stream impact as well as magnetic accretion columns.

  7. Cataclysmic variables observed with INTEGRAL

    Czech Academy of Sciences Publication Activity Database

    Šimon, Vojtěch; Hudec, René; Münz, Filip; Štrobl, Jan

    2006-01-01

    Roč. 6, č. 1 (2006), s. 149-154 ISSN 1009-9271 R&D Projects: GA ČR GA205/05/2167 Institutional research plan: CEZ:AV0Z10030501 Keywords : cataclysmic variables * intermediate polars * X-rays Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 0.746, year: 2006

  8. Non-radial oscillations of rotating stars and their relevance to the short-period oscillations of cataclysmic variables

    International Nuclear Information System (INIS)

    Papaloizou, J.; Pringle, J.E.

    1978-01-01

    The usual hypothesis, that the short-period coherent oscillations seen in cataclysmic variables are attributable to g modes in a slowly rotating white dwarf, is considered. It is shown that this hypothesis is untenable for three main reasons: (i) the observed periods are too short for reasonable white dwarf models, (ii) the observed variability of the oscillations is too rapid and (iii) the expected rotation of the white dwarf, due to accretion, invalidates the slow rotation assumption on which standard g-mode theory is based. The low-frequency spectrum of a rotating pulsating star is investigated taking the effects of rotation fully into account. In this case there are two sets of low-frequency modes, the g modes, and modes similar to Rossby waves in the Earth's atmosphere and oceans, which are designated r modes. Typical periods for such modes are 1/m times the rotation period of the white dwarfs outer layers (m is the aximuthal wavenumber). It is concluded that non-radial oscillations of rotating white dwarfs can account for the properties of the oscillations seen in dwarf novae. Application of these results to other systems is also discussed. (author)

  9. 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

  10. Study of the eclipses of cataclysmic variables

    International Nuclear Information System (INIS)

    Zhang, E.H.

    1986-01-01

    The cataclysmic variables (CV's) are all close binary stars in which a secondary star fills its Roche lobe and transfers mass to its white dwarf companion. The transferred mass forms an accretion disk or ring, around the white dwarf. Reliable determinations of the masses of the two-component stars, the distributions of temperature and brightness across the disk, and other parameters, are necessary to understand both the CV's and the accretion processes, but they are extremely difficult to measure. The best way to obtain this data is to observe eclipsing CV's. The author developed a computer program to synthesize light curves of eclipsing CV's using the most realistic model built so far to analyze the eclipses of CV's. A statistical method was developed to perform a complete error analysis of the results of the numerical studies. High-speed, multi-color photometry of three eclipsing CV's - HT Cas, U Gem, and AC Cnc - was obtained. Using the program to analyze the observed light curves, the author derived, for each system, the orbital inclination, the sizes, masses and temperature of the two component stars, and the temperature distribution across the disk

  11. Short-timescale variability in cataclysmic binaries

    International Nuclear Information System (INIS)

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

    1982-01-01

    Rapid variability, including flickering and pulsations, has been detected in cataclysmic binaries at optical and x-ray frequencies. In the case of the novalike variable TT Arietis, simultaneous observations reveal that the x-ray and optical flickering activity is strongly correlated, while short period pulsations are observed that occur at the same frequencies in both wavelength bands

  12. Evolution and Outbursts of Cataclysmic Variables

    Directory of Open Access Journals (Sweden)

    S.-B. Qian

    2015-02-01

    Full Text Available Mass transfer and accretion are very important to understand the evolution and observational properties of cataclysmic variables (CVs. Due to the lack of an accretion disk, eclipsing profiles of polars are the best source to study the character of mass transfer in CVs. By analyzing long-term photometric variations in the eclipsing polar HU Aqr, the property of mass transfer and accretion are investigated. The correlation between the brightness state change and the variation of the ingress profile suggests that both the accretion hot spot and the accretion stream are produced instantaneously. The observations clearly show that it is the variation of mass transfer causing the brightness state changes that is a direct evidence of variable mass transfer in a CV. It is shown that it is the local dark-spot activity near the L1 point to cause the change of the mass transfer rather than the activity cycles of the cool secondary star. Our results suggest that the evolution of CVs is more complex than that predicted by the standard model and we should consider the effect of variable mass accretion in nova and dwarf nova outbursts.

  13. X-ray Ne/O Ratio in Cataclysmic Variables

    Science.gov (United States)

    Schlegel, Eric M.; Rana, V.; Singh, K.; Girish, V.; Barrett, P.

    2006-12-01

    The Ne/O ratio has recently become a topic of considerable debate given the difficulties and discrepancies in recent measures of the Ne abundance in the Sun. We describe the results of an analysis of the permitted branches of the X-ray triplet transitions of Ne and O using the available spectra from the Chandra X-ray Observatory's High Energy Transmission Grating observations of cataclysmic variables. We compare our results with those obtained from the Sun and nearby stars.

  14. Eclipses of cataclysmic variables. II. U Geminorum

    International Nuclear Information System (INIS)

    Zhang, E.H.; Robinson, E.L.

    1987-01-01

    U Gem is an eclipsing dwarf nova with an orbital period of 4 h 15 m. High-speed, multicolor photometric observations of U Gem in its quiescent state were obtained. A program was used that synthesizes the light curves of cataclysmic variables to derive the properties of U Gem from its eclipses. Using radial velocity curves published by Wade (1981) and by Stover (1981), it was found that i = 69.7 + or - 0.7 deg, M1 = 1.12 + or - 0.13 solar masses, and M2 = 0.53 + or - 0.06 solar mass. The radial temperature distribution across the accretion disk in U Gem shows that the disk is a hollow ring around the white dwarf with R(out) = 0.30 + or - 0.04 and R(in) = 0.12 + or - 0.05 a, where a is the separation of the two stars. The temperature of the ring is 4800 + or - 300 K. The model also reproduces the published infrared light curves and ultraviolet spectral distributions of U Gem. A mass transfer rate of 7.8 x 10 to the -10th solar mass/yr is derived. The structure of the ring around the white dwarf is consistent with the current theories of accretion disk instabilities in dwarf novae. 39 references

  15. Cataclysmic Variables as Supernova Ia Progenitors

    Directory of Open Access Journals (Sweden)

    Stella Kafka

    2012-06-01

    Full Text Available Although the identification of the progenitors of type Ia supernovae (SNeIa remains controversial, it is generally accepted that they originate from binary star systems in which at least one component is a carbon-oxygen white dwarf (WD; those systems are grouped under the wide umbrella of cataclysmic variables. Current theories for SNeIa progenitors hold that, either via Roche lobe overflow of the companion or via a wind, the WD accumulates hydrogen or helium rich material which is then burned to C and O onto the WD’s surface. However, the specifics of this scenario are far from being understood or defined, allowing for a wealth of theories fighting for attention and a dearth of observations to support them. I discuss the latest attempts to identify and study those controversial SNeIa progenitors. I also introduce the most promising progenitor in hand and I present observational diagnostics that can reveal more members of the category.

  16. CCD time-resolved photometry of faint cataclysmic variables. III

    Science.gov (United States)

    Howell, Steve B.; Szkody, Paula; Kreidl, Tobias J.; Mason, Keith O.; Puchnarewicz, E. M.

    1990-01-01

    CCD time-resolved photometry in V, B, and near-IR for 17 faint cataclysmic variables (CVs) is presented and analyzed. The data are obtained at Kitt Peak National Observatory, the Perkins reflector, Lowell Observatory, and the Observatorio del Roque de los Muchachos from April-June 1989. The degree of variability and periodicities for the CVs are examined. It is observed that the variability of most of the stars is consistent with CV class behavior. Orbital periods for five CVs are determined, and three potential eclipsing systems are detected.

  17. 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.)

  18. Very-high-energy gamma-ray observations of pulsar wind nebulae and cataclysmic variable stars with MAGIC and development of trigger systems for IACTs

    Science.gov (United States)

    Lopez-Coto, Ruben

    2015-07-01

    lowest possible energy threshold with the LSTs of CTA. Together with this work, the trigger of the MAGIC telescopes was improved. We have simulated, tested and commissioned a new concept of stereoscopic trigger. This new system, that uses the information of the position of the showers on each of the MAGIC cameras, is dubbed "Topo-trigger". The scientific fraction of the thesis deals with galactic sources observed with the MAGIC telescopes. In Part III, I talk about the analysis of the VHE γ-ray emission of Pulsar Wind Nebulae (PWNe): the discovery of VHE γ-ray emission from the puzzling PWN 3C 58, the likely remnant of the SN 1181 AD and the weakest PWN detected at VHE to date; the characterization of the VHE tail of the Crab nebula by observing it at the highest zenith angles; and the search for an additional inverse Compton component during the Crab nebula flares reported by Fermi-LAT in the synchrotron regime. Part IV is concerned with searches for VHE γ-ray emission of cataclysmic variable stars. I studied, on a multiwavelength context, the VHE γ-ray nature of the previously claimed pulsed γ-ray emission of the cataclysmic variable AE Aqr. I also performed observations of novae and a dwarf nova to pinpoint the ac- celeration mechanisms taking place in this kind of objects and to discover a putative hadronic component of the soft γ-ray emission. A conclusion chapter summarizes all the work performed and lists prospects related with the topics treated in this thesis.

  19. White dwarf models of supernovae and cataclysmic variables

    International Nuclear Information System (INIS)

    Nomoto, K.; Hashimoto, M.

    1986-01-01

    If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae and observations. We describe various types of evolution of accreting white dwarfs as a function of binary parameters (i.e,. composition, mass, and age of the white dwarf, its companion star, and mass accretion rate), and discuss the conditions for the precursors of exploding or collapsing white dwarfs, and their relevance to cataclysmic variables. Particular attention is given to helium star cataclysmics which might be the precursors of some Type I supernovae or ultrashort period x-ray binaries. Finally we present new evolutionary calculations using the updated nuclear reaction rates for the formation of O+Ne+Mg white dwarfs, and discuss the composition structure and their relevance to the model for neon novae. 61 refs., 14 figs

  20. White Dwarfs in Cataclysmic Variables: An Update

    Directory of Open Access Journals (Sweden)

    E. M. Sion

    2015-02-01

    Full Text Available In this review, we summarize what is currently known about the surface temperatures of accreting white dwarfs in nonmagnetic and magnetic cataclysmic variables (CVs based upon synthetic spectral analyses of far ultraviolet data. We focus only on white dwarf surface temperatures, since in the area of chemical abundances, rotation rates, WD masses and accretion rates, relatively little has changed since our last review, pending the results of a large HST GO programinvolving 48 CVs of different CV types. The surface temperature of the white dwarf in SS Cygni is re-examined in the light of its revised distance. We also discuss new HST spectra of the recurrent nova T Pyxidis as it transitioned into quiescence following its April 2011 nova outburst.

  1. Discovery of a new short-period, eclipsing cataclysmic variable

    Science.gov (United States)

    Downes, R. A.; Mateo, M.; Szkody, P.; Jenner, D. C.; Margon, B.

    1986-01-01

    Photometry and spectroscopy of a newly recognized 14th mag eclipsing cataclysmic variable, KPD 1911 + 1212 (= SVS 8130, V1315 Agl) are reported. The system exhibits deep (1.7 mag) eclipses with period 0.1397 day. The spectrum is that of a high-excitation old nova and shows dramatic variability of the emission line strengths through the eclipse. The profiles of the Balmer emission lines are also phase-dependent, with prominent absorption cores appearing briefly near the inferior conjunction of the emission line source. There is no direct evidence for the secondary. A preliminary determination of radial velocity variations at modest spectral resolution yields K = 132 + or - 26 km/s for the Balmer emission lines. A model is presented for the system consistent with current data, which implies a mass for the primary and secondary stars of 0.9 and 0.4 solar mass respectively and in inclination of i = 78 deg.

  2. Searching for nova shells around cataclysmic variables

    Science.gov (United States)

    Sahman, D. I.; Dhillon, V. S.; Knigge, C.; Marsh, T. R.

    2015-08-01

    We present the results of a search for nova shells around 101 cataclysmic variables (CVs), using H α images taken with the 4.2-m William Herschel Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric H α Survey of the Northern Galactic Plane (IPHAS). Both telescopes are located on La Palma. We concentrated our WHT search on nova-like variables, whilst our IPHAS search covered all CVs in the IPHAS footprint. We found one shell out of the 24 nova-like variables we examined. The newly discovered shell is around V1315 Aql and has a radius of ˜2.5 arcmin, indicative of a nova eruption approximately 120 yr ago. This result is consistent with the idea that the high mass-transfer rate exhibited by nova-like variables is due to enhanced irradiation of the secondary by the hot white dwarf following a recent nova eruption. The implications of our observations for the lifetime of the nova-like variable phase are discussed. We also examined four asynchronous polars, but found no new shells around any of them, so we are unable to confirm that a recent nova eruption is the cause of the asynchronicity in the white dwarf spin. We find tentative evidence of a faint shell around the dwarf nova V1363 Cyg. In addition, we find evidence for a light echo around the nova V2275 Cyg, which erupted in 2001, indicative of an earlier nova eruption ˜300 yr ago, making V2275 Cyg a possible recurrent nova.

  3. Observing campaign on 17 cataclysmic variables

    Science.gov (United States)

    Waagen, Elizabeth O.

    2015-07-01

    Roque Ruiz-Carmona (Ph.D. candidate, Institute of Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen, The Netherlands) has requested AAVSO assistance with his campaign to observe 17 cataclysmic variables (CVs) with the William Herschel Telescope (WHT) next week. In order for WHT to observe each of the targets safely and to maximize the science value of the observations obtained, it is essential to know whether they are in outburst or quiescence. To this end, the PI has requested our observers to obtain an image of each of the targets so he may analyze them. For this campaign, it is not necessary for observers to determine and submit a magnitude estimate of each target, just to obtain an image and place it where the PI can access it. Any filter may be used, and a raw or reduced image of each target may be submitted. Only one image per observer per target should be submitted. Please do not submit multiple images of any target. Timing is very important because the PI has to decide whether to exclude any target(s) 24 hours in advance of the WHT observations. Thus, the images must be taken and posted within a certain window. Links to finder charts as well as reporting instructions and other information may be found in the full Alert Notice.

  4. IY UMa - The Eclipsing Cataclysmic Star

    Science.gov (United States)

    Shugarov, S.; Khruzina, T.; Katysheva, N.

    2007-05-01

    Multicolor photometric observations of SU UMa-type system IY UMa are presented. The observations were obtained during the 2004 superoutburst and in quiescence in 2005. The forms of eclipses in quiescence and during the 2004 superoutburst were analyzed. Some physical and geometrical characteristics of the component stars and accretion disk are estimated by using a ``hot line" model.

  5. Photometry of some more neglected bright cataclysmic variables and candidates

    Science.gov (United States)

    Bruch, Albert

    2018-01-01

    As part of an effort to better characterize bright cataclysmic variables (CVs) and related systems which have received little attention in the past light curves of four systems (V504 Cen, KT Eri, Ret 1 and CTCV 2056-3014) are analyzed. For some of these stars no time resolved photometry has been published previously. While flickering is observed in all systems except Ret 1, it is particularly strong in V504 Cen and CTCV 2056-3014. In the latter star, a previously observed 15.4 m period, leading to its tentative classification as an intermediate polar, is probably spurious. Variations on time scales of hundredths of days observed in the pre-outburst light curve of the classical nova KT Eri continue after the outburst but appear not to be strictly periodic. Furthermore, the long term post-outburst light curve exhibits modulations with quasi-periods of quite different length. Thus, these variations cannot be due to aspect related variations in a system with a giant component similar to some recurrent novae. Instead, the system possibly exhibits variations with a period of 0.1952 d which may be orbital. However, any such conclusion still requires confirmation. The absence of flickering in Ret 1 indicates that the system probably does not contain an accretion disk. Instead, the observation of slow variations supports a previous suspicion of low amplitude variability with a period >12 h.

  6. Cycles in the cataclysmic variable V795 Herculis

    Czech Academy of Sciences Publication Activity Database

    Šimon, Vojtěch; Polášek, Cyril; Štrobl, Jan; Hudec, René; Blažek, Martin

    2012-01-01

    Roč. 540, April (2012), A15/1-A15/11 ISSN 0004-6361 R&D Projects: GA ČR GA205/08/1207 Institutional research plan: CEZ:AV0Z10030501 Keywords : novae * cataclysmic variables * accretion disks Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  7. The properties of cataclysmic variables in photometric Halpha surveys

    NARCIS (Netherlands)

    Witham, A.R.; Knigge, C.; Gänsicke, B.T.; Aungwerojwit, A.; Corradi, R.L.M.; Drew, J.E.; Greimel, R.; Groot, P.J.; Morales-Rueda, L.; Rodriguez-Flores, E.R.; Rodriguez-Gil, P.; Steeghs, D.

    2006-01-01

    We report on the properties of 71 known cataclysmic variables (CVs) in photometric Halpha emission-line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Halpha Survey of the northern galactic plane (IPHAS) will soon provide r',i' and narrow-band Halpha

  8. On the flickering of hot spots in cataclysmic variables

    International Nuclear Information System (INIS)

    James, J.F.

    1987-01-01

    A flickering point source inside a scattering cloud will have its higher flicker frequencies attenuated because of delays caused by multiple scattering of photons in the cloud. The effect of this on the flicker spectrum of a cataclysmic variable is considered. (author)

  9. Lessons learned from ESA INTEGRAL: cataclysmic variables and blazars

    Czech Academy of Sciences Publication Activity Database

    Hudec, René; Gális, R.; Kocka, Matúš

    2010-01-01

    Roč. 81, č. 1 (2010), s. 320-325 ISSN 0037-8720. [Multifrequency behaviour of high energy cosmic sources. Vulcano, 25.05.2009-30.05. 2009] Institutional research plan: CEZ:AV0Z10030501 Keywords : high-energy sources * cataclysmic variables * INTEGRAL Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  10. High-Speed Photo-Polarimetry of Magnetic Cataclysmic Variables

    Directory of Open Access Journals (Sweden)

    S. B. Potter

    2015-02-01

    Full Text Available I review recent highlights of the SAAO High-speed Photo-POlarimeter (HIPPO on the study of magnetic Cataclysmic Variables. Its high-speed capabilities are demonstrated with example observations made of the intermediate polar NY Lup and the polar IGRJ14536-5522.

  11. Theoretical statistics of zero-age cataclysmic variables

    International Nuclear Information System (INIS)

    Politano, M.J.

    1988-01-01

    The distribution of the white dwarf masses, the distribution of the mass ratios and the distribution of the orbital periods in cataclysmic variables which are forming at the present time are calculated. These systems are referred to as zero-age cataclysmic variables. The results show that 60% of the systems being formed contain helium white dwarfs and 40% contain carbon-oxygen white dwarfs. The mean dwarf mass in those systems containing helium white dwarfs is 0.34. The mean white dwarf mass in those systems containing carbon-oxygen white dwarfs is 0.75. The orbital period distribution identifies four main classes of zero-age cataclysmic variables: (1) short-period systems containing helium white dwarfs, (2) systems containing carbon-oxygen white dwarfs whose secondaries are convectively stable against rapid mass transfer to the white dwarf, (3) systems containing carbon-oxygen white dwarfs whose secondaries are radiatively stable against rapid mass transfer to the white dwarf and (4) long period systems with evolved secondaries. The white dwarf mass distribution in zero-age cataclysmic variables has direct application to the calculation of the frequency of outburst in classical novae as a function of the mass of the white dwarf. The method developed in this thesis to calculate the distributions of the orbital parameters in zero-age cataclysmic variables can be used to calculate theoretical statistics of any class of binary systems. This method provides a theoretical framework from which to investigate the statistical properties and the evolution of the orbital parameters of binary systems

  12. Atlas of time-resolved spectrophotometry of cataclysmic variables

    International Nuclear Information System (INIS)

    Honeycutt, R.K.; Schlegel, E.M.; Kaitchuck, R.H.; Ohio State Univ., Columbus)

    1987-01-01

    Whole-orbit, time-resolved spectrophotometry of 18 cataclysmic variables is reduced and displayed in a homogeneous fashion. Each set of digital data is binned into a phase-dependent gray-scale image which resembles a single-trailed photographic spectrogram. This technique permits convient comparison of phase-dependent spectral changes among the different systems. The approximate wavelength interval 4250-4950 A was observed at 2.5 A resolution. This interval contains the accretion disk emission lines of H-beta, H-gamma, He I 4471 A, and He II 4686 A. A brief commentary on the phenomena that can be seen in the image of each star is given. These effects include orbital motion, line-profile changes during eclipse, and s-waves. Several epochs of data on UX UMa are presented, displaying yearly changes in the spectrum. A series of outburst spectra of RX And are included, showing how phase-dependent spectra evolve during outburst. EX Hya spectra are displayed folded on both the 98 minute and the 67 minute photometric periods. In all, 23 spectral data sets are displayed and discussed for the 18 systems. 53 references

  13. Galactic population of cataclysmic variables in soft X-rays

    Science.gov (United States)

    Kushwaha, Ankur; Girish, V.

    We study the statistical properties and estimate the spatial density (ρ) as well as the luminosity function (φ) for magnetic Cataclysmic Variables (mCVs) detected in solar vicinity by XMM - Newton Observatory in 2-10 keV. A total no. of 98 CVs (26 IPs, 47 Polars and 25 unclassified mCVs) have been selected for the task. The preliminary results of the study are presented here.

  14. On the masses of the white dwarfs in cataclysmic variables

    International Nuclear Information System (INIS)

    Livio, M.; Soker, N.

    1984-01-01

    The question of the masses of the white dwarfs in cataclysmic binaries is examined. It is shown that selection effects can explain an overabundance of massive white dwarfs in novae but not in dwarf novae. It is proposed that the spiralling-in process in the common envelope favours the formation of more massive white dwarfs A number of simplified spiralling-in calculations are performed. The calculations demonstrate that the probability of coalescence of the secondary with the primary core, or secondary dissipation, is higher in the case of a giant envelope than in the case of a super giant envelope. Consequently, binaries with primary core masses greater than approx. 0.7 Msolar masses (and thus massive white dwarf remnants), have a better chance of surviving common envelope evolution and are therefore better candidates for the formation of cataclysmic variables. (author)

  15. Brown dwarfs in retrogradely precessing cataclysmic variables?

    Directory of Open Access Journals (Sweden)

    Martin E.L.

    2011-07-01

    Full Text Available We compare Smoothed Particle Hydrodynamic simulations of retrogradely precessing accretion disks that have a white dwarf primary and a main sequence secondary with observational data and with theory on retrograde precession via tidal torques like those by the Moon and the Sun on the Earth [1, 2]. Assuming the primary does not accrete much of the mass lost from the secondary, we identify the theoretical low mass star/brown dwarf boundary. We find no observational candidates in our study that could qualify as brown dwarfs.

  16. Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, A. S.; Palhares, M. S. [IP and D, Universidade do Vale do Paraíba, 12244-000, São José dos Campos, SP (Brazil); Rodrigues, C. V.; Cieslinski, D.; Jablonski, F. J. [Divisão de Astrofísica, Instituto Nacional de Pesquisas Espaciais, 12227-010, São José dos Campos, SP (Brazil); Silva, K. M. G. [Gemini Observatory, Casilla 603, La Serena (Chile); Almeida, L. A. [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05508-900, São Paulo, SP (Brazil); Rodríguez-Ardila, A., E-mail: alexandre@univap.br [Laboratório Nacional de Astrofísica LNA/MCTI, 37504-364, Itajubá MG (Brazil)

    2017-04-01

    The increasing number of synoptic surveys made by small robotic telescopes, such as the photometric Catalina Real-Time Transient Survey (CRTS), provides a unique opportunity to discover variable sources and improves the statistical samples of such classes of objects. Our goal is the discovery of magnetic Cataclysmic Variables (mCVs). These are rare objects that probe interesting accretion scenarios controlled by the white-dwarf magnetic field. In particular, improved statistics of mCVs would help to address open questions on their formation and evolution. We performed an optical spectroscopy survey to search for signatures of magnetic accretion in 45 variable objects selected mostly from the CRTS. In this sample, we found 32 CVs, 22 being mCV candidates, 13 of which were previously unreported as such. If the proposed classifications are confirmed, it would represent an increase of 4% in the number of known polars and 12% in the number of known IPs. A fraction of our initial sample was classified as extragalactic sources or other types of variable stars by the inspection of the identification spectra. Despite the inherent complexity in identifying a source as an mCV, variability-based selection, followed by spectroscopic snapshot observations, has proved to be an efficient strategy for their discoveries, being a relatively inexpensive approach in terms of telescope time.

  17. X-ray Emission Lines in Cataclysmic Variables

    Science.gov (United States)

    Schlegel, E. M.; Singh, K. P.; Rana, V.; Girish, V.; Barrett, P. E.

    2005-12-01

    We describe a complete spectroscopic archival study of the emission lines from cataclysmic variables as observed by the Chandra X-ray Observatory using the High Energy Transmission Grating. G-, R-, and the H/He-like ratios are used to infer temperatures and densities for the emitting plasmas. The G-ratio for Si XIII indicates a minimum electron temperature of 106 K for the observed CVs. The Fe XVII 17.10/17.05 {Å} and 17.10/16.77 {Å} line ratios for all of the CVs imply densities greater than 1014 cm-3 or photoexcitation. The R ratios imply values from 1011 to 1014-15 cm-3. We do not convincingly detect any radiation recombination features. Implications for the physics of CV accretion processes are briefly discussed. The research of EMS was partially supported by contract NAS-39073 from NASA to SAO for the Chandra X-ray Observatory.

  18. Cataclysmic Variables from SDSS. VII. The Seventh Year (2006)

    Science.gov (United States)

    Szkody, Paula; Anderson, Scott F.; Hayden, Michael; Kronberg, Martin; McGurk, Rosalie; Riecken, Thomas; Schmidt, Gary D.; West, Andrew A.; Gänsicke, Boris T.; Nebot Gomez-Moran, Ada; Schneider, Donald P.; Schreiber, Matthias R.; Schwope, Axel D.

    2009-04-01

    Coordinates, magnitudes, and spectra are presented for 39 cataclysmic variables (CVs) found in Sloan Digital Sky Survey (SDSS) spectra that were primarily obtained in 2006. Of these, 13 were CVs identified prior to the SDSS spectra (AK Cnc, GY Cnc, GO Com, ST LMi, NY Ser, MR Ser, QW Ser, EU UMa, IY UMa, HS1340+1524, RXJ1610.1+0352, Boo 1, Leo 5). Follow-up spectroscopic observations of seven systems (including one from year 2005 and another from year 2004) were obtained, resulting in estimates of the orbital periods for three objects. The new CVs include two candidates for high inclination, eclipsing systems, four new polars, and three systems whose spectra clearly reveal atmospheric absorption lines from the underlying white dwarf. Based on observations obtained with the Sloan Digital Sky Survey and with the Apache Point Observatory (APO) 3.5 m telescope, which are owned and operated by the Astrophysical Research Consortium (ARC).

  19. Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects

    Science.gov (United States)

    Oliveira, A. S.; Rodrigues, C. V.; Cieslinski, D.; Jablonski, F. J.; Silva, K. M. G.; Almeida, L. A.; Rodríguez-Ardila, A.; Palhares, M. S.

    2017-04-01

    The increasing number of synoptic surveys made by small robotic telescopes, such as the photometric Catalina Real-Time Transient Survey (CRTS), provides a unique opportunity to discover variable sources and improves the statistical samples of such classes of objects. Our goal is the discovery of magnetic Cataclysmic Variables (mCVs). These are rare objects that probe interesting accretion scenarios controlled by the white-dwarf magnetic field. In particular, improved statistics of mCVs would help to address open questions on their formation and evolution. We performed an optical spectroscopy survey to search for signatures of magnetic accretion in 45 variable objects selected mostly from the CRTS. In this sample, we found 32 CVs, 22 being mCV candidates, 13 of which were previously unreported as such. If the proposed classifications are confirmed, it would represent an increase of 4% in the number of known polars and 12% in the number of known IPs. A fraction of our initial sample was classified as extragalactic sources or other types of variable stars by the inspection of the identification spectra. Despite the inherent complexity in identifying a source as an mCV, variability-based selection, followed by spectroscopic snapshot observations, has proved to be an efficient strategy for their discoveries, being a relatively inexpensive approach in terms of telescope time. Based on observations obtained at the Observatório do Pico dos Dias/LNA, and 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).

  20. 20 Cataclysmic variables to be observed by William Herschel Telescope

    Science.gov (United States)

    Waagen, Elizabeth O.

    2016-05-01

    Roque Ruiz-Carmona (Ph.D. candidate, Institute of Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen, The Netherlands) has requested AAVSO assistance with his campaign to observe a set of 20 cataclysmic variables (CVs) with the William Herschel Telescope (WHT) at La Palma TONIGHT. This campaign is identical in format to the ones successfully carried out by the AAVSO on his behalf in 2015 (AAVSO Alert Notices 524 and 527). The full details of and instructions for this campaign are included here although the first of the two nights for which data are requested has passed. In order for WHT to observe each of the targets safely and to maximize the science value of the observations obtained, it is essential to know whether they are in outburst or quiescence. To this end, the PI has requested our observers to obtain one image of each target on each of TWO separate nights so he may analyze them to determine the final observing list for WHT. The images must be taken and posted within a certain window. Links to finder charts as well as reporting instructions and other information may be found in the full Alert Notice.

  1. 17 cataclysmic variables to be observed by William Herschel Telescope

    Science.gov (United States)

    Waagen, Elizabeth O.

    2015-08-01

    Roque Ruiz-Carmona (Ph.D. candidate, Institute of Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen, The Netherlands) has requested AAVSO assistance with his campaign to observe (a new set of) 17 cataclysmic variables (CVs) with the William Herschel Telescope (WHT) next week. This campaign is nearly identical in format to the one carried out by the AAVSO on his behalf in July (AAVSO Alert Notice 524). The success of that campaign prompted him to ask for the AAVSO's assistance in this new campaign. In order for WHT to observe each of the targets safely and to maximize the science value of the observations obtained, it is essential to know whether they are in outburst or quiescence. To this end, the PI has requested our observers to obtain one image of each target on each of TWO separate nights so he may analyze them to determine the final observing list for WHT. The images must be taken and posted within a certain window. Links to finder charts as well as reporting instructions and other information may be found in the full Alert Notice.

  2. 21 Cataclysmic variables to be observed by William Herschel Telescope

    Science.gov (United States)

    Waagen, Elizabeth O.

    2016-12-01

    Roque Ruiz-Carmona (Ph.D. candidate, Institute of Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen, The Netherlands) has requested AAVSO assistance with his campaign to observe a set of 21 cataclysmic variables (CVs) with the William Herschel Telescope (WHT) at La Palma on 2016 December 16. This campaign is essentially identical in format to the ones successfully carried out by the AAVSO on his behalf in 2015 and in May 2016 (AAVSO Alert Notices 524, 527, 543). Ruiz-Carmona writes: "As the end of my PhD is closer now, this is the second-to-last campaign monitoring CVs into outburst. As an update on my research, it seems that unexpectedly spiral density waves can only be detectable in high inclination systems and it seems that the luminosity of the disk in outburst outshines the spiral pattern for the rest of the system. This can also have deep implications: it can be that the spiral density waves are only an effect of the atmospheres of the disks and are therefore unrelated to transport of matter and angular momentum in the disks. In order to investigate this hypothesis, the sample of CVs I would like to monitor contains only eclipsing systems."[As before,] I just need to know if the targets are in outburst or not..." The PI has requested AAVSO observers to obtain one image of each target on each of TWO separate nights so he may analyze them to determine the final observing list for WHT. Links to finder charts as well as reporting instructions and other information may be found in the full Alert Notice.

  3. X-Ray Emission of Cataclysmic Variables Observed by Integral

    Czech Academy of Sciences Publication Activity Database

    Gális, R.; Eckert, D.; Paltani, S.; Münz, F.; Kocka, Matúš

    2009-01-01

    Roč. 18, 3-4 (2009), s. 321-326 ISSN 1392-0049 Grant - others:ESA(XE) ESA-PECS project No. 98023; VEGA(SK) 2/0078/10 Institutional research plan: CEZ:AV0Z10030501 Keywords : binaries starss * cataclysmic * X-rays Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.032, year: 2009

  4. Period changes of cataclysmic variables below the period gap: V2051 Oph, OY Car and Z Cha

    Science.gov (United States)

    Pilarčík, L.; Wolf, M.; Zasche, P.; Vraštil, J.

    2018-04-01

    We present our results of a long-term monitoring of cataclysmic variable stars (CVs). About 40 new eclipses were measured for the three southern SU UMa-type eclipsing CVs: V2051 Oph, OY Car and Z Cha. Based on the current O - C diagrams we confirmed earlier findings that V2051 Oph and OY Car present cyclic changes of their orbital periods lasting 25 and 29 years, respectively. In case of Z Cha we propose the light-time effect caused probably by a presence of the third component orbiting the eclipsing CV with the period of 43.5 years. The minimal mass of this companion results about 15 MJup.

  5. Interstellar absorption lines in high-resolution IUE spectra of cataclysmic variables

    International Nuclear Information System (INIS)

    Mauche, C.W.; Raymond, J.C.; Cordova, F.A.

    1988-01-01

    High-resolution ultraviolet spectra of five cataclysmic variables obtained with the IUE are used to investigate the character of the interstellar medium in the vicinity of the sun. These spectra reveal narrow absorption features of neutral and singly ionized interstellar species, and, in SS Cyg, narrow velocity-shifted absorption features of C IV, Si IV, and Si III. Using the column densities implied by the absorption features of the neutral and singly ionized species, values for the depletion of Si, Mg, Mn, and Fe from the gas phase of the interstellar medium in the vicinity of the sun are obtained. These hydrogen column densities are of particular importance in constraining the soft X-ray luminosity of cataclysmic variables because of the severe attenuation of the soft X-ray flux of cataclysmic variables by photoelectric absorption in the interstellar medium. In addition, using the column densities implied by the absorption features of C IV, Si IV, and Si III in the spectrum of SS Cyg, the existence of an expanding H II region of interstellar gas photoionized by he EUV and soft X-ray flux of this cataclysmic variable are inferred. 78 references

  6. Observed properties and long-term structure and evolution of white dwarfs in cataclysmic variables

    International Nuclear Information System (INIS)

    Sion, E.M.; Villanova Univ., PA)

    1985-01-01

    An attempt is made to explain the observed surface temperatures and luminosities of cataclysmic variable white dwarfs based on the cooling physics and time-averaged structure of the white dwarf in response to accretion. The evolutionary changes in core temperature and core luminosity as an accreting white dwarf evolves quasi-statically are compared with the cooling evolution of a nonaccreting, one solar mass, pure C-12 core. Then, the evolutionary behavior of the white dwarf envelope in mass and temperature, in response to long-term accretion, is used to predict temperatures and luminosities of white dwarfs during quiescent intervals between nova outbursts. It is shown that the observed luminosities and effective temperatures of the bare white dwarfs detected in some cataclysmic variables are the expected intrinsic values associated with classical nova thermonuclear outburst cycles. Two alternate interpretations of their observed surface temperatures and luminosities are assessed. 22 references

  7. Influence of the velocity gradient on the line formation in discs of cataclysmic variables

    Czech Academy of Sciences Publication Activity Database

    Korčáková, Daniela; Nagel, T.; Werner, K.; Suleimanov, V.; Votruba, Viktor

    2011-01-01

    Roč. 529, May (2011), A119/1-A119/8 ISSN 0004-6361 R&D Projects: GA ČR GP205/09/P476; GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : radiative transfer * numerical methods * cataclysmic variables Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.587, year: 2011

  8. The Golden Age of Cataclysmic Variables and Related Objects - II Concluding Address

    Directory of Open Access Journals (Sweden)

    F. Giovannelli

    2015-02-01

    Full Text Available Before to conclude officially this workshop — far from me the idea to attempt some concluding remarks already dealt at the meeting with various burning by Joseph Patterson, Mariko Kato, Dmitry Bisikalo, and Rene Hudec —, I would like to comment few highlights coming out from our fruitful week of discussions about The Golden Age of Cataclysmic Variables and Related Objects - II, without any pretension of completeness.

  9. Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers

    Science.gov (United States)

    Popham, Robert; Narayan, Ramesh

    1995-01-01

    We develop numerical models of accretions disks in cataclysmic variables (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically thick, and find that these solutions share several common features. The angular and radial velocities of the accreting material drop rapidly in a dynamical boundary layer, which has a radial width approximately 1%-3% of the white dwarf radius. The energy dissipated in this region diffuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width comparable to the disk thickness, approximately 5%-15% of the white dwarf radius. We examine the dependence of the boundary layer structure on the mass accretion rate, the white dwarf mass and rotation rate, and the viscosity parameter alpha. We delineate the boundary between optically thick and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with observations it may be possible to estimate alpha in CVs. We derive an expression for the total boundary layer luminosities as a function of the parameters and show that it agrees well with the luminosites of our numerical solutions. Finally, we calcuate simple blackbody continuum spectra of the boundary layer and disk emission for our solutions and compare these to soft X-ray, EUV, and He II emission-line observations of CVs. We show that, through such comparisons, it may be possible to determine the rotation rates of the accreting stars in CVs, and perhaps also the white dwarf masses and the accretion rates. The spectra are quite insensitive to alpha, so the uncertainty in this parameter does not affect such comparisons.

  10. New cataclysmic variables and other exotic binaries in the globular cluster 47 Tucanae*

    Science.gov (United States)

    Rivera Sandoval, L. E.; van den Berg, M.; Heinke, C. O.; Cohn, H. N.; Lugger, P. M.; Anderson, J.; Cool, A. M.; Edmonds, P. D.; Wijnands, R.; Ivanova, N.; Grindlay, J. E.

    2018-04-01

    We present 22 new (+3 confirmed) cataclysmic variables (CVs) in the non-core-collapsed globular cluster 47 Tucanae (47 Tuc). The total number of CVs in the cluster is now 43, the largest sample in any globular cluster so far. For the identifications we used near-ultraviolet (NUV) and optical images from the Hubble Space Telescope, in combination with X-ray results from the Chandra X-ray Observatory. This allowed us to build the deepest NUV CV luminosity function of the cluster to date. We found that the CVs in 47 Tuc are more concentrated towards the cluster centre than the main-sequence turn-off stars. We compared our results to the CV populations of the core-collapsed globular clusters NGC 6397 and NGC 6752. We found that 47 Tuc has fewer bright CVs per unit mass than those two other clusters. That suggests that dynamical interactions in core-collapsed clusters play a major role creating new CVs. In 47 Tuc, the CV population is probably dominated by primordial and old dynamically formed systems. We estimated that the CVs in 47 Tuc have total masses of ˜1.4 M⊙. We also found that the X-ray luminosity function of the CVs in the three clusters is bimodal. Additionally, we discuss a possible double degenerate system and an intriguing/unclassified object. Finally, we present four systems that could be millisecond pulsar companions given their X-ray and NUV/optical colours. For one of them we present very strong evidence for being an ablated companion. The other three could be CO or He white dwarfs.

  11. Unveiling the mysterious nature of the cataclysmic variable SDSS J153817.35+5123238.0

    Science.gov (United States)

    Pala, Anna

    2017-08-01

    Evolution of cataclysmic variables (CVs) is driven by angular momentum loss, which keeps mass loss from the donor star continually going, replenishing the disc with new higher-momentum material and maintaining, in this way, the accretion process. The angular momentum loss rate can be accurately constrained by measuring the white dwarf (WD) effective temperature (Teff), and provides one of the best available tests for the present model of the CV evolution. We conducted an HST/COS survey (ID 12870, PI Gaensicke) in which we measured Teff for 31 CV WDs. Our results are in good agreement with the theoretical prediction with one exception: SDSS J153817.35+5123238.0, a short period (93.1 min) CV which contains an anomalously hot WD. We argue that the system is either a very young CV ( 20Myr), or has been recently re-heated to 35000K. While the former hypothesis is statistically unlikely, the latter is most likely related to a nova eruption within the past few 1000 years or to additional mechanisms of angular momentum losses that are not account for by the present theory of CV evolution. To distinguish between these three scenarios, we need higher resolution UV observation to accurately measure the white dwarf mass, its effective temperature and photospheric abundances, along with a search for absorption features due to an ejected shell and their velocity. In this way we will constrain the WD age (from an improved mass measurement), its cooling rate (from this second temperature measurement) and we will also identify possible ashes and the expanding circumstellar gas shell expected in case of a recent nova explosion, shedding light on the mysterious nature of this system.

  12. Mind the Gap when Data Mining the Ritter-Kolb Cataclysmic Variable Catalogue

    Science.gov (United States)

    Sparks, Warren M.; Sion, Edward M.

    2017-01-01

    The cataclysmic variable (CV) binary consists of a white dwarf primary and a low-mass secondary which overflows its Roche lobe. The Ritter-Kolb catalogue (2003, A&A, 404, 301) is a collection (~1000) of CV binaries and related objects. We have mined this catalogue for CVs with unevolved secondaries whose mass ratio (secondary/primary) is known (~130). A plot of the secondary mass verses the log of the orbital period exhibits the well-known period gap at 2-3 hrs. In addition, this plot shows that the secondary masses just above the period gap are collectively much larger than those just below. The average of the first ten secondary masses above the period is 180% larger than the average below the gap.The disrupted magnetic braking hypothesis (Howell, Nelson, and Rappaport 2001, ApJ, 550, 897 [HNR]) predicts that when the secondary becomes fully convective, the magnetic braking, which has driven the secondary out of thermal equilibrium, stops. In adjusting to thermal equilibrium the secondary shrinks below its Roche lobe and no longer loses mass. The binary system ceases to appear as a CV until gravitational radiation loss brings the secondary back in contact with its Roche lobe. This scenario is at odds with the apparent secondary mass loss across the period gap. Either the secondary continues to lose mass while crossing the period gap or the secondary masses are miscalculated!Magnetic braking causes the secondary to expand or inflate larger than its single star counterpart. Any orbital parameter calculation which assumes a radius-mass relationship based on single main-sequence stars will overestimate the mass of the secondary. We can approximate this mass overestimation from calculations by HNR which take into account the thermal heating from magnetic braking. Using this approximation as a first-order correction to the secondary mass, we replot the deflated secondary mass versus the binary period. The deflated masses immediately above and below the period gap are

  13. Binary system parameters and the hibernation model of cataclysmic variables

    International Nuclear Information System (INIS)

    Livio, M.; Shara, M.M.; Space Telescope Science Institute, Baltimore, MD)

    1987-01-01

    The hibernation model, in which nova systems spend most of the time between eruptions in a state of low mass transfer rate, is examined. The binary systems more likely to undergo hibernation are determined. The predictions of the hibernation scenario are shown to be consistent with available observational data. It is shown how the hibernation scenario provides links between classical novae, dwarf novae, and novalike variables, all of which represent different stages in the cyclic evolution of the same systems. 72 references

  14. Evolution of cataclysmic binaries

    International Nuclear Information System (INIS)

    Paczynski, B.

    1981-01-01

    Cataclysmic binaries with short orbital periods have low mass secondary components. Their nuclear time scale is too long to be of evolutionary significance. Angular momentum loss from the binary drives the mass transfer between the two components. As long as the characteristic time scale is compared with the Kelvin-Helmholtz time scale of the mass losing secondary the star remains close to the main sequence, and the binary period decreases with time. If angular momentum loss is due to gravitational radiation then the mass transfer time scale becomes comparable to the Kelvin-Helmoltz time scale when the secondary's mass decreases to 0.12 Msub(sun), and the binary period is reduced to 80 minutes. Later, the mass losing secondary departs from the main sequence and gradually becomes degenerate. Now the orbital period increases with time. The observed lower limit to the orbital periods of hydrogen rich cataclysmic binaries implies that gravitational radiation is the main driving force for the evolution of those systems. It is shown that binaries emerging from a common envelope phase of evolution are well detached. They have to lose additional angular momentum to become semidetached cataclysmic variables. (author)

  15. Features of the mass transfer in magnetic cataclysmic variables with fast-rotating white dwarfs

    Directory of Open Access Journals (Sweden)

    Isakova Polina

    2014-01-01

    Full Text Available The flow structure in magnetic cataclysmic variables was investigated taking into account the effects of strong magnetic field and fast rotation of the white dwarf. We modeled the AE Aqr system as a unique object that has the rotation period of the white dwarf is about 1000 times shorter than the orbital period of the binary system. Observations show that in spite of fast rotation of the white dwarf some part of the stream from the inner Lagrange point comes into the Roche lobe region. We analyzed possible mechanisms preventing material to outflow from the system.

  16. Johannes Hevelius, Nova CK Vulpeculae (1670) and the ''hibernation'' model of cataclysmic variables

    International Nuclear Information System (INIS)

    Smak, J.

    1988-01-01

    I review the basic properties of cataclysmic variables and the thermonuclear runaway (TNR) theory of the outbursts of novae, including the ''hibernation'' model of cataclysmic variables proposed recently by Livio, Prialnik, Shara and others. The TNR theory, while remarkably successful is explaining (and predicting) a number of observational properties of novae, met also with some difficulties related to excessive mass-transfer rates in old novae and conflicting estimates of their space density. Both, the mass-transfer rates and space densities, are estimated from absolute magnitudes of novae as observed within decades before, or after their outbursts. Nova CK Vulpeculae (1670), the oldest recorded nova, was observed in 1670-1672 by Hevelius, whose observations - together with those by Anthelme and Cassini - were sufficiently numerous and accurate to permit a modern reconstruction of the light curve and its classification as a very slow nova. The nova is now 6 mag fainter than other old novae and this implies a very low mass-transfer rate (dM/dt)≤ 10 -12 M sun /year. CK Vul, together with a less extreme case of Nova WY Sge (1783), thus suggest that high luminosities and, hence, high accretion rates observed in more recent novae are maintained for no more than a century after outburst and that during millenia between outbursts novae ''hibernate'' at very low mass-transfer rates. 15 refs., 4 figs. (author)

  17. Historical Variable Star Catalogs

    OpenAIRE

    Pagnotta, Ashley; Graur, Or; Murray, Zachary; Kruk, Julia; Christie-Dervaux, Lucien; Chen, Dong Yi

    2015-01-01

    Slides from my talk during one of the Historical Astronomy Division sessions at AAS 225 in Seattle, WA (January 2015). A brief history of the variable star catalogs Henrietta Swan Leavitt and Cecilia Payne-Gaposchkin assembled at Harvard, and the update to them that some of our students at AMNH have done.(Figshare only previews the first few slides. Download the PDF to see all of them!)

  18. Newly discovered cataclysmic variables from the INT/WFC photometric Halpha survey of the northern Galactic plane

    NARCIS (Netherlands)

    Witham, A.R.; Knigge, C.; Aungwerojwit, A.; Drew, J.E.; Gänsicke, B.T.; Greimel, R.; Groot, P.J.; Roelofs, G.H.A.; Steeghs, D.; Woudt, P.A.

    2007-01-01

    We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric Halpha Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further follow-up observations. For the CV candidates IPHAS J013031.90+622132.4

  19. XMM-NEWTON AND OPTICAL OBSERVATIONS OF CATACLYSMIC VARIABLES FROM THE SLOAN DIGITAL SKY SURVEY

    International Nuclear Information System (INIS)

    Hilton, Eric J.; Szkody, Paula; Mukadam, Anjum; Henden, Arne; Dillon, William; Schmidt, Gary D.

    2009-01-01

    We report on XMM-Newton and optical results for six cataclysmic variables that were selected from Sloan Digital Sky Survey (SDSS) spectra because they showed strong He II emission lines, indicative of being candidates for containing white dwarfs with strong magnetic fields. While high X-ray background rates prevented optimum results, we are able to confirm SDSS J233325.92+152222.1 as an intermediate polar from its strong pulse signature at 21 minutes and its obscured hard X-ray spectrum. Ground-based circular polarization and photometric observations were also able to confirm SDSS J142256.31 - 022108.1 as a polar with a period near 4 hr. Photometry of SDSS J083751.00+383012.5 and SDSS J093214.82+495054.7 solidifies the orbital period of the former as 3.18 hr and confirms the latter as a high-inclination system with deep eclipses.

  20. The Golden Age of Cataclysmic Variables and Related Objects (Old and News

    Directory of Open Access Journals (Sweden)

    F. Giovannelli

    2015-02-01

    Full Text Available In this paper we review cataclysmic variables (CVs discussing several hot points about the renewing interest of today astrophysics about these sources. We will briefly discuss also about classical and recurrent novae, as well as the intriguing problem of progenitors of the Type Ia supernovae. This paper is an extended and updated version of the review by Giovannelli (2008. Because of limited length of the paper and our knowledge, this review does not pretend to be complete. However, we would like to demonstrate that the improvement on knowledge of the physics of our Universe is strictly related also with the multifrequency behaviour of CVs, which apparently in the recent past lost to have a leading position in modern astrophysics.

  1. Theoretical, numerical and experimental study of accretion shocks dynamics in magnetic cataclysmic variables

    International Nuclear Information System (INIS)

    Busschaert, Clotilde

    2013-01-01

    Magnetic cataclysmic variables are interacting binary Systems containing a highly magnetized white dwarf which accretes material from a companion. Material is led along magnetic field lines and falls onto the magnetic pole(s) supersonically forming an accretion column. As the material hits the surface, a reverse shock is formed and the shocked region is structured by the cooling effect of radiation processes. This work is a multidisciplinary study of the dynamics of the accretion column. Firstly, a numerical study of the accretion column structure at the astrophysical scale is presented. The observational consequences are discussed. This approach is completed by experiments using radiative flows generated by powerful lasers. The relevance of such experiments is based on the establishment of scaling laws. News scaling laws in the frame of radiative ideal or resistive MHD are exposed. The results of the sizing and the interpretation of the POLAR experimental campaign of 2012 on LULI2000 installation are presented. (author) [fr

  2. Machine learning from hard x-ray surveys: applications to magnetic cataclysmic variable studies

    Science.gov (United States)

    Scaringi, Simone

    2009-11-01

    Within this thesis are discussed two main topics of contemporary astrophysics. The first is that of machine learning algorithms for astronomy whilst the second is that of magnetic cataclysmic variables (mCVs). To begin, an overview is given of ISINA: INTEGRAL Scouce Identifiction Network Algorithm. This machine learning algorithm, using random forests, is applied to the IBIS/ISGRI data set in order to ease the production of unbiased future soft gamma-ray source catalogues. The feature extraction process on an initial candidate list is described together with feature merging. Three trainng and testing sets are created in order to deal with the diverse time-scales encountered when dealing with the gamma-ray sky: one dealing with faint persistent source recognition, one dealing with strong persistent sources and a final one dealing with transients. For the latter, a new transient detection technique is introduced and described: the transient matrix. Finally the performance of the network is assessed and discussed using the testing set and some illustrative source examples. ISINA is also compared to the more conventional approach of visual inspection. Next mCVs are discussed, and in particular the properties arising from a hard X-ray selected sample which has proven remarkably efficient in detecting intermediate polars and asynchronous polars, two of the rarest type of cataclysmic variables (CVs). This thesis focuses particularly on the link between hard X-ray properties and spin/orbital periods. To this end, a new sample of these objects is constructed by cross-corelating candidate sources detected in INTEGRAL/IBIS observations against catalogues of known CVs. Also included in the analysis are hard X-ray Observations from Swift/BAT and SUZAKU/HXD in order to make the study more complete. It is found that most hard X-ray detected mCVs have Pspin/Porb<0.1 above the period gap. In this respect, attention is given to the very low number of detected systems in any ban

  3. VizieR Online Data Catalog: Faint cataclysmic variables from SDSS (Woudt+, 2012)

    Science.gov (United States)

    Woudt, P. A.; Warner, B.; de Bude, D.; Macfarlane, S.; Schurch, M. P. E.; Zietsman, E.

    2013-01-01

    We present high-speed photometric observations of 20 faint cataclysmic variables (CVs) selected from the Sloan Digital Sky Survey (SDSS) and Catalina catalogues. Measurements are given of 15 new directly measured orbital periods, including four eclipsing dwarf novae (SDSS 0904+03, CSS 0826-00, CSS 1404-10 and CSS 1626-12), two new polars (CSS 0810+00 and CSS 1503-22) and two dwarf novae with superhumps in quiescence (CSS 0322+02 and CSS 0826-00). Whilst most of the dwarf novae presented here have periods below 2h, SDSS 0805+07 and SSS 0617-36 have relatively long orbital periods of 5.489 and 3.440h, respectively. The double-humped orbital modulations observed in SSS 0221-26, CSS 0345-01, CSS 1300+11 and CSS 1443-17 are typical of low-mass transfer rate dwarf novae. The white dwarf primary of SDSS 0919+08 is confirmed to have non-radial oscillations, and quasi-periodic oscillations were observed in the short-period dwarf nova CSS 1028-08 during outburst. We further report the detection of a new nova-like variable (SDSS 1519+06). The frequency distribution of orbital periods of CVs in the Catalina Real-time Transient Survey (CRTS) has a high peak near ~80min orbital period, independently confirming that found by Gansicke et al. (2009MNRAS.397.2170G) from SDSS sources. We also observe a marked correlation between the median in the orbital period distribution and the outburst class, in the sense that dwarf novae with a single observed outburst (over the 5-year baseline of the CRTS coverage) occur predominantly at shortest orbital period. (2 data files).

  4. NON-THERMAL EMISSION FROM CATACLYSMIC VARIABLES: IMPLICATIONS ON ASTROPARTICLE PHYSICS

    Directory of Open Access Journals (Sweden)

    Vojtech Šimon

    2013-12-01

    Full Text Available We review the lines of evidence that some cataclysmic variables (CVs are the sources of non-thermal radiation. It was really observed in some dwarf novae in outburst, a novalike CV in the high state, an intermediate polar, polars, and classical novae (CNe during outburst. The detection of this radiation suggests the presence of highly energetic particles in these CVs. The conditions for the observability of this emission depend on the state of activity, and the system parameters. We review the processes and conditions that lead to the production of this radiation in various spectral bands, from gamma-rays including TeV emission to radio. Synchrotron and cyclotron emissions suggest the presence of strong magnetic fields in CV. In some CVs, e.g. during some dwarf nova outbursts, the magnetic field generated in the accretion disk leads to the synchrotron jets radiating in radio. The propeller effect or a shock in the case of the magnetized white dwarf (WD can lead to a strong acceleration of the particles that produce gamma-ray emission via pi0 decay; even Cherenkov radiation is possible. In addition, a gamma-ray production via pi0 decay was observed in the ejecta of an outburst of a symbiotic CN. Nuclear reactions during thermonuclear runaway in the outer layer of the WD undergoing CN outburst lead to the production of radioactive isotopes; their decay is the source of gamma-ray emission. The production of accelerated particles in CVs often has episodic character with a very small duty cycle; this makes their detection and establishing the relation of the behavior in various bands difficult.

  5. Investigation of cataclysmic variables and related objects with the INTEGRAL satellite

    Czech Academy of Sciences Publication Activity Database

    Hudec, René; Šimon, Vojtěch; Münz, Filip; Štrobl, Jan

    -, č. 75 (2007), s. 21-23 ISSN 1801-5964. [Conference on Variable Stars Research /38./. Valašské Meziříčí, 17.11.2006-19.11.2006] R&D Projects: GA ČR GA205/05/2167 Institutional research plan: CEZ:AV0Z10030501 Keywords : circumstellar matter * satellites * X-rays binaries Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  6. Broad-band characteristics of seven new hard X-ray selected cataclysmic variables

    Science.gov (United States)

    Bernardini, F.; de Martino, D.; Mukai, K.; Russell, D. M.; Falanga, M.; Masetti, N.; Ferrigno, C.; Israel, G.

    2017-10-01

    We present timing and spectral analysis of a sample of seven hard X-ray selected cataclysmic variable candidates based on simultaneous X-ray and optical observations collected with XMM-Newton, complemented with Swift/BAT and INTEGRAL /IBIS hard X-ray data and ground-based optical photometry. For six sources, X-ray pulsations are detected for the first time in the range of ˜296-6098 s, identifying them as members of the magnetic class. Swift J0927.7-6945, Swift J0958.0-4208, Swift J1701.3-4304, Swift J2113.5+5422 and possibly PBC J0801.2-4625 are intermediate polars (IPs), while Swift J0706.8+0325 is a short (1.7 h) orbital period polar, the 11th hard X-ray-selected identified so far. X-ray orbital modulation is also observed in Swift J0927.7-6945 (5.2 h) and Swift J2113.5+5422 (4.1 h). Swift J1701.3-4304 is discovered as the longest orbital period (12.8 h) deep eclipsing IP. The spectra of the magnetic systems reveal optically thin multitemperature emission between 0.2 and 60 keV. Energy-dependent spin pulses and the orbital modulation in Swift J0927.7-6945 and Swift J2113.5+5422 are due to intervening local high-density absorbing material (NH ˜ 1022 - 23 cm-2). In Swift J0958.0-4208 and Swift J1701.3-4304, a soft X-ray blackbody (kT ˜ 50 and ˜80 eV) is detected, adding them to the growing group of `soft' IPs. White dwarf masses are determined in the range of ˜ 0.58-1.18 M⊙, indicating massive accreting primaries in five of them. Most sources accrete at rates lower than the expected secular value for their orbital period. Formerly proposed as a long-period (9.4 h) nova-like CV, Swift J0746.3-1608 shows peculiar spectrum and light curves suggesting either an atypical low-luminosity CV or a low-mass X-ray binary.

  7. Hubble Space Telescope Eclipse Observations of the Nova Like Cataclysmic Variable UX Ursae Majoris

    Science.gov (United States)

    Knigge, Christian; Long, Knox S.; Wade, Richard A.; Baptista, Raymundo; Horne, Keith; Hubeny, Ivan; Rutten, Rene G. M.

    1998-01-01

    We present and analyze Hubble Space Telescope observations of the eclipsing nova-like cataclysmic variable UX UMa obtained with the Faint Object Spectrograph. Two eclipses each were observed with the G160L grating (covering the ultraviolet waveband) in 1994 August and with the PRISM (covering the near-ultraviolet to near-infrared) in November of the same year. The system was about 50% brighter in November than in August, which, if due to a change in the accretion rate, indicates a fairly substantial increase in Mass accretion by about 50%. The eclipse light curves are qualitatively consistent with the gradual occultation of an accretion disk with a radially decreasing temperature distribution. The light curves also exhibit asymmetries about mideclipse that are likely due to a bright spot at the disk edge. Bright-spot spectra have been constructed by differencing the mean spectra observed at pre- and posteclipse orbital phases. These difference spectra contain ultraviolet absorption lines and show the Balmer jump in emission. This suggests that part of the bright spot may be optically thin in the continuum and vertically extended enough to veil the inner disk and/or the outflow from UX UMa in some spectral lines. Model disk spectra constructed as ensembles of stellar atmospheres provide poor descriptions of the observed posteclipse spectra, despite the fact that UX UMa's light should be dominated by the disk at this time. Suitably scaled single temperature model stellar atmospheres with T(sub eff) approximately equals 12,500-14,500 K actually provide a better match to both the ultraviolet and optical posteclipse spectra. Evidently, great care must be taken in attempts to derive accretion rates from comparisons of disk models to observations. One way to reconcile disk models with the observed posteclipse spectra is to postulate the presence of a significant amount of optically thin material in the system. Such an optically thin component might be associated with the

  8. Unsupervised classification of variable stars

    Science.gov (United States)

    Valenzuela, Lucas; Pichara, Karim

    2018-03-01

    During the past 10 years, a considerable amount of effort has been made to develop algorithms for automatic classification of variable stars. That has been primarily achieved by applying machine learning methods to photometric data sets where objects are represented as light curves. Classifiers require training sets to learn the underlying patterns that allow the separation among classes. Unfortunately, building training sets is an expensive process that demands a lot of human efforts. Every time data come from new surveys; the only available training instances are the ones that have a cross-match with previously labelled objects, consequently generating insufficient training sets compared with the large amounts of unlabelled sources. In this work, we present an algorithm that performs unsupervised classification of variable stars, relying only on the similarity among light curves. We tackle the unsupervised classification problem by proposing an untraditional approach. Instead of trying to match classes of stars with clusters found by a clustering algorithm, we propose a query-based method where astronomers can find groups of variable stars ranked by similarity. We also develop a fast similarity function specific for light curves, based on a novel data structure that allows scaling the search over the entire data set of unlabelled objects. Experiments show that our unsupervised model achieves high accuracy in the classification of different types of variable stars and that the proposed algorithm scales up to massive amounts of light curves.

  9. Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

    Science.gov (United States)

    Caballero, J. A.; Cornide, M.; de Castro, E.

    2010-03-01

    We look for high-amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS-3 Photometric V-band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5° centred on the bright star Alnilam (ɛ Ori) in the centre of the Orion Belt. We identify 32 highly variable stars, of which 16 had not been reported to vary before. They are mostly variable young stars and candidates (16) and background giants (8), but there are also field cataclysmic variables, contact binaries, and eclipsing binary candidates. Of the young stars, which typically are active Herbig Ae/Be and T Tauri stars with Hα emission and infrared flux excess, we discover four new variables and confirm the variability status of another two. Some of them belong to the well known σ Orionis cluster. Besides, six of the eight giants are new variables, and three are new periodic variables.

  10. 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).

  11. THE CHANDRA VARIABLE GUIDE STAR CATALOG

    International Nuclear Information System (INIS)

    Nichols, Joy S.; Lauer, Jennifer L.; Morgan, Douglas L.; Sundheim, Beth A.; Henden, Arne A.; Huenemoerder, David P.; Martin, Eric

    2010-01-01

    Variable stars have been identified among the optical-wavelength light curves of guide stars used for pointing control of the Chandra X-ray Observatory. We present a catalog of these variable stars along with their light curves and ancillary data. Variability was detected to a lower limit of 0.02 mag amplitude in the 4000-10000 A range using the photometrically stable Aspect Camera on board the Chandra spacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains 827 stars, of which 586 are classified as definitely variable and 241 are identified as possibly variable. Of the 586 definite variable stars, we believe 319 are new variable star identifications. Types of variables in the catalog include eclipsing binaries, pulsating stars, and rotating stars. The variability was detected during the course of normal verification of each Chandra pointing and results from analysis of over 75,000 guide star light curves from the Chandra mission. The VGUIDE catalog represents data from only about 9 years of the Chandra mission. Future releases of VGUIDE will include newly identified variable guide stars as the mission proceeds. An important advantage of the use of space data to identify and analyze variable stars is the relatively long observations that are available. The Chandra orbit allows for observations up to 2 days in length. Also, guide stars were often used multiple times for Chandra observations, so many of the stars in the VGUIDE catalog have multiple light curves available from various times in the mission. The catalog is presented as both online data associated with this paper and as a public Web interface. Light curves with data at the instrumental time resolution of about 2 s, overplotted with the data binned at 1 ks, can be viewed on the public Web interface and downloaded for further analysis. VGUIDE is a unique project using data collected during the mission that would otherwise be ignored. The stars available for use as Chandra guide stars are

  12. Rapid oscillations in cataclysmic variables. VI. Periodicities in erupting dwarf novae

    International Nuclear Information System (INIS)

    Patterson, J.

    1981-01-01

    We report an extensive study of the coherent oscillations observed in high-speed photometry of dwarf novae during eruption. The oscillations are in all cases singly periodic and sinusoidal to the limits of measurement. The detection of oscillations in 14 separate eruptions of AH Her and SY Cnc enables a general study of period variations. The stars trace out characteristic loops (''banana diagrams'') in the period-intensity plane. New detections are also reported for SS Cyg, EM Cyg, and HT Cas

  13. A Construction of an Automatic Observation System for Bright and Long Period Variable Stars

    Directory of Open Access Journals (Sweden)

    Joh-Na Yoon

    2006-06-01

    Full Text Available An automatic observation system has been constructed at Chungbuk National University for the purpose of monitoring the bright and long period variable stars effectively. We improved the control part of 40cm telescope of the LX 200 and developed an observing software ObsTool II so that the telescope, CCD camera and dome can be controlled in one software. ObsTool II is a COM (Common Object Module based software, which can be easily reprogrammed in case that a new telescope or CCD camera is installed. Because this system has an additional function in which the telescope can switch the variable, comparison, and check stars respectively as like a photoelectric observation, we can observe the variable star even if the CCD view field does not contain the comparison star with the variable star. In order to check the system stability a W UMa type variable V523 Cas and a magnetic cataclysmic variable TT Ari have been observed with the constructed system and the results have been discussed in context with the possibility of a further application of our automatical observation system.

  14. FUSE Observations of the Bright, Eclipsing Nova-like Cataclysmic Variable, UX UMa (FUSE 2000)

    Science.gov (United States)

    Long, Knox; Froning, Cynthia

    2004-01-01

    This was a project to study the disk and wind of the eclipsing nova-like variable UX UMa, in order to better define the wind geometry of the system, including the nature of the transition region between the disk photosphere and the supersonic wind. We proposed to use phase resolved spectroscopy of the system, taking advantage of the fact that UX UMa is an eclipsing system, to isolate different regions of the wind and to use a Monte Carlo radiative transfer code to simulate the spectra through the eclipse.

  15. X-ray observations of INTEGRAL discovered cataclysmic variable IGR J17195-4100

    Science.gov (United States)

    Girish, V.; Singh, K. P.

    2012-11-01

    We present the analysis of archival X-ray data obtained with the XMM-Newton and Suzaku for a new intermediate polar identified as a counterpart of an INTEGRAL discovered γ-ray source, IGR J17195-4100. We report a new period of 1053.7 ± 12.2 s in X-rays. A new binary orbital period of 3.52-0.80+1.43 h is strongly indicated in the power spectrum of the time series. An ephemeris of the new period proposed as the spin period of the system has also been obtained. The various peaks detected in the power spectrum suggest a probable disc-less accretion system. The soft X-rays (<3 keV) dominate the variability seen in the X-ray light curves. The spin modulation shows energy dependence suggesting the possibility of a variable partial covering accretion column. The averaged spectral data obtained with XMM-Newton European Photon Imaging Camera (EPIC) cameras show a multi-temperature spectrum with a soft excess. The latter can be attributed to the varying coverage of accretion curtains.

  16. The WFCAM multiwavelength Variable Star Catalog

    Science.gov (United States)

    Ferreira Lopes, C. E.; Dékány, I.; Catelan, M.; Cross, N. J. G.; Angeloni, R.; Leão, I. C.; De Medeiros, J. R.

    2015-01-01

    Context. Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for a time-domain exploration of the NIR sky. Aims: We perform a comprehensive search for stellar variability using the optical-NIR multiband photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars and of extending the current scarce inventory of accurate NIR light curves for a number of variable star classes. Methods: Standard data-mining methods were applied to extract and fine-tune time-series data from the WSA. We introduced new variability indices designed for multiband data with correlated sampling, and applied them for preselecting variable star candidates, i.e., light curves that are dominated by correlated variations, from noise-dominated ones. Preselection criteria were established by robust numerical tests for evaluating the response of variability indices to the colored noise characteristic of the data. We performed a period search using the string-length minimization method on an initial catalog of 6551 variable star candidates preselected by variability indices. Further frequency analysis was performed on positive candidates using three additional methods in combination, in order to cope with aliasing. Results: We find 275 periodic variable stars and an additional 44 objects with suspected variability with uncertain periods or apparently aperiodic variation. Only 44 of these objects had been previously known, including 11 RR Lyrae stars on the outskirts of the globular cluster M 3 (NGC 5272). We provide a preliminary classification of the new variable stars that have well-measured light curves, but the variability types of a large number of objects remain ambiguous. We classify most of the new variables as contact binary stars, but we also find several pulsating stars, among which

  17. The ESA Gaia Mission and Variable Stars

    Czech Academy of Sciences Publication Activity Database

    Hudec, René; Šimon, Vojtěch

    -, č. 75 (2007), s. 9-11 ISSN 1801-5964. [Conference on Variable Stars Research /38./. Valašské Meziříčí, 17.11.2006-19.11.2006] R&D Projects: GA ČR GA205/05/2167; GA AV ČR IAA3003206 Institutional research plan: CEZ:AV0Z10030501 Keywords : satellites * variable stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  18. Photometric Variability of the Be Star Population

    Energy Technology Data Exchange (ETDEWEB)

    Labadie-Bartz, Jonathan; Pepper, Joshua; McSwain, M. Virginia [Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015 (United States); Bjorkman, J. E.; Bjorkman, K. S. [Ritter Observatory, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft, Toledo, OH 43606-3390 (United States); Lund, Michael B.; Rodriguez, Joseph E.; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Stevens, Daniel J. [Department of Astronomy, The Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); James, David J. [Cerro Tololo Inter-American Observatory, Casilla 603 La Serena (Chile); Kuhn, Rudolf B. [Southern African Large Telescope, P.O. Box 9, Observatory 7935, Cape Town (South Africa); Siverd, Robert J. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States); Beatty, Thomas G. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)

    2017-06-01

    Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10 years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.

  19. 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.

  20. Recovery of 29 Second Oscillations in Hubble Space Telescope Eclipse Observations of the Cataclysmic Variable UX Ursae Majoris

    Science.gov (United States)

    Knigge, Christian; Drake, Nick; Long, Knox S.; Wade, Richard A.; Horne, Keith; Baptista, Raymundo

    1998-01-01

    Low-amplitude (approximately 0.5%) 29 s oscillations have been detected in Hubble Space Telescope Faint Object Spectrograph eclipse observations of the nova-like cataclysmic variable UX UMa. These are the same dwarf nova-type oscillations that were originally discovered in this system in 1972. The 29 s oscillations are seen in one pair of eclipse sequences obtained with the FOS/PRISM in 1994 November but not in a similar pair obtained with the FOS/GI60L grating in August of the same year. The oscillations in the PRISM data are sinusoidal to within the small observational errors and undergo an approximately - 360' phase shift during eclipses (i.e., one cycle is lost). The amplitudes are highest at pre-eclipse orbital phases and exhibit a rather gradual eclipse whose shape is roughly similar to, although perhaps slightly narrower than, LTX UMa's overall light curve in the PRISM bandpass (2000-8000 A). Spectra of the oscillations have been constructed from pre-, mid, and post-eclipse data segments of the November observations. The spectra obtained from the out-of-eclipse segments are extremely blue, and only lower limits can be placed on the temperature of the source that dominates the modulated flux at these orbital phases. Lower limits derived from blackbody (stellar atmosphere) model fits to these data are >or equal to 95,000 K (> or equal to 85,000 K); the corresponding upper limits on the projected area of this source are all less than 2% of the white dwarf (WD) surface area. By contrast, oscillation spectra derived from mid- eclipse data segments are much redder. Fits to these spectra yield temperature estimates in the range 20,000 K approximately greater T and T approximately less than 30,000 K for both blackbody and stellar atmosphere models and corresponding projected areas of a few percent of the WD surface area. These estimates are subject to revision if the modulated emission is optically thin. We suggest that the ultimate source of the oscillations is a

  1. IY Carinae - a Mira Type Variable Star

    Science.gov (United States)

    Williams, Peter

    2005-03-01

    Results of 18 years observation provide the previously lacking basic catalogue data on the Mira type variable star IY Carinae. A visual magnitude range of 10.1 to fainter then 15.0 and a mean period of 283.90 days are found. An epoch for determining dates of maximum brightness is JD 2447919±283.90 days

  2. 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.

  3. X-ray emission line spectroscopy of cataclysmic variables. II. Temperatures and densities from line ratios in the Chandra HETG band

    International Nuclear Information System (INIS)

    Schlegel, E. M.; Shipley, H. V.; Rana, V. R.; Barrett, P. E.; Singh, K. P.

    2014-01-01

    We summarize the results of a line-by-line fitting analysis of the available spectra obtained using the Chandra High-Energy Transmission Grating. We confirm the existence of broad ionization and electron temperature ranges and high number densities in cataclysmic variables (CVs) of all subtypes. Temperatures range from ∼0.4 keV to ∼5-10 keV or more with a broad range detected in any given CV. In other words, single-temperature models do not describe the line emission. Number densities also cover a broad range, from 10 12 to >10 16 cm –3 . We demonstrate that much of the plasma is in a nonequilibrium state; the Fe emission, however, may arise from plasma in the ionization equilibrium.

  4. Testing the Hibernation Model for Cataclysmic Variable Evolution with Very-Long Very-Well-Sampled Light Curves of Old Novae

    Science.gov (United States)

    Schaefer, Bradley E.

    2014-06-01

    The Hibernation Model for the evolution of cataclysmic variables predicts that old novae should be fading at a rate of order one-magnitude-per-century or so, with no mechanism for the accretion rate to significantly increase. This old prediction has been basically impossible to test due to the absence of very long term light curves where all the magnitudes have been placed onto a single consistent photometric system. However, in the past year, I have created very-long and very-well sampled light curves for old novae with the magnitudes fully corrected into the Johnson B & V system. I have these long light curves for Q Cyg (Nova Cyg 1876), V603 Aql (Nova Aql 1918), GK Per (Nova Per 1901), BT Mon (Nova Mon 1939), and QZ Aur (Nova Aur 1964) plus its orbital period change across its 1964 eruption. The comparison with the Hibernation prediction is mixed.

  5. 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

  6. The variable stars of NGC 1866

    Science.gov (United States)

    Welch, Douglas L.; Cote, Patrick; Fischer, Philippe; Mateo, Mario; Madore, Barry 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.

  7. The OmegaWhite survey for short-period variable stars - III: follow-up photometric and spectroscopic observations

    Science.gov (United States)

    Macfarlane, S. A.; Woudt, P. A.; Groot, P. J.; Ramsay, G.; Toma, R.; Motsoaledi, M.; Crause, L. A.; Gilbank, D. G.; O'Donoghue, D.; Potter, S. B.; Sickafoose, A. A.; van Gend, C.; Worters, H. L.

    2017-02-01

    We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey, a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0- and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find that many of these variables have spectra which are consistent with being δ Scuti-type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the `Bump Cepheid' phenomena in a δ Scuti star, with OW J175848.21-271653.7 showing a pronounced 22 per cent amplitude dip lasting 3 min during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.

  8. 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

  9. Precision Photometry of Long Period Variable Stars

    Science.gov (United States)

    Mais, D. E.; Bhatia, A.; Stencel, R. E.; Richards, D.

    2004-05-01

    Recently, evidence has been accumulating to suggest that Mira variables may go through flare up stages which result in brightening on the order of several tenths of a magnitude or more, and may last hours to days in length (Schaefer 1991, Maffei and Tosti 1995 and de Laverny 1998). Very little is known about these events, indeed it is not clear that these events are real. If they are real events, the spectroscopic changes, which occur during these flare-up episodes, remain relatively unexplored. This project was initiated in order to monitor a group of program stars of these classes in the V and R photometric bands in the hopes of "catching" some of these stars during these flare ups, thus offering confirmation to their reality and to be able to conduct spectral analysis of the flare-ups in real time and compare these spectra to the non-flare spectra. During the course of the past year, nearly 98 program stars have been monitored to address the potential flare up episodes. These include 25 M-type, 16-S type and 57 C-type Mira's. However, this more careful monitoring appears to not detect comparable behavior in similar stars near their minimum light, but rather exhibits a "Cepheid bump-like" phenomenon in several cases after minimum light, typically around phase 0.6-0.8 (cf. Melikian, 1999). Interpretation as an intermittent overtone pulsation is provided, and its effect on dust production discussed. We acknowledge support from the estate of William Herschel Womble, for the University of Denver astronomers participating in this effort.

  10. A survey for southern delta Scuti variable stars

    International Nuclear Information System (INIS)

    McInally, C.J.; Austin, R.R.D.

    1978-01-01

    Twenty-nine field stars have been tested photoelectrically for short-period variability. Eighteen of these stars have spectral types between A2 and F5 and are not Am stars; of these, six have been discovered to be variable and one is a suspected variable. HD 185969, with a period of 0.361 day, has the longest known period for a star of the delta Scuti type. The predominance of discovered variables with amplitudes close to the detection limit is suggestive of most stars in the instability strip being pulsators. (author)

  11. 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.

  12. Ground- and space-based study of two globular cluster cataclysmic variables: M22 CV1 and M5 V101

    Science.gov (United States)

    Hourihane, A. P.; Callanan, P. J.; Cool, A. M.; Reynolds, M. T.

    2011-06-01

    As a class of compact binaries with large binding energy, cataclysmic variables (CVs) formed through close encounters play an important role in the dynamical evolution of globular clusters. As part of a systematic search for CVs undergoing dwarf nova (DN) eruptions in globular clusters, our 2004 monitoring programme of M22 detected an outburst of the DN candidate CV1 during May. We implement the ISIS image subtraction routine to obtain a light curve for an outburst of CV1. We present the outburst light curve as well as Hubble Space Telescope/Wide-Field Planetary Camera 2 (WFPC2) photometry in the V, U and near-ultraviolet (nUV) bands and a Chandra/Advanced CCD Imaging Spectrometer (ACIS) spectrum of the object. Our results confirm the DN nature of the outburst and the CV status of the object. We also present the results of a ground-based study of another globular cluster CV, M5 V101 - including quiescent medium-resolution William Herschel Telescope (WHT)/Intermediate dispersion Spectrograph and Imaging System (ISIS) spectroscopy in the B and R bands, displaying prominent Balmer and He I emission, and R-band photometry.

  13. THE CLASSIFICATION OF KEPLER B-STAR VARIABLES

    International Nuclear Information System (INIS)

    McNamara, Bernard J.; Jackiewicz, Jason; McKeever, Jean

    2012-01-01

    The light curves of 252 B-star candidates in the Kepler database are analyzed in a similar fashion to that done by Balona et al. to further characterize B-star variability, increase the sample of variable B stars for future study, and to identify stars whose power spectra include particularly interesting features such as frequency groupings. Stars are classified as either constant light emitters, β Cep stars, slowly pulsating B stars (SPBs), hybrid pulsators, binaries or stars whose light curves are dominated by rotation (Bin/Rot), hot subdwarfs, or white dwarfs. One-hundred stars in our sample were found to be either light constants or to be variable at a level of less than 0.02 mmag. We increase the number of candidate B-star variables found in the Kepler database by Balona et al. in the following fashion: β Cep stars from 0 to 10, SPBs from eight to 54, hybrid pulsators from seven to 21, and Bin/Rot stars from 23 to 82. For comparison purposes, approximately 51 SPBs and six hybrids had been known prior to 2007. The number of β Cep stars known prior to 2004 was 93. A secondary result of this study is the identification of an additional 11 pulsating white dwarf candidates, four of which possess frequency groupings.

  14. Period Changes and Evolution in Pulsating Variable Stars

    Science.gov (United States)

    Neilson, H. R.; Percy, J. R.; Smith, H. A.

    2016-12-01

    We review ways in which observations of the changing periods of pulsating variable stars can be used to detect and directly measure their evolution. We briefly describe the two main techniques of analysis-(O-C) analysis and wavelet analysis - and results for pulsating variable star types which are reasonably periodic: type I and II Cepheids, RR Lyrae stars, beta Cephei stars, and Mira stars. We comment briefly on delta Scuti stars and pulsating white dwarfs. For some of these variable star types, observations agree approximately with the predictions of evolutionary models, but there still exist significant areas of disagreement that challenge future models of stellar evolution. There may be a need, for instance, to include processes such as rotation, mass loss, and magnetic fields. There may also be non-evolutionary processes which are contributing to the period changes.

  15. Time Resolved Spectroscopy of Cepheid Variable Stars

    Science.gov (United States)

    Hartman, Katherine; Beaton, Rachael L.; SDSS-IV APOGEE-2 Team

    2018-01-01

    Galactic Cepheid variable stars have been used for over a century as standard candles and as the first rung of the cosmic distance ladder, integral to the calculation of the Hubble constant. However, it is challenging to observe Cepheids within the Milky Way Galaxy because of extinction, and there are still uncertainties in the Cepheid period-luminosity relation (or Leavitt Law) that affect these important distance calculations. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has provided spectra for a large sample of Galactic Cepheids, but the standard chemical abundance pipeline (ASPCAP) processing is not well-suited to pulsational variables, preventing us from using them to study metallicity effect in the Leavitt Law with standard processing. Using a standalone version of the ASPCAP pipeline, we present an analysis of individual visit spectra from a test sample of nine APOGEE Cepheids, and we compare its output to the stars’ literature abundance values. Based on the results of this comparison, we will be able to improve the standard analysis and process the entirety of APOGEE’s Cepheid catalogue to improve its abundance measurements. The resulting abundance data will allow us to constrain the effect of metallicity on the Leavitt Law and thus allow for more accurate Cepheid distance measurements for the determination of the Hubble constant.

  16. Time dependence of the UV resonance lines in the cataclysmic variables SU UMa, RX And and 0623+71

    International Nuclear Information System (INIS)

    Woods, J.A.; Drew, J.E.; Verbunt, Frank

    1990-01-01

    We present IUE observations of the dwarf novae SU UMa and RX And, and of the nova-like variable 0623 + 71. At the time of observation, SU UMa and RX And were in outburst. All three systems show variability in the wind-formed UV resonance lines of N v λ 1240, Si IV λ 1397 and C IV λ 1549 on timescale of hours. The amplitude of variation is smallest in RX And and largest in 0623 + 71. There is evidence that the variations observed in SU UMa's UV spectrum repeat on the orbital period. Our observations of SU UMa also reveal variability in the continuum flux during the decline from outburst maximum that is much more marked in the UV than at optical wavelengths. (author)

  17. Modifying the Standard Disk Model for the Ultraviolet Spectral Analysis of Disk-dominated Cataclysmic Variables. I. The Novalikes MV Lyrae, BZ Camelopardalis, and V592 Cassiopeiae

    Science.gov (United States)

    Godon, Patrick; Sion, Edward M.; Balman, Şölen; Blair, William P.

    2017-09-01

    The standard disk is often inadequate to model disk-dominated cataclysmic variables (CVs) and generates a spectrum that is bluer than the observed UV spectra. X-ray observations of these systems reveal an optically thin boundary layer (BL) expected to appear as an inner hole in the disk. Consequently, we truncate the inner disk. However, instead of removing the inner disk, we impose the no-shear boundary condition at the truncation radius, thereby lowering the disk temperature and generating a spectrum that better fits the UV data. With our modified disk, we analyze the archival UV spectra of three novalikes that cannot be fitted with standard disks. For the VY Scl systems MV Lyr and BZ Cam, we fit a hot inflated white dwarf (WD) with a cold modified disk (\\dot{M} ˜ a few 10-9 M ⊙ yr-1). For V592 Cas, the slightly modified disk (\\dot{M}˜ 6× {10}-9 {M}⊙ {{yr}}-1) completely dominates the UV. These results are consistent with Swift X-ray observations of these systems, revealing BLs merged with ADAF-like flows and/or hot coronae, where the advection of energy is likely launching an outflow and heating the WD, thereby explaining the high WD temperature in VY Scl systems. This is further supported by the fact that the X-ray hardness ratio increases with the shallowness of the UV slope in a small CV sample we examine. Furthermore, for 105 disk-dominated systems, the International Ultraviolet Explorer spectra UV slope decreases in the same order as the ratio of the X-ray flux to optical/UV flux: from SU UMa’s, to U Gem’s, Z Cam’s, UX UMa’s, and VY Scl’s.

  18. Little Bear’s pulsating stars: Variable star census of UMi dSph Galaxy

    Directory of Open Access Journals (Sweden)

    Kinemuchi K.

    2017-01-01

    Full Text Available Recent observations and a photometric search for variable stars in the Ursa Minor dwarf spheroidal galaxy (UMi dSph are presented. Our observations were taken at Apache Point Observatory in 2014 and 2016 using the 0.5m ARCSAT telescope and the West Mountain Observatory (WMO 0.9m telescope of Brigham Young University in 2016. Previously known RR Lyrae stars in our field of view of the UMi dSph are identified, and we also catalog new variable star candidates. Tentative classifications are given for some of the new variable stars. We have conducted period searches with the data collected with the WMO telescope. Our ultimate goal is to create an updated catalog of variable stars in the UMi dSph and to compare the RR Lyrae stellar characteristics to other RR Lyrae stars found in the Local Group dSph galaxies.

  19. Luminous variable stars with naked eye: data reduction including extinction

    Science.gov (United States)

    Sigismondi, Costantino

    2014-05-01

    The observation of variable stars from urban contexts is hampered by city lights and field of view. Some bright stars like Betelgeuse and Antares are visible from the majority of cities, and during clear nights can be accurately estimated with the naked eye. The reference stars should be bright stars, not necessarily at the same altitude, including the atmospheric extinction in the data reduction. The software Stellarium 0.12.4 calculates well the standard atmospheric extinction with stars at least 10 degrees above the horizon. The accuracy of visual estimations is better than 0.1 magnitudes.

  20. 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

  1. Modelling of W UMa-type variable stars

    Directory of Open Access Journals (Sweden)

    P. L. Skelton

    2010-01-01

    Full Text Available W Ursae Majoris (W UMa-type variable stars are over-contact eclipsing binary stars. To understand how these systems form and evolve requires observations spanning many years, followed by detailed models of as many of them as possible. The All Sky Automated Survey (ASAS has an extensive database of these stars. Using the ASAS V band photometric data, models of W UMatype stars are being created to determine the parameters of these stars. This paper discusses the classification of eclipsing binary stars, the methods used to model them as well as the results of the modelling of ASAS 120036–3915.6, an over-contact eclipsing binary star that appears to be changing its period.

  2. White dwarfs in cataclysmic variables

    International Nuclear Information System (INIS)

    Sion, E.M.

    1987-01-01

    The physical properties and evolutionary state of the underlying white dwarfs in CVs are explored. Observations of 25 white dwarfs with effective temperature upper limits of 9000-75,000 K are discussed. Correlations between effective temperature, orbital period, accretion rate, and CV type with respect to the CV period gap are considered. Quasi-static and hydrodynamic evolutionary models are used to explain the surface temperature/luminosity distribution ratios. 42 references

  3. Discovering new variable stars at Key Stage 3

    Science.gov (United States)

    Chubb, Katy; Hood, Rosie; Wilson, Thomas; Holdship, Jonathan; Hutton, Sarah

    2017-05-01

    Details of the London pilot of the ‘Discovery Project’ are presented, where university-based astronomers were given the chance to pass on some real and applied knowledge of astronomy to a group of selected secondary school pupils. It was aimed at students in Key Stage 3 of their education, allowing them to be involved in real astronomical research at an early stage of their education, the chance to become the official discoverer of a new variable star, and to be listed in the International Variable Star Index database (The International Variable Star Index, Version 1.1, American Association of Variable Star Observers (AAVSO), 2016, http://aavso.org/vsx), all while learning and practising research-level skills. Future plans are discussed.

  4. Variable stars in Leo A : RR Lyrae stars, short-period cepheids, and implications for stellar content

    NARCIS (Netherlands)

    Dolphin, AE; Saha, A; Claver, J; Skillman, ED; Cole, AA; Gallagher, JS; Tolstoy, E; Dohm-Palmer, RC; Mateo, M

    We present the results of a search for short-period variable stars in Leo A. We have found 92 candidate variables, including eight candidate RR Lyrae stars. From the RR Lyrae stars, we measure a distance modulus of (m - M)(0) = 24.51 +/- 0.12, or 0.80 +/- 0.04 Mpc. This discovery of RR Lyrae stars

  5. Variable Stars in the LMC Globular Cluster NGC 1754

    Science.gov (United States)

    Kuehn, Charles A., III; Taylor, L.; Smith, H. A.; Catelan, M.; Pritzl, B. J.; De Lee, N.

    2006-12-01

    We have used BVI observations taken with the SMARTS 1.3m telescope and with the SOAR telescope to identify variable stars in the vicinity of the old LMC cluster NGC 1754. We present light curves and periods for the variables and classify the variables according to type. The probability that the RR Lyrae stars found in the neighborhood of NGC 1754 actually belong to the cluster is discussed. Unlike most globular clusters of the Milky Way halo, many of the old star clusters of the LMC have Oosterhoff intermediate properties. The Oosterhoff classification of field and cluster RR Lyrae stars near NGC 1754 is considered. We thank the NSF for partial support of this research.

  6. 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.

  7. 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.

  8. A Modern Update and Usage of Historical Variable Star Catalogs

    Science.gov (United States)

    Pagnotta, Ashley; Graur, Or; Murray, Zachary; Kruk, Julia; Christie-Dervaux, Lucien; Chen, Dong Yi

    2015-01-01

    One of the earliest modern variable star catalogs was constructed by Henrietta Swan Leavitt during her tenure at the Harvard College Observatory (HCO) in the early 1900s. Originally published in 1908, Leavitt's catalog listed 1777 variables in the Magellanic Clouds (MCs). The construction and analysis of this catalog allowed her to subsequently discover the Cepheid period-luminosity relationship, now known as the Leavitt Law. The MC variable star catalogs were updated and expanded by Cecilia Payne-Gaposchkin in 1966 and 1971. Although newer studies of the MC variables have been performed since then, the new information has not always been correlated with the old due to a lack of modern descriptors of the stars listed in the Harvard MC catalogs. We will discuss the history of MC variable star catalogs, especially those compiled using the HCO plates, as well as our modernized version of the Leavitt and Payne-Gaposchkin catalogs. Our modern catalog can be used in conjunction with the archival plates (primarily via the Digital Access to a Sky Century @ Harvard scanning project) to study the secular behavior of the MC variable stars over the past century.

  9. Synergies between exoplanet surveys and variable star research

    Directory of Open Access Journals (Sweden)

    Kovacs Geza

    2017-01-01

    Full Text Available With the discovery of the first transiting extrasolar planetary system back in 1999, a great number of projects started to hunt for other similar systems. Because the incidence rate of such systems was unknown and the length of the shallow transit events is only a few percent of the orbital period, the goal was to monitor continuously as many stars as possible for at least a period of a few months. Small aperture, large field of view automated telescope systems have been installed with a parallel development of new data reduction and analysis methods, leading to better than 1% per data point precision for thousands of stars. With the successful launch of the photometric satellites CoRoT and Kepler, the precision increased further by one-two orders of magnitude. Millions of stars have been analyzed and searched for transits. In the history of variable star astronomy this is the biggest undertaking so far, resulting in photometric time series inventories immensely valuable for the whole field. In this review we briefly discuss the methods of data analysis that were inspired by the main science driver of these surveys and highlight some of the most interesting variable star results that impact the field of variable star astronomy.

  10. Synergies between exoplanet surveys and variable star research

    Science.gov (United States)

    Kovacs, Geza

    2017-09-01

    With the discovery of the first transiting extrasolar planetary system back in 1999, a great number of projects started to hunt for other similar systems. Because the incidence rate of such systems was unknown and the length of the shallow transit events is only a few percent of the orbital period, the goal was to monitor continuously as many stars as possible for at least a period of a few months. Small aperture, large field of view automated telescope systems have been installed with a parallel development of new data reduction and analysis methods, leading to better than 1% per data point precision for thousands of stars. With the successful launch of the photometric satellites CoRoT and Kepler, the precision increased further by one-two orders of magnitude. Millions of stars have been analyzed and searched for transits. In the history of variable star astronomy this is the biggest undertaking so far, resulting in photometric time series inventories immensely valuable for the whole field. In this review we briefly discuss the methods of data analysis that were inspired by the main science driver of these surveys and highlight some of the most interesting variable star results that impact the field of variable star astronomy.

  11. 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.

  12. VARIABLE STARS IN THE GLOBULAR CLUSTER NGC 2808

    Energy Technology Data Exchange (ETDEWEB)

    Kunder, Andrea; Walker, Alistair R. [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile); Stetson, Peter B. [Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, Victoria, BC (Canada); Catelan, Marcio; Amigo, Pia, E-mail: akunder@ctio.noao.edu, E-mail: mcatelan@astro.puc.cl [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2013-02-01

    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 {approx}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){sub RR0} = 0.56 {+-} 0.01 d and

    {sub 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 Cortes, a mean distance modulus of (m - M){sub 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.

  13. 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.

  14. 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

  15. Rapid variability of the EXor star NY Ori

    Science.gov (United States)

    Lorenzetti, D.; Arkharov, A. A.; Efimova, N.; Giannini, T.; Antoniucci, S.; Di Paola, A.; Larionov, V. M.

    2016-03-01

    We report on a rapid brightness variability of the classical EXor star NY Ori observed with the AZT24 1m IR telescope (Campo Imperatore, Italy), as a part of our program EXORCISM (EXOR OptiCal and Infrared Systematic Monitoring - Antoniucci et al. 2013 PPVI; Lorenzetti et al. 2009 ApJ 693, 1056).

  16. Software Development for Asteroid and Variable Star Research

    Science.gov (United States)

    Sweckard, Teaghen; Clason, Timothy; Kenney, Jessica; Wuerker, Wolfgang; Palser, Sage; Giles, Tucker; Linder, Tyler; Sanchez, Richard

    2018-01-01

    The process of collecting and analyzing light curves from variable stars and asteroids is almost identical. In 2016 a collaboration was created to develop a simple fundamental way to study both asteroids and variable stars using methods that would allow the process to be repeated by middle school and high school students.Using robotic telescopes at Cerro Tololo (Chile), Yerkes Observatory (US), and Stone Edge Observatory (US) data were collected on RV Del and three asteroids. It was discovered that the only available software program which could be easily installed on lab computers was MPO Canopus. However, after six months it was determined that MPO Canopus was not an acceptable option because of the steep learning curve, lack of documentation and technical support.Therefore, the project decided that the best option was to design our own python based software. Using python and python libraries we developed code that can be used for photometry and can be easily changed to the user's needs. We accomplished this by meeting with our mentor astronomer, Tyler Linder, and in the beginning wrote two different programs, one for asteroids and one for variable stars. In the end, though, we chose to combine codes so that the program would be capable of performing photometry for both moving and static objects.The software performs differential photometry by comparing the magnitude of known reference stars to the object being studied. For asteroids, the image timestamps are used to obtain ephemeris of the asteroid from JPL Horizons automatically.

  17. An Undergraduate Research Experience on Studying Variable Stars

    Science.gov (United States)

    Amaral, A.; Percy, J. R.

    2016-06-01

    We describe and evaluate a summer undergraduate research project and experience by one of us (AA), under the supervision of the other (JP). The aim of the project was to sample current approaches to analyzing variable star data, and topics related to the study of Mira variable stars and their astrophysical importance. This project was done through the Summer Undergraduate Research Program (SURP) in astronomy at the University of Toronto. SURP allowed undergraduate students to explore and learn about many topics within astronomy and astrophysics, from instrumentation to cosmology. SURP introduced students to key skills which are essential for students hoping to pursue graduate studies in any scientific field. Variable stars proved to be an excellent topic for a research project. For beginners to independent research, it introduces key concepts in research such as critical thinking and problem solving, while illuminating previously learned topics in stellar physics. The focus of this summer project was to compare observations with structural and evolutionary models, including modelling the random walk behavior exhibited in the (O-C) diagrams of most Mira stars. We found that the random walk could be modelled by using random fluctuations of the period. This explanation agreed well with observations.

  18. Minimum period and the gap in periods of Cataclysmic binaries

    International Nuclear Information System (INIS)

    Paczynski, B.; Sienkiewicz, R.

    1983-01-01

    The 81 minute cutoff to the orbital periods of hydrogen-rich cataclysmic binaries is consistent with evolution of those systems being dominated by angular momentum losses due to gravitational radiation. Unfortunately, many uncertainties, mainly poorly known atmospheric opacities below 2000 K, make is physically impossible to verify the quadrupole formula for gravitational radiation by using the observed cutoff at 81 minutes. The upper boundary of the gap in orbital periods observed at about 3 hours is almost certainly due to enhanced angular momentum losses from cataclysmic binaries which have longer periods. The physical mechanism of those losses is not identified, but a possible importance of stellar winds is pointed out. The lower boundary of the gap may be explained with the oldest cataclysmic binaries, whose periods evolved past the minimum at 81 minutes and reached the value of 2 hours within about 12 x 10 9 years after the binary had formed. Those binaries should have secondary components of only 0.02 solar masses, and their periods could be used to estimate ages of the oldest cataclysmic stars, and presumably the age of Galaxy. An alternative explanation for the gap requires that binaries should be detached while crossing the gap. A possible mechanism for this phenomenon is discussed. It requires the secondary components to be about 0.2 solar masses in the binaries just below the gap

  19. The variable stars of the young LMC cluster NGC 2164

    Science.gov (United States)

    Welch, Douglas L.; Mateo, Mario; Olszewski, Edward W.; Fischer, Philippe; Takamiya, Marianne

    1993-01-01

    The present search of the LMC cluster NGC 2164 for variable stars has uncovered one new member classical Cepheid variable with 3.772-day period; attention is also given to photometry for a previously unknown field overtone Cepheid variable with 3.4626-day period, and the 10.6878-day period HV 12078, which may be a member of the young NGC 2156 cluster. The clear separation of fundamental and overtone pulsators in the period-luminosity-color relation of known LMC cluster Cepheids establishes that the NGC 2164 member is a true overtone.

  20. Luminous blue variables and the fates of very massive stars.

    Science.gov (United States)

    Smith, Nathan

    2017-10-28

    Luminous blue variables (LBVs) had long been considered massive stars in transition to the Wolf-Rayet (WR) phase, so their identification as progenitors of some peculiar supernovae (SNe) was surprising. More recently, environment statistics of LBVs show that most of them cannot be in transition to the WR phase after all, because LBVs are more isolated than allowed in this scenario. Additionally, the high-mass H shells around luminous SNe IIn require that some very massive stars above 40  M ⊙ die without shedding their H envelopes, and the precursor outbursts are a challenge for understanding the final burning sequences leading to core collapse. Recent evidence suggests a clear continuum in pre-SN mass loss from super-luminous SNe IIn, to regular SNe IIn, to SNe II-L and II-P, whereas most stripped-envelope SNe seem to arise from a separate channel of lower-mass binary stars rather than massive WR stars.This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'. © 2017 The Author(s).

  1. Long Period Variable Stars in Globular Cluster NGC 6553

    Science.gov (United States)

    Kager, Elisabeth

    2010-04-01

    Long period variable stars (LPVs) are red giants or supergiants that vary in brightness as they pulsate radially. Their periods range from months to several years, and amplitudes can be many magnitudes. Studying these pulsation properties of LPVs as a function of position on the giant branch helps to constrain models of stellar structure, evolution, and pulsation. Studying LPVs in environments with known metallicity, age, and distance allows us to control these variables; globular clusters are an excellent environment. This study targets the metal-rich ([Fe/H] = -0.2) bulge globular cluster NGC 6553 in which variables have not been studied very thoroughly. Over the past year, 49 nights worth of data have been taken with PROMPT 4, a motorized telescope positioned at Cerro Tololo, Chile. Images have been processed, combined, and photometered and the stars' (X,Y) positions and brightness values were determined. The variability indices of the magnitudes of the stars between nights were used to find LPVs and plot their brightness as a function of time. These light curves will be characterized for their amplitude, period, and regularity; these can be used to compare to LPVs in other clusters at the same/other metallicities. A color-magnitude diagram will be created onto which the LPVs' position can be plotted to understand how far they are up the red giant branch to get a better understanding of their evolutionary state.

  2. 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.)

  3. Astronomical Plate Archives and Amateur Variable Star Researchers

    Czech Academy of Sciences Publication Activity Database

    Hudec, René

    -, č. 75 (2007), s. 3-8 ISSN 1801-5964. [Conference on Variable Star s Research /38./. Valašské Meziříčí, 17.11.2006-19.11.2006] R&D Projects: GA AV ČR IAA3003206 Institutional research plan: CEZ:AV0Z10030501 Keywords : astronomical archives * astronomical plates Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  4. Clear-sky Forecasting for Variable Star Observers (Abstract)

    Science.gov (United States)

    Dempsey, F.

    2017-06-01

    (Abstract only) Many amateur astronomers seem to rely on computer model-generated weather forecasts for clear sky predictions and get frustrated by imperfect forecasts. It is worthwhile to consider the shortcomings of computer model forecasts and look at some resources to help the variable star observer plan for clear skies, whether for visual observers wanting to get an observation of a particular target star in long-term light curve programs, multi-hour observations of short-period pulsating variables or eclipsing binaries, or photometry. I discuss difficult-to-forecast factors including low clouds caused by local terrain and topographic effects, persistent low-level stratocumulus during the cold season, fog, post-cold front dry intrusions, pre-warm front waves of clouds, gradual sinking and clearing of cloud layers, jetstream-level cirrus, debris clouds persisting from upwind thunderstorms and distant thunderstorm complexes, large-scale blocking patterns, and other situations to hopefully help the variable star observer to make optimum use of limited time under clear skies.

  5. The variable star population in the globular cluster NGC 6934

    Science.gov (United States)

    Yepez, M. A.; Arellano Ferro, A.; Muneer, S.; Giridhar, Sunetra

    2018-04-01

    We report an analysis of new V and I CCD time-series photometry of the globular cluster NGC 6934. Through the Fourier decomposition of the RR Lyrae light curves the mean values of [Fe/H] and the distance of the cluster were estimated; we found: [Fe/H]UVES = - 1.48 ± 0.14 and d = 16.03 ± 0.42 kpc, and [Fe/H]UVES = - 1.43 ± 0.11 and d = 15.91 ± 0.39 kpc, from the calibrations of RRab and RRc stars respectively. Independent distance estimations from SX Phe and SR stars are also discussed. Individual absolute magnitudes, radii and masses are also reported for RR Lyrae stars. We found 12 new variables: 4 RRab, 3 SX Phe, 2 W Virginis (CW) and 3 semi-regular (SR). The inter-mode or "either-or" region in the instability strip is shared by the RRab and RRc stars. This characteristic, observed only in some OoI clusters and never seen in an OoII, is discussed in terms of mass distribution in the ZAHB.

  6. 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.

  7. Spectroscopic Follow-up of X-Ray Sources in the ChaMPlane Survey: Identification of a New Cataclysmic Variable

    NARCIS (Netherlands)

    Servillat, M.; Grindlay, J.; van den Berg, M.; Hong, J.; Zhao, P.; Allen, B.

    2012-01-01

    We present a multi-object optical spectroscopy follow-up study of X-ray sources in a field along the Galactic plane (l = 327fdg42, b = 2fdg26) which is part of the Chandra Multi-wavelength Plane survey (ChaMPlane). We obtained spectra for 46 stars, including 15 likely counterparts to X-ray sources,

  8. A package for the automated classification of periodic variable stars

    Science.gov (United States)

    Kim, Dae-Won; Bailer-Jones, Coryn A. L.

    2016-03-01

    We present a machine learning package for the classification of periodic variable stars. Our package is intended to be general: it can classify any single band optical light curve comprising at least a few tens of observations covering durations from weeks to years with arbitrary time sampling. We use light curves of periodic variable stars taken from OGLE and EROS-2 to train the model. To make our classifier relatively survey-independent, it is trained on 16 features extracted from the light curves (e.g., period, skewness, Fourier amplitude ratio). The model classifies light curves into one of seven superclasses - δ Scuti, RR Lyrae, Cepheid, Type II Cepheid, eclipsing binary, long-period variable, non-variable - as well as subclasses of these, such as ab, c, d, and e types for RR Lyraes. When trained to give only superclasses, our model achieves 0.98 for both recall and precision as measured on an independent validation dataset (on a scale of 0 to 1). When trained to give subclasses, it achieves 0.81 for both recall and precision. The majority of misclassifications of the subclass model is caused by confusion within a superclass rather than between superclasses. To assess classification performance of the subclass model, we applied it to the MACHO, LINEAR, and ASAS periodic variables, which gave recall/precision of 0.92/0.98, 0.89/0.96, and 0.84/0.88, respectively. We also applied the subclass model to Hipparcos periodic variable stars of many other variability types that do not exist in our training set, in order to examine how much those types degrade the classification performance of our target classes. In addition, we investigate how the performance varies with the number of data points and duration of observations. We find that recall and precision do not vary significantly if there are more than 80 data points and the duration is more than a few weeks. The classifier software of the subclass model is available (in Python) from the GitHub repository (http

  9. Preliminary results of variable star search using KMTNet data

    Science.gov (United States)

    Jeon, Young-Beom

    2017-09-01

    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.

  10. 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.

  11. Computing Cosmic Cataclysms

    Science.gov (United States)

    Centrella, Joan M.

    2010-01-01

    The final merger of two black holes releases a tremendous amount of energy, more than the combined light from all the stars in the visible universe. This energy is emitted in the form of gravitational waves, and observing these sources with gravitational wave detectors requires that we know the pattern or fingerprint of the radiation emitted. Since black hole mergers take place in regions of extreme gravitational fields, we need to solve Einstein's equations of general relativity on a computer in order to calculate these wave patterns. For more than 30 years, scientists have tried to compute these wave patterns. However, their computer codes have been plagued by problems that caused them to crash. This situation has changed dramatically in the past few years, with a series of amazing breakthroughs. This talk will take you on this quest for these gravitational wave patterns, showing how a spacetime is constructed on a computer to build a simulation laboratory for binary black hole mergers. We will focus on the recent advances that are revealing these waveforms, and the dramatic new potential for discoveries that arises when these sources will be observed.

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

    Science.gov (United States)

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

    2018-04-01

    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).

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

    Science.gov (United States)

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

    2017-05-01

    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).

  14. 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...

  15. 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.

  16. 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)

  17. Understanding Space Weather: The Sun as a Variable Star

    Science.gov (United States)

    Strong, Keith; Saba, Julia; Kucera, Therese

    2012-01-01

    The Sun is a complex system of systems and until recently, less than half of its surface was observable at any given time and then only from afar. New observational techniques and modeling capabilities are giving us a fresh perspective of the solar interior and how our Sun works as a variable star. This revolution in solar observations and modeling provides us with the exciting prospect of being able to use a vastly increased stream of solar data taken simultaneously from several different vantage points to produce more reliable and prompt space weather forecasts. Solar variations that cause identifiable space weather effects do not happen only on solar-cycle timescales from decades to centuries; there are also many shorter-term events that have their own unique space weather effects and a different set of challenges to understand and predict, such as flares, coronal mass ejections, and solar wind variations.

  18. Variable stars in Local Group Galaxies - II. Sculptor dSph

    Science.gov (United States)

    Martínez-Vázquez, C. E.; Stetson, P. B.; Monelli, M.; Bernard, E. J.; Fiorentino, G.; Gallart, C.; Bono, G.; Cassisi, S.; Dall'Ora, M.; Ferraro, I.; Iannicola, G.; Walker, A. R.

    2016-11-01

    We present the identification of 634 variable stars in the Milky Way dwarf spheroidal (dSph) satellite Sculptor based on archival ground-based optical observations spanning ˜24 yr and covering ˜2.5 deg2. We employed the same methodologies as the `Homogeneous Photometry' series published by Stetson. In particular, we have identified and characterized one of the largest (536) RR Lyrae samples so far in a Milky Way dSph satellite. We have also detected four Anomalous Cepheids, 23 SX Phoenicis stars, five eclipsing binaries, three field variable stars, three peculiar variable stars located above the horizontal branch - near to the locus of BL Herculis - that we are unable to classify properly. Additionally, we identify 37 long period variables plus 23 probable variable stars, for which the current data do not allow us to determine the period. We report positions and finding charts for all the variable stars, and basic properties (period, amplitude, mean magnitude) and light curves for 574 of them. We discuss the properties of the RR Lyrae stars in the Bailey diagram, which supports the coexistence of subpopulations with different chemical compositions. We estimate the mean mass of Anomalous Cepheids (˜1.5 M⊙) and SX Phoenicis stars (˜1 M⊙). We discuss in detail the nature of the former. The connections between the properties of the different families of variable stars are discussed in the context of the star formation history of the Sculptor dSph galaxy.

  19. The Bulgarian Contribution to the Study of variable stars on observational data from the Kepler mission

    Science.gov (United States)

    Kjurkchieva, D. P.; Dimitrov, D. P.; Radeva, V. S.; Vasileva, D. L.; Atanasova, T. V.; Stateva, I. V.; Petrov, N. I.; Iliev, I. Kh.

    2018-02-01

    This review paper presents the results of investigations of variable stars obtained by Bulgarian astronomers based on observations of Kepler mission. The main contributions are: determination of orbits and global parameters of more than 100 binary stars; creation of the largest catalog of eccentric stars; identification of sixty new binaries with eccentricity over 0.5; discovery of 19 heartbeat stars; detailed investigation of the spot and flare activity of several binary stars; asteroseismic study of three pulsating stars; detection of deep transits of WD 1145+017 due to its disentangling planet system. The paper illustrates not only scientific significance but also educational and social impact of the work on these tasks.

  20. Luminous and variable stars in M31 and M33. II. Luminous blue variables, candidate LBVs, Fe II emission line stars, and other supergiants

    International Nuclear Information System (INIS)

    Humphreys, Roberta M.; Davidson, Kris; Weis, Kerstin; Bomans, D. J.; Burggraf, Birgitta

    2014-01-01

    An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33.

  1. Detection of Variable Stars in the Open Cluster M11 Using Difference Image Analysis Pipeline

    Directory of Open Access Journals (Sweden)

    Chung-Uk Lee

    2010-12-01

    Full Text Available We developed a photometric pipeline to be used for a wide field survey. This pipeline employs the difference image analysis (DIA method appropriate for the photometry of star dense field such as the Galactic bulge. To verify the performance of pipeline, the observed dataset of the open cluster M11 was re-processed. One hundred seventy eight variable stars were newly discovered by analyzing the light curves of which photometric accuracy was improved through the DIA. The total number of variable stars in the M11 observation region is 335, including 157 variable stars discovered by previous studies. We present the catalogue and light curves for the 178 variable stars. This study shows that the photometric pipeline using the DIA is very useful in the detection of variable stars in a cluster.

  2. On the Variability of Blue Straggler Stars in the Globular Cluster M53

    Directory of Open Access Journals (Sweden)

    Soo-Chang Rey

    1998-06-01

    Full Text Available We present the results of a search for photometric variable blue straggler stars (BSSs in the globular cluster M53. Six of the 151 probable BSSs are identified as variable candidates based on the robust variable star detection technique of Welch & Stetson (1993. Most variable BSS candidates appear to occupy the instability strip in the color-magnitude diagram, and they appear to have visual light amplitudes of 0.2 mag - 0.3 mag. Further observations are required, however, to resolve the nature of variability between pulsating stars and eclipsing binaries for these variable BSS candidates.

  3. 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

  4. 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.

  5. Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

    OpenAIRE

    Caballero, Jose A.; Cornide, M.; de Castro, E.

    2010-01-01

    We look for high-amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS-3 Photometric V-band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5 deg centred on the bright star Alnilam (eps Ori) in the centre of the Orion Belt. We identify 32 highly-variable stars, of whic...

  6. Star Wreck

    CERN Document Server

    Kusenko, A; Tinyakov, Peter G; Tkachev, Igor I; Kusenko, Alexander; Shaposhnikov, Mikhail; Tkachev, Igor I.

    1998-01-01

    Electroweak models with low-energy supersymmetry breaking predict the existence of stable non-topological solitons, Q-balls, that can be produced in the early universe. The relic Q-balls can accumulate inside a neutron star and gradually absorb the baryons into the scalar condensate. This causes a slow reduction in the mass of the star. When the mass reaches a critical value, the neutron star becomes unstable and explodes. The cataclysmic destruction of the distant neutron stars may be the origin of the gamma-ray bursts.

  7. Infrared photometry of cataclysmic variables. II - Evidence for ellipsoidal variations in CW MoN, X Leo, IP Peg, and AF CaM

    Science.gov (United States)

    Szkody, P.; Mateo, M.

    1986-08-01

    Broadband H or K light curves of the dwarf novae CM Mon, X Leo, IP Peg, and AF Cam reveal variations that can be attributed to ellipsoidal modulation of the secondaries in these systems. The present data imply orbital periods of 4.23 + or - 0.01 hr for CW Mon and 5.0 + or - 0.1 hr for X Leo. The high-amplitude ellipsoidal modulation of the secondary of CW Mon implies a large orbital inclination. The interpretation of the low-amplitude variability seen in X Leo is complicated by details in its light curve and a recent determination of its orbital period by Shafter and Harkness (1986) which differs significantly from the period inferred from the present observations. The light variations of the eclipsing system IP Peg are interpreted as showing a 0.2 mag ellipsoidal variation from the secondary superposed on a deep eclipse of the IR light of the white dwarf and hotspot. AF Cam shows marginal evidence for a low-amplitude variation implying a very short orbital period of 76 min. IR colors of SS Aur, AH Eri, and IR Gem as well as the above four objects are used to place limits on the properties of the secondaries and the distances to these systems.

  8. 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.

  9. Exploring the SDSS Dataset with Linked Scatter Plots: I. EMP, CEMP, and CV Stars

    Science.gov (United States)

    Carbon, Duane F.; Henze, Christopher; Nelson, Bron C.

    2017-01-01

    We present the results of a search for EMP, CEMP, and cataclysmic variable stars using a new exploration tool based on linked scatter plots (LSPs). Our approach is especially designed to work with very large spectrum data sets such as the SDSS, LAMOST, RAVE, and Gaia data sets and can be applied to stellar, galaxy, and quasar spectra. As a demonstration, we conduct a search for EMP, CEMP, and cataclysmic variable stars in the SDSS DR10 data set. We first created a 3326-dimensional phase space containing nearly 2 billion measures of the strengths of over 1600 spectral features in 569,738 SDSS stars. These measures capture essentially all the stellar atomic and molecular species visible at the resolution of SDSS spectra. We show how LSPs can be used to quickly isolate and examine interesting portions of this phase space. To illustrate, we use LSPs coupled with cuts in selected portions of phase space to extract EMP stars, C-rich EMP stars, and CV stars. We present identifications for 59 previously unrecognized candidate EMP stars and 11 previously unrecognized candidate CEMP stars. We also call attention to 2 candidate He II emission CV stars found by the LSP approach that have not yet been discussed in the literature.

  10. Variable Stars in M13. II.The Red Variables and the Globular Cluster Period-Luminosity Relation

    Science.gov (United States)

    Osborn, W.; Layden, A.; Kopacki, G.; Smith, H.; Anderson, M.; Kelly, A.; McBride, K.; Pritzl, B.

    2017-06-01

    New CCD observations have been combined with archival data to investigate the nature of the red variables in the globular cluster M13. Mean magnitudes, colors and variation ranges on the UBVIC system have been determined for the 17 cataloged red variables. 15 of the stars are irregular or semi-regular variables that lie at the top of the red giant branch in the color-magnitude diagram. Two stars are not, including one with a well-defined period and a light curve shape indicating it is an ellipsoidal or eclipsing variable. All stars redder than (V-IC)0=1.38 mag vary, with the amplitudes being larger with increased stellar luminosity and with bluer filter passband. Searches of the data for periodicities yielded typical variability cycle times ranging from 30 d up to 92 d for the most luminous star. Several stars have evidence of multiple periods. The stars' period-luminosity diagram compared to those from microlensing survey data shows that most M13 red variables are overtone pulsators. Comparison with the diagrams for other globular clusters shows a correlation between red variable luminosity and cluster metallicity.

  11. 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 ...

  12. The variable mass loss of the AGB star

    NARCIS (Netherlands)

    Decin, L.K.E.; Hony, S.; de Koter, A.; Molenberghs, G.; Dehaes, S.; Markwick-Kemper, F.

    2007-01-01

    Context: Low and intermediate mass stars lose a significant fraction of their mass through a dust-driven wind during the Asymptotic Giant Branch (AGB) phase. Recent studies show that winds from late-type stars are far from being smooth. Mass-loss variations occur on different time scales, from years

  13. 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...

  14. The nucleus of Abell 35 - A cataclysmic binary?

    Science.gov (United States)

    Acker, A.; Jasniewicz, G.

    1990-11-01

    Simultaneous photometric and spectroscopic observations of the visible central star BD - 22 deg 3467 of the large planetary nebula Abell 35 are reported. This fast rotating star has a spectral type G8IV, and shows a double peaked emission line at H-alpha, varying with a period identical to the photometric one, equal to 0.7653 days. Both the maximum brightness of the system, and the amplitude of the light curves in UBV have decreased between 1986 and 1988. Observations are interpreted as the behavior of a cataclysmic binary, where one component is a Roche-lobe-filling subgiant star and the other a white dwarf surrounded by an accretion disk. The size of the system is about 4 solar radii, with i = 15 deg; this value is compatible with the radius of a subgiant star. The mass of this star is estimated to about 1.5 solar masses. The brightness decrease could be caused by erratic dark starspots, probably linked with chromospheric activity of the G star.

  15. Radiative Transfer Through Discs of Cataclysmic Variables

    Czech Academy of Sciences Publication Activity Database

    Korčáková, Daniela; Nagel, T.; Werner, K.; Suleimanov, V.; Votruba, Viktor

    2010-01-01

    Roč. 1273, - (2010), s. 350-353 ISSN 1551-7616. [European White Dwarf Workshop /17./. Tübingen, 16.08.2010-20.08.2010] R&D Projects: GA ČR GP205/09/P476 Institutional research plan: CEZ:AV0Z10030501 Keywords : radiative transfer * Doppler effect, * accretion disks Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  16. The Magnetospheric Boundary in Cataclysmic Variables

    Directory of Open Access Journals (Sweden)

    Hellier Coel

    2014-01-01

    During outbursts, when the accretion flow increases by orders of magnitude, the disk pushes the magnetosphere inwards, and appears to feed field lines over a much greater range of magnetic azimuth. The non-equilibrium outburst behaviour shows an even richer phenomenology than in quiescence, adding DNOs and QPOs into the mix.

  17. On the Photometric Variability of Very Sharp-lined Cool mCP Stars

    Science.gov (United States)

    Pyper, Diane M.; Adelman, Saul J.

    2017-10-01

    We investigate the photometric variability of very sharp-lined cool mCP stars from a list published in 1970 by Dr. George W. Preston who suggested that some belonged to the long-period tail of the period distribution. In this study, we discuss our Strömgren uvby observations obtained with the Four College Automated Photometric Telescope (FCAPT) at the Fairborn Observatory for 22 of the stars in Preston’s list. We improved the periods of 11 stars. Further, we discuss results from the literature concerning the light, magnetic, and spectrum variability of these stars. Eleven of the stars are found to have periods longer than 20 days, and all but one of these stars display variations in the u and v filters that cannot be explained by the simple oblique rotator theory. We discuss some possible causes of this behavior.

  18. Modernizing the Harvard Observatory Catalog of Variable Stars in the Magellanic Clouds

    Science.gov (United States)

    Murray, Zachary; Kruk, Julia; Christie-Dervaux, Lucien; Chen, Dong Yi; Graur, Or; Pagnotta, Ashley

    2015-01-01

    We have modernized the Harvard College Observatory's catalog of variable stars in the Magellanic Clouds, compiled by Henrietta Swan Leavitt in 1908 and expanded by Cecilia Payne-Gaposchkin in 1966 and 1971. This catalog was originally used by Leavitt in 1912 to formulate the period-luminosity relation for Cepheid variable stars, one of the most important rungs on the extragalactic distance ladder. Many of the stars were identified in current catalogs by only their Harvard Variable number, without coordinates or magnitudes. We have digitized the variable-star catalog and converted the coordinates of the 2,184 variable stars from the Harvard College Observatory's now-defunct planar-grid system to the spherical Equatorial coordinate system. Our modernized version of the catalog will allow for more efficient use of the Harvard archival plates currently being scanned by the Digital Access to a Sky Century @ Harvard (DASCH) project. The combination of DASCH and our catalog allows users to readily access more than a century's worth of data on the variable stars in the Magellanic Clouds, leading to such projects as studying the long-term evolution of variable stars.

  19. The Variability of Sunlike Stars on Decadal Timescales

    National Research Council Canada - National Science Library

    Radick, Richard R; Lockwood, G. W; Henry, G. W; Baliunas, S. L

    2004-01-01

    The authors have successfully combined photometric observations of about 30 sun-like stars from Mount Wilson, Lowell, and Fairborn Observatories to extend their joint time series from 12 to 17 years...

  20. 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

    stars. Three of these: MCC 527, HD 81032, and HD 160934, were identified as likely optical counterparts of X-ray sources 1ES 0829+15.9, 1ES 0920-13.6, 1ES 1737+61.2 seen in the Einstien's IPC slew survey (Elvis et al. 1992). Another star, HD 95559, has been detected as an extreme ultraviolet (EUV) source named ...

  1. 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

  2. About the new B- and A-type periodic variable stars

    Science.gov (United States)

    Mowlavi, Nami; Saesen, Sophie; Barblan, Fabio; Semaan, Thierry; Eyer, Laurent

    2015-08-01

    New periodic variable stars of type B and A were discovered in 2013 in the open cluster NGC 3766 (Mowlavi et al. 2013), in a region of the Hertzsprung-Rusell diagram on the main sequence, between delta-Scuti and Slowly Pulsating B stars, where no periodic star was expected to be found. The observational properties of the potentially new class of variability challenged model predictions of pulsating stars that were available at the time of their discovery, and triggered new theoretical developments in the field.Meanwhile, we obtained additional observational elements that shed new light on these new periodic variable stars. First, we analyzed photometric data of three other young clusters with ages between about 15 to about 70 million years, for which we had up to seven years of observations. The analysis reveals the presence of the new periodic B- and A-type stars in those clusters as well, with properties similar to those found in NGC 3766, but with also new features. Second, we took spectra of all new periodic variables found in NGC 3766, using Giraffe multi-fiber spectrometer mounted on the VLT. Those data enable a better characterization of the nature of those stars.We present in this contribution the results of those two new studies, and their impacts on our understanding of the new periodic stars.

  3. THE MASSIVE STAR POPULATION IN M101. III. SPECTRA AND PHOTOMETRY OF THE LUMINOUS AND VARIABLE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Grammer, Skyler H.; Humphreys, Roberta M. [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota , Minneapolis, MN 55455 (United States); Gerke, Jill, E-mail: grammer@astro.umn.edu, E-mail: roberta@umn.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

    2015-05-15

    We discuss moderate-resolution spectra, multicolor photometry, and light curves of 31 of the most luminous stars and variables in the giant spiral M101. The majority are intermediate A- to F-type supergiants. We present new photometry and light curves for three known “irregular blue variables,” V2, V4, and V9, and identify a new candidate. Their spectra and variability confirm that they are luminous blue variable (LBV) candidates and V9 may be in an LBV-like maximum light state or eruption.

  4. 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.)

  5. Theoretical velocity structure of long-period variable star photospheres

    International Nuclear Information System (INIS)

    Hill, S.J.; Willson, L.A.

    1979-01-01

    Numerical models for shock waves propagating through atmospheres of cool supergiant stars for a grid of masses and surface gravities have been calculated calculated, assuming spherical symmetry, isothermality, and a periodic piston boundary condition. The results of these models can be restated using parameters derived in Willson and Hill; the reparametrization allows the generalization of these results to arbitrary stellar masses and radii. Applying the theoretical generalization to a variety of observed properties of R Leonis and o Ceti allows the selection of a limited range of probable masses and radii for these stars: Mapprox. =0.8--l.5M/sub sun/,Rapprox. =l.3--2.0 x 10 13 cm for o Cet and M=l.8--4.0M/sub sun/, R=l.7--2.5 x 10 13 cm for R Leo. We conclude that both stars are pulsating in the fundamental mode, with a pulsation constant Qapprox. =Od1

  6. 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.

  7. The Nainital–Cape Survey: A Search for Variability in Ap and Am Stars

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... The Am stars HD 98851, HD 102480, HD 13079 and HD 113878 were discovered to exhibit Scuti type variability. Photometric variability was also discovered in HD 13038, for which the type of peculiarity and variability is not fully explained. The null results of this survey are also presented and discussed.

  8. Spectroscopic Variability of Supergiant Star HD14134, B3Ia

    Indian Academy of Sciences (India)

    Y. M. Maharramov

    2017-06-19

    Jun 19, 2017 ... Abstract. Profile variations in the Hα and Hβ lines in the spectra of the star HD14134 are investigated using observations carried out in 2013–2014 and 2016 with the 2-m telescope at the Shamakhy Astrophysical Obser- vatory. The absorption and emission components of the Hα line are found to disappear ...

  9. Optical and Infrared Variability of UX Ori-Type Stars

    Science.gov (United States)

    Rostopchina-Shakhovskaya, A.; Grinin, V.; Shenavrin, V.; Shakhovskoy, D.; Demidova, T.; Belan, S.

    2017-06-01

    Analyzing data of the long-term simultaneous NIR and optical photometry of five UX Ori type stars we estimate intrinsic NIR luminosity of their circumstellar disks in I, J, H bands. The H to J flux ratio for WW Vul, CQ Tau, RR Tau, UX Ori is consistent with 1500 K blackbody radiation, a typical temperature of dust sublimation. For the same stars except RR Tau, J to I flux ratio suggests much hotter source with T>2000 K, probably the inner dust-free disk. In case of RR Tau this value is close to 1500 K, implying sublimating dust as a main contributor in all three bands. The SED for BF Ori differs from the rest of objects, with flux density peaking in J band, probably due to an unresolved cool companion.

  10. Amplitude Variability in gamma Dor and delta Sct Stars Observed by Kepler

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, Joyce Ann [Los Alamos National Laboratory; Kosak, Mary Katherine [Los Alamos National Laboratory; Bradley, Paul Andrew [Los Alamos National Laboratory; Jackiewicz, Jason [New Mexico State University, Las Cruces, NM

    2015-08-17

    The NASA Kepler spacecraft data revealed a large number of new multimode nonradially pulsating gamma Dor and delta Sct variable stars. The Kepler high-precision long time-series photometry makes it possible to study amplitude variations of the frequencies, and recent literature on amplitude and frequency variations in nonradially pulsating variables is summarized. Several methods are applied to study amplitude variability in about a dozen gamma Doradus or delta Scuti candidate variable stars observed for several quarters as part of the Kepler Guest Observer program. The magnitude and timescale of the amplitude variations are discussed, along with the presence or absence of correlations between amplitude variations for different frequencies of a given star. Proposed causes of amplitude spectrum variability that will require further investigation are also discussed.

  11. Hβ line profile variability of seven southern Be stars

    International Nuclear Information System (INIS)

    Mennickent, R.E.

    1991-01-01

    The results of spectroscopic observations of six B0-B4e and one B7e stars at the Manuel Foster Observatory (Chile) during 1984-87 are reported. By means of photographic spectroscopy (20 A/mm), equivalent widths, peak separations and V/R ratios were obtained for a total of 106 Hβ and 7 Hγ line profiles. Emission episodes in Hβ were detected in 27 CMa and λ Pav, lasting at least 5 months and 18 days respectively. Significant variations in the equivalent width of the Hβ emission line W β in time scales of months were found in κ CMa, PP Car and QY Car

  12. Stellar Variability of the Exoplanet Hosting Star HD 63454

    OpenAIRE

    {Kane} S.~R.; {Dragomir} D.; {Ciardi} D.~R.; {Lee} J.-W.; {Lo Curto} G.; {Lovis} C.; {Naef} D.; {Mahadevan} S.; {Pilyavsky} G.; {Udry} S.; {Wang} X.; {Wright} J.

    2011-01-01

    Of the hundreds of exoplanets discovered using the radial velocity technique, many are orbiting close to their host stars with periods less than 10 days. One of these, HD 63454, is a young active K dwarf which hosts a Jovian planet in a 2.82 day period orbit. The planet has a 14% transit probability and a predicted transit depth of 1.2%. Here we provide a re-analysis of the radial velocity data to produce an accurate transit ephemeris. We further analyse 8 nights of time series data to search...

  13. 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.

  14. 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.

  15. 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.

  16. On the variability of the two brightest stars in the galactic cluster IC 2391

    Science.gov (United States)

    Waelkens, C.; Rufener, F.

    1983-04-01

    Short-period pulsations have been suspected for the two brightest stars of the galactic cluster IC 2391. New photometric data show that both stars are indeed variable, but on a longer time scale. For ο Velorum, a period of 2.779 days is found, and it is shown that the existing data are consistent with this period. For HR 3467, a period of 1.553 days is derived. None of these stars varied on a shorter time scale. Possible explanations for the observed variations are discussed.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kuehn, Charles A.; Smith, Horace A.; De Lee, Nathan [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Catelan, Marcio [Facultad de Fisica, Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Santiago (Chile); Pritzl, Barton J. [Department of Physics and Astronomy, University of Wisconsin Oskosh, Oshkosh, WI 54901 (United States); Borissova, Jura, E-mail: kuehn@physics.usyd.edu.au, E-mail: smith@pa.msu.edu, E-mail: nathan.delee@vanderbilt.edu, E-mail: mcatelan@astro.puc.cl, E-mail: pritzlb@uwosh.edu, E-mail: jura.borissova@uv.cl [Departamento de Fisica y Astronomia, Falcultad de Ciencias, Universidad de Valparaiso, Valparaiso (Chile)

    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.

  18. 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.

  19. 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.

  20. Stars

    CERN Document Server

    Hansen, Grace

    2017-01-01

    This title will cover how stars form, different types of stars, their lifecycle, and the most important star to us--the Sun! Aligned to Common Core Standards and correlated to state standards. Abdo Kids Jumbo is an imprint of Abdo Kids, a division of ABDO.

  1. AUTOMATIC CLASSIFICATION OF VARIABLE STARS IN CATALOGS WITH MISSING DATA

    International Nuclear Information System (INIS)

    Pichara, Karim; Protopapas, Pavlos

    2013-01-01

    We present an automatic classification method for astronomical catalogs with missing data. We use Bayesian networks and a probabilistic graphical model that allows us to perform inference to predict missing values given observed data and dependency relationships between variables. To learn a Bayesian network from incomplete data, we use an iterative algorithm that utilizes sampling methods and expectation maximization to estimate the distributions and probabilistic dependencies of variables from data with missing values. To test our model, we use three catalogs with missing data (SAGE, Two Micron All Sky Survey, and UBVI) and one complete catalog (MACHO). We examine how classification accuracy changes when information from missing data catalogs is included, how our method compares to traditional missing data approaches, and at what computational cost. Integrating these catalogs with missing data, we find that classification of variable objects improves by a few percent and by 15% for quasar detection while keeping the computational cost the same

  2. Spectroscopic Variability of Supergiant Star HD14134, B3Ia

    Indian Academy of Sciences (India)

    Y. M. Maharramov

    2017-06-19

    Jun 19, 2017 ... Orion, Astrophys. J., 150, 535. Pasok, A., Kolka, I. 1992, The Hα profile variations in the spectrum of HD225094, B3Ia, IBVS, 3804. Prinja R. K. et al. 1996, Variability in the optical wind lines of HD151804 (O9Iaf), Astron. Astrophys., 311,. 264. Rosendhal, J. D. 1973, A survey of Hα emission in early-type.

  3. Variable Stars and Stellar Populations in Andromeda XXVII. IV. An Off-centered, Disrupted Galaxy

    Science.gov (United States)

    Cusano, Felice; Garofalo, Alessia; Clementini, Gisella; Cignoni, Michele; Muraveva, Tatiana; Tessicini, Gianni; Testa, Vincenzo; Paris, Diego; Federici, Luciana; Marconi, Marcella; Ripepi, Vincenzo; Musella, Ilaria

    2017-12-01

    We present B and V time-series photometry of the M31 satellite galaxy Andromeda XXVII (And XXVII) that we observed with the Large Binocular Cameras of the Large Binocular Telescope. In the field of And XXVII we have discovered a total of 90 variables: 89 RR Lyrae stars and 1 Anomalous Cepheid. The average period of the fundamental mode RR Lyrae stars (RRab) =0.59 {days} (σ = 0.05 day) and the period-amplitude diagram place And XXVII in the class of Oosterhoff I/Intermediate objects. Combining information from the color-magnitude diagram (CMD) and the variable stars, we find evidence for a single old and metal-poor stellar population with [Fe/H] ˜ -1.8 dex and t ˜ 13 Gyr in And XXVII. The spatial distributions of RR Lyrae and red giant branch (RGB) stars give clear indication that And XXVII is a completely disrupted system. This is also supported by the spread observed along the line of sight in the distance to the RR Lyrae stars. The highest concentration of RGB and RR Lyrae stars is found in a circular area of 4 arcmin in radius, centered about 0.°2 in the southeast direction from Richardson et al.’s center coordinates of And XXVII. The CMD of this region is well-defined, with a prominent RGB and 15 RR Lyrae stars (out of the 18 found in the region) tracing a very tight horizontal branch at =25.24 {mag} σ = 0.06 mag (average over 15 stars). We show that And XXVII is a strong candidate building block of the M31 halo. Based on data collected with the Large Binocular Cameras at the Large Binocular Telescope, PI: G. Clementini.

  4. Investigation of variable star candidates in the globular cluster NGC 5024 (M53)

    Science.gov (United States)

    Bramich, D. M.; Arellano Ferro, A.; Jaimes, R. Figuera; Giridhar, Sunetra

    2012-08-01

    We have performed a careful investigation of the 74 candidate variable stars presented by Safonova & Stalin. For this purpose we used our data base of imaging and light curves from Arellano Ferro et al. We find that two candidates are known variable stars, eight candidates were discovered first by Arellano Ferro et al., but would not have been known to Safonova & Stalin at the time of their paper submission, while four candidates are new variables. Three of the new variables are SX Phe type and one is a semiregular (SR) type red giant variable. We also tentatively confirm the presence of true variability in two other candidates, and we are unable to investigate another four candidates because they are not in our data base. However, we find that the remaining 54 candidate variable stars are spurious detections where systematic trends in the light curves have been mistaken for true variability. We believe that the erroneous detections are caused by the adoption of a very low detection threshold used to identify these candidates.

  5. KQ Mon and the nature of the UX Ursa Majoris Nova-like variables

    Science.gov (United States)

    Sion, E. M.; Guinan, E. F.

    1983-01-01

    The UX Ursa Majoris stars form a group of nova-like variables with common photometric and spectroscopic properties. These objects appear to be related to the cataclysmic variables. However, there is no information that they have undergone major outbursts. The present investigation is concerned with a new object, KQ Mon, which has been included in a program of study conducted with the IUE satellite. A description of observations of KQ Mon is presented, and the relationship of this star to other UX UMa stars is examined. Attention is given to the nature of the UX Ursa Majoris stars. It is argued that the accretion rates of the UX UMa stars are higher than, for example, the dwarf novae during quiescence and that the higher accretion rates of the UX UMa stars are responsible for their lack of major outbursts.

  6. 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

  7. 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

  8. 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.

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

    International Nuclear Information System (INIS)

    Humphreys, Roberta M.; Davidson, Kris; Hahn, David; Martin, John C.; Weis, Kerstin

    2017-01-01

    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.

  10. Stars

    CERN Document Server

    Kukla, Lauren

    2016-01-01

    Climb Aboard! Explore planets and how they are formed! Meet key astronomers! Examine the history of mapping the stars! Investigate red giants, black and white dwarfs, neutron stars, supernovas, and black holes! See an infographic showing our solar system's statistics! Did You Know? facts and a Guidebook of the brightest stars complete your journey. Aligned to Common Core standards and correlated to state standards. Checkerboard Library is an imprint of Abdo Publishing, a division of ABDO.

  11. 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

  12. 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.

  13. 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

  14. 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

  15. Mid-Infrared Studies of the Variability of the Dustiest, Most Extreme Asymptotic Giant Branch Stars in the Magellanic Clouds

    Science.gov (United States)

    Sargent, Benjamin A.; Meixner, Margaret; Jones, Olivia

    2017-01-01

    The asymptotic giant branch (AGB) phase is one of the last phases of a star’s life. AGB stars lose mass in an outflow in which dust condenses and is pushed away from the star. Extreme AGB stars are so named because their very red colors suggest very large amounts of dust, which in turn suggests extremely high mass-loss rates. AGB stars also vary in their brightness, and studies show that extreme AGB stars tend to have longer periods than other AGB stars and are more likely to be fundamental mode pulsators. The variability of extreme AGB stars must be explored at infrared wavelengths, as the copious amounts of circumstellar dust renders them invisible in the optical. Using the Spitzer Space Telescope, we have observed a sample of extreme AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) over Cycles 9 through 12 during the Warm Spitzer mission. For each cycle, we typically observed a set of extreme AGB stars at both 3.6 and 4.5 microns wavelength approximately monthly for most of a year. These observations reveal a wide range of variability properties. Though we targeted a certain number of extreme AGB stars, our observations also monitored other stars in the fields. We present results from our analysis of the data obtained from these Spitzer variability programs.

  16. Infrared Studies of the Variability and Mass Loss of Dusty Asymptotic Giant Branch Stars in the Magellanic Clouds

    Science.gov (United States)

    Sargent, Benjamin; Groenewegen, M. A. T.

    2018-01-01

    The asymptotic giant branch (AGB) phase is one of the last phases of a star's life. AGB stars lose mass in an outflow in which dust condenses and is pushed away from the star. Extreme AGB stars are so named because their very red colors suggest very large amounts of dust, which in turn suggests extremely high mass loss rates. AGB stars also vary in brightness, and studies show that extreme AGB stars tend to have longer periods than other AGB stars and are more likely to be fundamental mode pulsators than other AGB stars. Extreme AGB stars are difficult to study, as their colors are so red due to their copious amounts of circumstellar dust that they are often not detected at optical wavelengths. Therefore, they must be observed at infrared wavelengths to explore their variability. Using the Spitzer Space Telescope, my team and I have observed a sample of extreme AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) over Cycles 9 through 12 during the Warm Spitzer mission. For each cycle, we typically observed a set of extreme AGB stars at both 3.6 and 4.5 microns wavelength approximately monthly for most of a year. These observations reveal a wide range of variability properties. I present results from our analysis of the data obtained from these Spitzer variability programs, including light curve analyses and comparison to period-luminosity diagrams. Funding is acknowledged from JPL RSA # 1561703.

  17. 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 ...

  18. 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.

  19. Variable Stars and Constant Commitments: The Stellar Career of Dorrit Hoffleit

    Science.gov (United States)

    Larsen, Kristine

    2011-05-01

    Astronomer, educator, and science historian Dorrit Hoffleit (1907-2007) was widely respected by the amateur and professional astronomical community as a mentor and an ardent supporter of independent research. Her more than 600 catalogues, books, articles, book reviews, and news columns cover myriad aspects of astronomy, from variable stars and stellar properties to meteor showers, quasars, and rocketry. She also made important contributions to the history of astronomy. Hoffleit worked at the Harvard College Observatory from 1927-1956, where she discovered over 1200 variable stars. When Director Harlow Shapley retired from Harvard, Hoffleit gave up her tenured position and moved to Yale University, where she was placed in charge of the Yale Catalog of Bright Stars. At the same time, she was offered a position as director of the Maria Mitchell Observatory on Nantucket Island in Massachusetts. Hoffleit split her dual positions into six-month stints and remained director at the Mitchell Observatory for 21 years, developing a summer research program that engaged more than 100 undergraduate students (all but three of them women) in variable star research. Up until shortly before her death, she continued to work tirelessly on selected projects, and she was in high demand as a collaborator with colleagues at Yale and elsewhere. She was especially devoted to the American Association of Variable Star Observers (AAVSO) in part because it brought together amateur and professional astronomers in collaboration. She served on the organization's council for 23 years and as its president from 1961-1963. In 2002, the AAVS0 published her autobiography, Misfortunes as Blessings in Disguise, in which Hoffleit explains how she always felt blessed by the opportunities in her life, even those which initially seemed misfortunes, and above all else valued creativity, flexibility, collegiality, and intellectual freedom in her professional life.

  20. 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.

  1. 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...

  2. 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 variability...... degrees. This level of misalignment does not significantly change (and may even improve) the agreement between our reflection results and the thermal continuum results regarding the black hole spin. The spectral variability observed by NuSTAR is dominated by the primary continuum, implying variability...... companion star....

  3. Spitzer and Variable Young Stars: Shining a Spotlight on Circumstellar Disks

    Science.gov (United States)

    Cody, Ann Marie; CSI 2264 Team

    2014-01-01

    Since its launch in 2003, the Spitzer Space Telescope has helped to uncover hundreds of disk bearing young stars in clusters by detecting their infrared excesses. Study of the spectral energy distributions of these objects has shed light on disk evolution, dispersal, and the relationship to planet formation. With the start of the Warm Spitzer Mission, mid-infrared time series observations have opened up a new window into the dynamic nature of these systems. Not only are young stellar objects (YSOs) highly variable, but so are their disks! I will review recent findings on mid-infrared variability in young stars, highlighting the Young Stellar Object Variability project and the joint Spitzer/CoRoT Coordinated Synoptic Investigation of NGC 2264. These efforts have resulted in a comprehensive census and categorization of YSO flux behavior at 0.5 through 4.5 microns, on timescales from hours to months. We now have evidence for multiple simultaneous variability mechanisms, supporting the picture of a highly dynamic star-disk system.

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

    Science.gov (United States)

    Miles, Brittany E.; Shkolnik, Evgenya L.

    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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. A survey of long-term X-ray variability in cool stars

    Science.gov (United States)

    Pye, J.; Rosen, S.; Read, A.; Law-Green, D.; Watson, M.; O'Brien, P.; Garreffa, M.

    2017-10-01

    X-ray variability in cool stars can be indicative of coronal magnetic field changes and reconfiguration from a variety of phenomena, including flare events (typical timescales of minutes - hours), active-region evolution (hours - days - weeks), rotational modulation (hours - days - weeks), and activity cycles (years - decades). As part of the EXTraS project (Exploring the X-ray transient and variable sky - http://www.extras-fp7.eu/ ), we have performed a systematic survey of long-term X-ray variability using the ˜decade-long public database of XMM-Newton observations (3XMM). We are thus focussing here on timescales from ˜a day to ˜a decade, using average flux values from individual XMM-Newton observations. Though the resulting sampling is often highly non-uniform in time, the light-curves can provide valuable insights into the magnetic activity outside of shorter-term flaring episodes. We have taken a number of stellar samples and evaluated statistical properties of the flux distributions, and compared these across, for example spectral type, and with previously-published estimates. We have also examined the potential effects of flare events on the apparent long-term variability estimates. We report here on overall variability distributions and extreme cases, focussing on serendipitously-observed stars (yielding,in some sense an unbiased sample).

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. Flickering of the symbiotic variable CH Cygni during outburst

    International Nuclear Information System (INIS)

    Slovak, M.H.; Africano, J.

    1978-01-01

    High-speed and conventional BVRI photometry are reported for the bright symbiotic variable CH Cygni (M6 IIIe), obtained during the course of a recent outburst. Unlike the quiescent symbiotic stars, the presence of flickering similar in nature to that seen in the cataclysmic variables has been confirmed during this active phase. The BVRI photometry for a sample of stars in the field is used to derive the reddening and the distance to CH Cyg. A composite energy distribution is derived from 0.35 to 11.0 μm which clearly establishes the existence of a variable, blue continuum. The lack of variability in the near infrared suggests that the blue continuum arises from a hot companion. A binary model including a subluminous hot companion accreting material from the stellar wind of an SRa variable is discussed to account for the observed photometric properties. (author)

  15. 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.

  16. MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

    Directory of Open Access Journals (Sweden)

    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.

  17. 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.

  18. 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.

  19. 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 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.

  20. 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 <2.3 min was 58.5 h, with additional data with lower cadence. We 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.

  1. Spectroscopy of the red star in IP Peg

    International Nuclear Information System (INIS)

    Martin, J.S.; Jones, D.H.P.; Friend, M.T.; Smith, R.C.

    1989-01-01

    CCD spectroscopy of the cataclysmic variable IP Pegasi during decline from outburst shows narrow chromospheric emission lines from the irradiated face of the red star. The He I (7065 A) emission line is used to produce a partial radial velocity curve, with K He =293.2±3.3 km s -1 . A reanalysis of previous Na I doublet (8190 A) absorption line data produces a considerably larger semi-amplitude, K abs , than previously published. However, this is larger than the true semi-amplitude, K 2 , because irradiation from the disc ionizes the NaI on the inner face of the red star and decreases the strength of the NaI doublet on that face. A computer simulation of the secondary radial velocity curve, including this ionization effect, is used to estimate the true semi-amplitude of the secondary motion. This gives K 2 =298±8 km s -1 . (author)

  2. Automated Photometry, Period Analysis and Flare-up Constraints for Selected Mira Variable Stars

    Science.gov (United States)

    Mais, D. E.; Stencel, R. E.; Richards, D.

    2005-05-01

    During the course of the past two years, 108 selected Mira-type program stars have been monitored to address potential flare up episodes. These include 34 M-type, 17-S type and 57 C-type Mira's. This paper will describe the greater than 140,000 magnitude determinations that have been obtained, many closely spaced in time, which are being used to further constrain the potential occurrences of flare-up events. Random reports in the literature suggest that some Mira variables may go through flare up stages, which result in brightening on the order of several tenths of a magnitude or more, and may last hours to days in length. Very little is known about these events and their frequency, indeed, it is not clear that these events are real or instrumental phenomena. The light curves of many of the program stars show a Cepheid like bump phenomenon, usually on the ascending part of the light curve. In general, these bumps appear in longer period Mira's (>350 days) as pointed out by Melikian in 1999. Bumps are not obvious or easily seen in visual data records, although slope changes during rising phase are seen in some cases. In order to address the reality of these events, we established an automated acquisition/analysis of a group of 108 Mira variables [M(oxygen), S and C types] in order to obtain the densest possible coverage of the periods, to better constrain the character and frequency of flare-ups. Telescope control scripts were put in place along with real time analysis. This allowed for unattended acquisition of data on every clear night, all night long, in the V, R and I photometric bands. In addition, during the course of most nights, multiple determinations are often obtained for a given star. We are grateful to the estate of William Herschel Womble for partial support of these efforts.

  3. Application of multivariate analysis methods to search for variable stars in the Pi of the Sky experiment

    Science.gov (United States)

    Obara, Lukasz

    2017-08-01

    The purpose of this article is to present novel algorithm for searching variable stars in the Pi of the Sky data, based on Multivariate Analysis (MVA). Pi of the Sky is a system of wide field-of-view robotic telescopes, which search for short timescale astrophysical phenomena, especially for prompt optical emission from GRB. The system was designed for autonomous operation, monitoring a large fraction of the sky with 12m -13m range and time resolution of the order of 1 - 100 seconds. Dedicated photometric algorithm was implemented in the LUIZA framework and optimized on a sample of test sky images. It was then used on a "training" image sample, which was obtained by modifying the test sample of images, using different patterns of variability to selected constant stars. Different statistical estimators were considered to find the most efficient algorithm, based on MVA method, for variable star identification. Analysis of the test results indicated that most efficient candidate star selection can be based on the so called Boosted Decision Tree (BDT) approach. The algorithm is then used to search for variable star candidates in the actual data. New results of the analysis and three candidate stars found are presented.

  4. 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.

  5. 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.

  6. 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

    In this paper, we present the analysis of time-series observations from 2013 and 2014 of five metal rich ([Fe/H] $>$ -1) globular clusters: NGC~6388, NGC~6441, NGC~6528, NGC~6638, and NGC~6652. The data have been used to perform a census of the variable stars in the central parts of these clusters....... 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...... known or suspected variable stars in the central regions of the five clusters. Furthermore, we were able to identify, and in most cases classify 48, 49, 7, 8, and 2 previously unknown variables in NGC~6388, NGC~6441, NGC~6528, NGC~6638, and NGC~6652, respectively. Especially interesting is the case...

  7. 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...

  8. 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.

  9. 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...... main groups to describe the observed variety in pulsating A-F type stars: γ Dor, δ Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show...... pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the γ Dor and δ Sct range, also between 5 and 10 d-1, which is a challenge for the current models. We find indications for the existence of δ Sct and γ Dor stars beyond the edges of the current...

  10. [A new automated method to identify emission line star from massive spectra].

    Science.gov (United States)

    Pan, Jing-Chang; Zhang, Cai-Ming; Wei, Peng; Luo, A-Li; Zhao, Yong-Heng

    2012-06-01

    Stellar spectra are characterized by obvious absorption lines or absorption bands, while those with emission lines are usually special stars such as cataclysmic variable stars (CVs), HerbigAe/Be etc. The further study of this kind of spectra is meaningful. The present paper proposed a new method to identify emission line stars (ELS) spectra automatically. After the continuum normalization is done for the original spectral flux, line detection is made by comparing the normalized flux with the mean and standard deviation of the flux in its neighbor region The results of the experiment on massive spectra from SDSS DR8 indicate that the method can identify ELS spectra completely and accurately. Since no complex transformation and computation are involved in this method, the identifying process is fast and it is ideal for the ELS detection in large sky survey projects like LAMOST and SDSS.

  11. International conference entitled Zdeněk Kopal’s Binary Star Legacy

    CERN Document Server

    Drechsel, Horst; ZDENEK KOPAL’S BINARY STAR LEGACY

    2005-01-01

    An international conference entitled "Zdenek Kopal's Binary Star Legacy" was held on the occasion of the late Professor Kopal's 90th birthday in his home town of Litomyšl/Czech Republic and dedicated to the memory of one of the leading astronomers of the 20th century. Professor Kopal, who devoted 60 years of his scientific life to the exploration of close binary systems, initiated a breakthrough in this field with his description of binary components as non-spherical stars deformed by gravity, with surfaces following Roche equipotentials. Such knowledge triggered the development of new branches of astrophysics dealing with the structure and evolution of close binaries and the interaction effects displayed by exciting objects such as cataclysmic variables, symbiotic stars or X-ray binaries. Contributions to this conference included praise of the achievements of a great astronomer and personal reminiscences brought forward by Kopal's former students and colleagues, and reflected the state of the art of the dyn...

  12. Circular polarimetry of EXO 033319-2554.2 - a new eclipsing AM Herculis star

    International Nuclear Information System (INIS)

    Berriman, G.; Smith, P.S.

    1988-01-01

    This Letter presents circular polarimetry that unequivocally identifies EXO 033319-2554.2 as only the third eclipsing AM Her star and brings the total number of AM Her stars now identified to 14. The orbital period is 126.4 minutes, as previously reported, and defines a new short-period edge to the period gap seen in all classes of cataclysmic variable stars. EXO 033319-2554.2 shows 2.5 mag deep eclipses of the predominantly accreting magnetic pole on the white dwarf. Before the eclipse, the pole rotates into the line of sight and shows white-light circular polarization, due to cyclotron radiation, that reaches values as high as 10 percent. There is some evidence that the second pole is emitting cyclotron radiation too. How high time resolution photometry, linear polarimetry, and spectroscopy will be of great value in understanding this system. 17 references

  13. 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.

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

    Science.gov (United States)

    Egeland, Ricky

    2017-04-01

    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 to a

  15. CENSUS OF BLUE STARS IN SDSS DR8

    International Nuclear Information System (INIS)

    Scibelli, Samantha; Newberg, Heidi Jo; Carlin, Jeffrey L.; Yanny, Brian

    2014-01-01

    We present a census of the 12,060 spectra of blue objects ((g – r) 0 < –0.25) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies, and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10,856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise ratio, and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf-M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179, quasi-stellar objects (QSOs), and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by eye, and diagnostic plots that show the positions, colors, apparent magnitudes, proper motions, etc., for each classification. Future surveys will be able to use templates similar to stars in each of the classes we identify to automatically classify blue stars, including rare types

  16. Radial-Velocity Variability of the Sun as a Star with HAPRS And HAPRS-N

    Science.gov (United States)

    Haywood, Raphaëlle D.; Collier Cameron, Andrew; Dumusque, Xavier; Glenday, Alex; Latham, David W.; Lovis, Christophe; Maldonado, Jesus; Micela, Giusi; Molinari, Emiliano; Mortier, Annelies; Pepe, Francesco; Phillips, David F.; Udry, Stephane

    2016-06-01

    Since we can resolve the surface of the Sun directly, we can explore the origin of radial-velocity variations induced by individual solar surface features such as faculae/plage, sunspots and granulation.I will present my recent investigation of the radial-velocity variations of the Sun as a star, based on high-resolution HARPS spectra of reflected sunlight and simultaneous images from the Solar Dynamics Observatory. We found that faculae are the dominant source of activity-induced radial-velocity variations, via suppression of convective blueshift. We investigated possible proxies for activity-induced radial-velocity variations and found that optical lightcurves can only provide a partial representation of these signals; the full-disc magnetic flux, however, is an excellent tracer. In addition to this dataset, the HARPS-N spectrograph has been operating with a new solar telescope feed since 2015 July. I will present results from the first year observations, which show radial-velocity variations of up to 7-8 m/s.Identifying proxies for solar radial-velocity variations is key to understanding the radial-velocity variability of other Sun-like stars, and is also essential for other investigations such as exoplanet detection surveys.

  17. Similar star formation rate and metallicity variability timescales 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

    2018-03-01

    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 timescales 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 timescales, are often anti-correlated 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 anti-correlated fashion. This anti-correlated 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.

  18. The nova-like variable KQ Mon and the nature of the UX Ursa Majoris stars

    Science.gov (United States)

    Sion, E. M.; Guinan, E. F.

    1982-01-01

    The KQ Mon is a UX UMa type nova-like variable discovered by Howard Bond. Optical spectra taken by Bond in 1978 reveal very shallow Balmer absorption lines and He I absorption. Bond also did UBV and high speed photometry in 1978 and early 1981. There has been no evidence of orbital variations but the appearance of the optical spectrum and the presence of low amplitude flickering suggested a strong similarity to CD-42-14462 (=V3885 Sgr) and other members of the UX UMa class. Low dispersion observations of KQ Mon were made with the International Ultraviolet Explorer satellite. Six spectra taken with the shot wavelength prime camera are dominated by strong broad absorption lines due to N V, O I, Si III, Si IV, C IV, He II, N IV, and Al III. There is little evidence of orbital phase modulation over the time baseline of the observations. Unlike UV observations of other UX UMa type objects, KQ Mon exhibits no emission lines or P Cygni type profiles and the velocity displacements appear to be smaller, suggesting the absence of a hot, high velocity wind characterizing other UX UMa stars. The relationship of KQ Mon to other UX UMa disk stars is discussed and a model is suggested to explain their observed properties and the lack of major outbursts.

  19. 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.

  20. Fast Variability in Selected Chromospherically Active Dwarf Stars and Observational Equipment for Their Study

    Science.gov (United States)

    Bogdanovski, Rumen G.

    2015-06-01

    The observations of variable stars, especially those which show fast changes in their brightness, require high speed and high precision photometry. In order to study events like low amplitude optical oscillations and small scale fluctuations in the light curves, synchronous observations are required. These observations have to be carried out simultaneously at two or more, preferably distant, sites (Romanyuk et al., 2001), which allows the identification and elimination of artifacts produced by the equipment and the atmospheric interferences. In this way the fine structure of the light curve is revealed with a significant certainty. In order to study these events a new high speed time synchronized photometric system had to be designed, which addresses the requirements of the observations of high frequency subtle phenomena during stellar flares. It provides remote automatedand centralized control of the photometric equipment over a computer network,as well as remotemonitoring. Furthermore, some preliminary data processing can be performed at the time the data is obtained.

  1. Exploring the SDSS Data Set with Linked Scatter Plots. I. EMP, CEMP, and CV Stars

    Energy Technology Data Exchange (ETDEWEB)

    Carbon, Duane F.; Henze, Christopher; Nelson, Bron C., E-mail: Duane.F.Carbon@nasa.gov [NASA Ames Research Center, NASA Advanced Supercomputing Facility, Moffett Field, CA, 94035-1000 (United States)

    2017-02-01

    We present the results of a search for extremely metal-poor (EMP), carbon-enhanced metal-poor (CEMP), and cataclysmic variable (CV) stars using a new exploration tool based on linked scatter plots (LSPs). Our approach is especially designed to work with very large spectrum data sets such as the SDSS, LAMOST, RAVE, and Gaia data sets, and it can be applied to stellar, galaxy, and quasar spectra. As a demonstration, we conduct our search using the SDSS DR10 data set. We first created a 3326-dimensional phase space containing nearly 2 billion measures of the strengths of over 1600 spectral features in 569,738 SDSS stars. These measures capture essentially all the stellar atomic and molecular species visible at the resolution of SDSS spectra. We show how LSPs can be used to quickly isolate and examine interesting portions of this phase space. To illustrate, we use LSPs coupled with cuts in selected portions of phase space to extract EMP stars, CEMP stars, and CV stars. We present identifications for 59 previously unrecognized candidate EMP stars and 11 previously unrecognized candidate CEMP stars. We also call attention to 2 candidate He ii emission CV stars found by the LSP approach that have not yet been discussed in the literature.

  2. Variability of Disk Emission in Pre-Main Sequence and Related Stars. II. Variability in the Gas and Dust Emission of the Herbig Fe Star SAO 206462

    Science.gov (United States)

    Sitko, Michael L.; Day, Amanda N.; Kimes, Robin L.; Beerman, Lori C.; Martus, Cameron; Lynch, David K.; Russell, Ray W.; Grady, Carol A.; Schneider, Glenn; Lisse, Carey M.; hide

    2011-01-01

    We present thirteen epochs of near-infrared (0.8-5 microns) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Br(alpha) , Br(gamma), Pa(beta), Pa(delta), Pa(epsilon), and the 0.8446 microns line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 x 10(exp 8)Solar Mass/yr was derived from the Br(gamma) and Pa(beta) lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only approx.30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 microns was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on time scales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magneto-rotational) would operate there on longer time scales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on time scales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer time scales that have been sampled so far.

  3. Radial velocity variability and stellar properties of FGK stars in the cores of NGC 2516 and NGC 2422

    Science.gov (United States)

    Bailey, John I.; Mateo, Mario; White, Russel J.; Shectman, Stephen A.; Crane, Jeffrey D.

    2018-04-01

    We present multi-epoch high-dispersion optical spectra obtained with the Michigan/Magellan Fibre System of 126 and 125 Sun-like stars in the young clusters NGC 2516 (141 Myr) and NGC 2422 (73 Myr). We determine stellar properties including radial velocity (RV), Teff, [Fe/H], [α/Fe] and the line-of-sight rotation rate, vrsin (i), from these spectra. Our median RV precision of 80 m s-1 on individual epochs that span a temporal baseline of 1.1 yr enables us to investigate membership and stellar binarity, and to search for sub-stellar companions. We determine membership probabilities and RV variability probabilities for our sample along with candidate companion orbital periods for a select subset of stars. In NGC 2516, we identified 81 RV members, 27 spectroscopic binaries (17 previously identified as photometric binaries) and 16 other stars that show significant RV variability after accounting for average stellar jitter at the 74 m s-1 level. In NGC 2422, we identify 57 members, 11 spectroscopic binaries and three other stars that show significant RV variability after accounting for an average jitter of 138 m s-1. We use Monte Carlo simulations to verify our stellar jitter measurements, determine the proportion of exoplanets and stellar companions to which we are sensitive, and estimate companion-mass limits for our targets. We also report mean cluster metallicity, velocity and velocity dispersion based on our member targets. We identify 58 non-member stars as RV variables, 24 of which have RV amplitudes that imply stellar or brown-dwarf mass companions. Finally, we note the discovery of a separate RV clustering of stars in our NGC 2422 sample.

  4. The multi-layer variable absorbers in NGC 1365 revealed by XMM-Newton and NuSTAR

    DEFF Research Database (Denmark)

    Rivers, E.; Risaliti, G.; Walton, D. J.

    2015-01-01

    Between 2012 July and 2013 February, NuSTAR and XMM-Newton performed four long-look joint observations of the type 1.8 Seyfert, NGC 1365. We have analyzed the variable absorption seen in these observations in order to characterize the geometry of the absorbing material. Two of the observations...

  5. 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.

  6. 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

  7. 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.

  8. BONA FIDE, STRONG-VARIABLE GALACTIC LUMINOUS BLUE VARIABLE STARS ARE FAST ROTATORS: DETECTION OF A HIGH ROTATIONAL VELOCITY IN HR CARINAE

    International Nuclear Information System (INIS)

    Groh, J. H.; Damineli, A.; Moises, A. P.; Teodoro, M.; Hillier, D. J.; Barba, R.; Fernandez-Lajus, E.; Gamen, R. C.; Solivella, G.

    2009-01-01

    We report optical observations of the luminous blue variable (LBV) HR Carinae which show that the star has reached a visual minimum phase in 2009. More importantly, we detected absorptions due to Si IV λλ4088-4116. To match their observed line profiles from 2009 May, a high rotational velocity of v rot ≅ 150 ± 20 km s -1 is needed (assuming an inclination angle of 30 deg.), implying that HR Car rotates at ≅0.88 ± 0.2 of its critical velocity for breakup (v crit ). Our results suggest that fast rotation is typical in all strong-variable, bona fide galactic LBVs, which present S-Dor-type variability. Strong-variable LBVs are located in a well-defined region of the HR diagram during visual minimum (the 'LBV minimum instability strip'). We suggest this region corresponds to where v crit is reached. To the left of this strip, a forbidden zone with v rot /v crit >1 is present, explaining why no LBVs are detected in this zone. Since dormant/ex LBVs like P Cygni and HD 168625 have low v rot , we propose that LBVs can be separated into two groups: fast-rotating, strong-variable stars showing S-Dor cycles (such as AG Car and HR Car) and slow-rotating stars with much less variability (such as P Cygni and HD 168625). We speculate that supernova (SN) progenitors which had S-Dor cycles before exploding (such as in SN 2001ig, SN 2003bg, and SN 2005gj) could have been fast rotators. We suggest that the potential difficulty of fast-rotating Galactic LBVs to lose angular momentum is additional evidence that such stars could explode during the LBV phase.

  9. A Survey for Stellar Variability in the Inner Regions of M3: An application of image subtraction

    Science.gov (United States)

    Uglesich, R.; Mirabal, N.; Sugerman, B.; Crotts, A.

    2000-05-01

    Globular clusters are useful laboratories for the study of extreme stellar dynamical effects in high density environments as well as stellar evolution. Binary stars are dynamically important populations in globulars and even a small change (on the order of a few %) in their relative frequency can dramatically alter the long term evolution of the cluster (Heggie & Aarseth 1992). A census of the short-period binary systems as well as the number of cataclysmic variables in a globular cluster provides important constraints on models of their dynamical evolution. Here we present results from a study for stellar variability in M3 conducted with the MDM 1.3m telescope. The data were processed with the image subtraction technique of Tomaney & Crotts (1996) which allows us to remove the background of non-variable sources, preserving only signals from the relatively few variables. In the inner 1 sq. arcminute, Guhathakurta et al. (1994) discovered 40 variable stars, whereas we have been able to monitor 72 (primarily RR Lyrae) in this same region. We present light curves for our detected variables as well as some upper limits on the detection of cataclysmic variables within the half-mass radius of the cluster. We show that ground-based image subtraction studies can match, if not exceed, the performance of HST and do so in a much more economical manner which suggests the possibility of systematic ground-based surveys of the cores of most Galactic globular clusters.

  10. Krakatoa Erupts!: Using a Historic Cataclysm to Teach Modern Science

    Science.gov (United States)

    Clary, Renee; Wandersee, James

    2011-01-01

    Through integration of geology, biology, chemistry, and the history of science, the historic Krakatoa eruption offers a unique portal for student inquiry in the classroom. Students are inherently fascinated by natural disasters, and modern comparisons to the Krakatoa cataclysm are as close as the day's news. This article uses the historic Krakatoa…

  11. Intermediate polars as low-field magnetic cataclysmic variables

    International Nuclear Information System (INIS)

    Wickramasinghe, D.T.; Kinwah Wu; Ferrario, Lilia

    1991-01-01

    We present the first detailed calculations of the polarization properties of extended accretion shocks on the surface of a magnetic white dwarf where allowance is made both for field spread and for the change in shock height as a function of specific accretion rate. These results are used to show conclusively that the null detection of circular polarization in most IPs imply fields of less than 5 MG. We suggest that the X-ray properties of MCVs depends critically on the fractional area of the white-dwarf surface over which accretion occurs, and on the type of accretion (smooth or clumpy). We argue that in the known IPs, accretion occurs via a disc. The accretion flow is smooth and a strong shock forms making them a powerful source of hard X-rays. We propose that there is a new class of MCV distinct from the IPs, where the white dwarf is asynchronous and accretes without a disc in which the accretion is clumpy and the radiation is mainly in the EUV region. (author)

  12. Spectral variability of photospheric radiation due to faculae. I. The Sun and Sun-like stars

    Science.gov (United States)

    Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.; Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng

    2017-09-01

    Context. Stellar spectral variability on timescales of a day and longer, arising from magnetic surface features such as dark spots and bright faculae, is an important noise source when characterising extra-solar planets. Current 1D models of faculae do not capture the geometric properties and fail to reproduce observed solar facular contrasts. Magnetoconvection simulations provide facular contrasts accounting for geometry. Aims: We calculate facular contrast spectra from magnetoconvection models of the solar photosphere with a view to improve (a) future parameter determinations for planets with early G type host stars and (b) reconstructions of solar spectral variability. Methods: Regions of a solar twin (G2, log g = 4.44) atmosphere with a range of initial average vertical magnetic fields (100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics code, MURaM, and synthetic intensity spectra were calculated from the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the ATLAS9 radiative transfer code. Nine viewing angles were investigated to account for facular positions across most of the stellar disc. Results: Contrasts of the radiation from simulation boxes with different levels of magnetic flux relative to an atmosphere with no magnetic field are a complicated function of position, wavelength and magnetic field strength that is not reproduced by 1D facular models. Generally, contrasts increase towards the limb, but at UV wavelengths a saturation and decrease are observed close to the limb. Contrasts also increase strongly from the visible to the UV; there is a rich spectral dependence, with marked peaks in molecular bands and strong spectral lines. At disc centre, a complex relationship with magnetic field was found and areas of strong magnetic field can appear either dark or bright, depending on wavelength. Spectra calculated for a wide variety of magnetic fluxes will also serve to improve total and spectral solar irradiance

  13. 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.

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

    NARCIS (Netherlands)

    Uytterhoeven, K.; Moya, A.; Grigahcène, A.; Guzik, J.A.; Gutiérrez-Soto, J.; Smalley, B.; Handler, G.; Balona, L.A.; Niemczura, E.; Fox Machado, L.; Benatti, S.; Chapellier, E.; Tkachenko, A.; Szabó, R.; Suárez, J.C.; Ripepi, V.; Pascual, J.; Mathias, P.; Martín-Ruíz, S.; Lehmann, H.; Jackiewicz, J.; Hekker, S.; Gruberbauer, M.; García, R.A.; Dumusque, X.; Díaz-Fraile, D.; Bradley, P.; Antoci, V.; Roth, M.; Leroy, B.; Murphy, S.J.; De Cat, P.; Cuypers, J.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Breger, M.; Pigulski, A.; Kiss, L.L.; Still, M.; Thompson, S.E.; Van Cleve, J.

    2011-01-01

    Context. The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. Aims. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750

  15. 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

  16. Initial results from NuSTAR observations of the Norma arm

    DEFF Research Database (Denmark)

    Bodaghee, Arash; Tomsick, John A.; Krivonos, Roman

    2014-01-01

    Results are presented for an initial survey of the Norma Arm gathered with the focusing hard X-ray telescope NuSTAR. The survey covers 0.2 deg2 of sky area in the 3-79 keV range with a minimum and maximum raw depth of 15 ks and 135 ks, respectively. Besides a bright black-hole X-ray binary......-wavelength counterpart, it could be a distant X-ray binary or possibly a magnetar. CXOU J163355.1-473804 features a helium-like iron line at 6.7 keV and is classified as a nearby cataclysmic variable. Additional surveys are planned for the Norma Arm and Galactic Center, and those NuSTAR observations will benefit from...

  17. Initial results from NuSTAR observations of the Norma arm

    DEFF Research Database (Denmark)

    Bodaghee, Arash; Tomsick, John A.; Krivonos, Roman

    2014-01-01

    Results are presented for an initial survey of the Norma Arm gathered with the focusing hard X-Ray Telescope NuSTAR. The survey covers 0.2 deg(2) of sky area in the 3-79 keV range with a minimum and maximum raw depth of 15 ks and 135 ks, respectively. Besides a bright black-hole X-ray binary......-wavelength counterpart, it could be a distant X-ray binary or possibly a magnetar. CXOU J163355.1-473804 features a helium-like iron line at 6.7 keV and is classified as a nearby cataclysmic variable. Additional surveys are planned for the Norma Arm and Galactic Center, and those NuSTAR observations will benefit from...

  18. Short-term variability and mass loss in Be stars. I. BRITE satellite photometry of η and μ Centauri

    Science.gov (United States)

    Baade, D.; Rivinius, Th.; Pigulski, A.; Carciofi, A. C.; Martayan, Ch.; Moffat, A. F. J.; Wade, G. A.; Weiss, W. W.; Grunhut, J.; Handler, G.; Kuschnig, R.; Mehner, A.; Pablo, H.; Popowicz, A.; Rucinski, S.; Whittaker, G.

    2016-04-01

    Context. Empirical evidence for the involvement of nonradial pulsations (NRPs) in the mass loss from Be stars ranges from (I) a singular case (μ Cen) of repetitive mass ejections triggered by multi-mode beating to (II) several photometric reports about enormous numbers of pulsation modes that suddenly appear during outbursts and on to (III) effective single-mode pulsators. Aims: The purpose of this study is to develop a more detailed empirical description of the star-to-disk mass transfer and to check the hypothesis that spates of transient nonradial pulsation modes accompany and even drive mass-loss episodes. Methods: The BRITE Constellation of nanosatellites was used to obtain mmag photometry of the Be stars η and μ Cen. Results: In the low-inclination star μ Cen, light pollution by variable amounts of near-stellar matter prevented any new insights into the variability and other properties of the central star. In the equator-on star η Cen, BRITE photometry and Heros echelle spectroscopy from the 1990s reveal an intricate clockwork of star-disk interactions. The mass transfer is modulated with the frequency difference of two NRP modes and an amplitude three times as large as the amplitude sum of the two NRP modes. This process feeds a high-amplitude circumstellar activity running with the incoherent and slightly lower so-called Štefl frequency. The mass-loss-modulation cycles are tightly coupled to variations in the value of the Štefl frequency and in its amplitude, albeit with strongly drifting phase differences. Conclusions: The observations are well described by the decomposition of the mass loss into a pulsation-related engine in the star and a viscosity-dominated engine in the circumstellar disk. Arguments are developed that large-scale gas-circulation flows occur at the interface. The propagation rates of these eddies manifest themselves as Štefl frequencies. Bursts in power spectra during mass-loss events can be understood as the noise inherent to

  19. Variability of Young Stars: the Importance of Keeping an Eye on Children

    Science.gov (United States)

    Herbst, W.

    2013-06-01

    (Abstract only) I will review the state of our understanding of young stars with an emphasis on how and why they vary in brightness. The main causes of the variations will be reviewed, including the rotation of spotted weak-lined T Tauri stars, accretion onto classical T Tauri stars, the eruptive behavior of FUors, and the enigmatic variations of the UXors. The important role that amateurs have and will continue to play in these studies is highlighted. I will also discuss the latest results on two unusual young binaries, BM Orionis in the Trapezium asterism and KH 15D in NGC 2264.

  20. 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.

  1. 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.

  2. Metallic Line Doubling and van hoof Effect in the Spectra of the Variable Star RR Lyrae

    Science.gov (United States)

    Sefyani Lakrizi, Fouad; Benhida, Abdelmjid; Gillet, Denis; Mathias, phillipe; de France, Thibault; Benkhaldoun, Zouhair; Lazrek, Mohamed; Daassou, Ahmed

    2015-08-01

    The Oukaïmeden observatory is situated at an altitude of 2700m in the High Atlas mountain range, 78km south of Marrakech 7°52’52’’ west and 31°12’32’’ north. The quality of the sky is considered exceptional, not only for imaging but also for photometry. Indeed, the average measured seeing is of the order of 1 arc second which ensures high quality spectrum recording with a good signal-to-noise ratio. In this communication, we will present our observations of the phenomenon of metallic absorption lines, doubling in the spectra of the variable star RR Lyrae on Fe II (l4923.921 Å), as well as of sodium D lines. In emission, we observed the lines of hydrogen Hα, Hβ and Hγ with a very strong intensity (50 % above the continuum). We also observed the Van Hoof effect which consists of a difference between the radial velocity of the line of the Fe II (λ4923.921 Å) and that of the line Hβ. These observations were carried out with a small spectrograph of approximately 12000 resolution, installed on a 14 inch telescope, during the night of October 12th 2013. This date corresponded to the maximal phase of the Blazhko cycle. The doubling of the lines was interpreted by Schwarzschild on the basis of an atmosphere in two layers. Based on this interpretation we were able to measure the radial velocity of the shock wave deducted from the difference between both red and blue spectral components on the lines Hα of hydrogen, D of the sodium and the Fe II during the doubling of observed lines. The shock wave reached the maximal speed of 160 kms-1 so confirming the hypersonic regime to which atmosphere is submitted during this maximum phase of the Blazhko cycle. We will also present a comparison of our results with those obtained with high resolution spectrographs and thus confirm the validity of our results.

  3. LUMINOUS AND VARIABLE STARS IN M31 AND M33. I. THE WARM HYPERGIANTS AND POST-RED SUPERGIANT EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Humphreys, Roberta M.; Davidson, Kris; Grammer, Skyler; Kneeland, Nathan [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Martin, John C. [University of Illinois, Springfield, IL (United States); Weis, Kerstin; Burggraf, Birgitta, E-mail: roberta@umn.edu [Astronomical Institute, Ruhr-Universitaet Bochum (Germany)

    2013-08-10

    The progenitors of Type IIP supernovae (SNe) have an apparent upper limit to their initial masses of about 20 M{sub Sun }, suggesting that the most massive red supergiants evolve to warmer temperatures before their terminal explosion. But very few post-red supergiants are known. We have identified a small group of luminous stars in M31 and M33 that are candidates for post-red supergiant evolution. These stars have A-F-type supergiant absorption line spectra and strong hydrogen emission. Their spectra are also distinguished by the Ca II triplet and [Ca II] doublet in emission formed in a low-density circumstellar environment. They all have significant near- and mid-infrared excess radiation due to free-free emission and thermal emission from dust. We estimate the amount of mass they have shed and discuss their wind parameters and mass loss rates, which range from a few Multiplication-Sign 10{sup -6} to 10{sup -4} M{sub Sun} yr{sup -1}. On an H-R diagram, these stars will overlap the region of the luminous blue variables (LBVs) at maximum light; however, the warm hypergiants are not LBVs. Their non-spherical winds are not optically thick, and they have not exhibited any significant variability. We suggest, however, that the warm hypergiants may be the progenitors of the ''less luminous'' LBVs such as R71 and even SN1987A.

  4. LONG-ORBITAL-PERIOD PREPOLARS CONTAINING EARLY K-TYPE DONOR STARS. BOTTLENECK ACCRETION MECHANISM IN ACTION

    International Nuclear Information System (INIS)

    Tovmassian, G.; González–Buitrago, D.; Zharikov, S.; Reichart, D. E.; Haislip, J. B.; Ivarsen, K. M.; LaCluyze, A. P.; Moore, J. P.; Miroshnichenko, A. S.

    2016-01-01

    We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from the active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf’s magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems

  5. Study of Molecular Clouds, Variable Stars and Related Topics at NUU and UBAI

    Science.gov (United States)

    Hojaev, A. S.

    2017-07-01

    The search of young PMS stars made by our team at Maidanak, Lulin and Beijing observatories, especially in NGC 6820/23 area, as well as monitoring of a sample of open clusters will be described and results will be presented. We consider physical conditions in different star forming regions, particularly in TDC and around Vul OB1, estimate SFE and SFR, energy balance and instability processes in these regions. We also reviewed all data on molecular clouds in the Galaxy and in other galaxies where the clouds were observed to prepare general catalog of molecular clouds, to study physical conditions, unsteadiness and possible star formation in them, the formation and evolution of molecular cloud systems, to analyze their role in formation of different types of galaxies and structural features therein.

  6. K2 variable catalogue - II. Machine learning classification of variable stars and eclipsing binaries in K2 fields 0-4

    Science.gov (United States)

    Armstrong, D. J.; Kirk, J.; Lam, K. W. F.; McCormac, J.; Osborn, H. P.; Spake, J.; Walker, S.; Brown, D. J. A.; Kristiansen, M. H.; Pollacco, D.; West, R.; Wheatley, P. J.

    2016-02-01

    We are entering an era of unprecedented quantities of data from current and planned survey telescopes. To maximize the potential of such surveys, automated data analysis techniques are required. Here we implement a new methodology for variable star classification, through the combination of Kohonen Self-Organizing Maps (SOMs, an unsupervised machine learning algorithm) and the more common Random Forest (RF) supervised machine learning technique. We apply this method to data from the K2 mission fields 0-4, finding 154 ab-type RR Lyraes (10 newly discovered), 377 δ Scuti pulsators, 133 γ Doradus pulsators, 183 detached eclipsing binaries, 290 semidetached or contact eclipsing binaries and 9399 other periodic (mostly spot-modulated) sources, once class significance cuts are taken into account. We present light-curve features for all K2 stellar targets, including their three strongest detected frequencies, which can be used to study stellar rotation periods where the observed variability arises from spot modulation. The resulting catalogue of variable stars, classes, and associated data features are made available online. We publish our SOM code in PYTHON as part of the open source PYMVPA package, which in combination with already available RF modules can be easily used to recreate the method.

  7. Interpretation of the variability of the beta Cephei star lambda Scorpii : I: The multiple character

    NARCIS (Netherlands)

    Uytterhoeven, K.; Willems, B.; Lefever, K.; Aerts, C.C.; Telting, J.H.; Kolb, U.

    2004-01-01

    We derive accurate values of the orbital parameters of the close binary beta Cephei star lambda Scorpii. Moreover, we present the first determination of the properties of the triple system to which. Scorpii belongs. Our analysis is based on a time series of 815 high-resolution spectra, covering a

  8. 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

  9. Automated Classification of Variable Stars in the Asteroseismology Program of the Kepler Space Mission

    DEFF Research Database (Denmark)

    Blomme, J.; Debosscher, J.; De Ridder, J.

    2010-01-01

    We present the first results of the application of supervised classification methods to the Kepler Q1 long-cadence light curves of a subsample of 2288 stars measured in the asteroseismology program of the mission. The methods, originally developed in the framework of the CoRoT and Gaia space...

  10. MULTI-EPOCH HUBBLE SPACE TELESCOPE OBSERVATIONS OF IZw18: CHARACTERIZATION OF VARIABLE STARS AT ULTRA-LOW METALLICITIES

    International Nuclear Information System (INIS)

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

    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 galaxy. We classify three of them as Classical Cepheids, with periods of 8.71, 125.0, and 130.3 days, respectively, and other two as long period variables with periodicities longer than 100 days. These are the lowest metallicity Classical Cepheids known so far, thus providing the opportunity to explore and fit models of stellar pulsation for Classical Cepheids at previously inaccessible metallicities. The period distribution of the confirmed Cepheids is markedly different from what is seen in other nearby galaxies, which is likely related to the star bursting nature of IZw18. The long period Cepheids we have detected in IZw18 seem to indicate that massive stars at the metallicity of IZw18 (Z = 0.0004) may cross the instability strip long enough to be observed. By applying to the 8.71 days Cepheid theoretical Wesenheit (V, I) relations based on new pulsation models of Classical Cepheids specifically computed for the extremely low metallicity of this galaxy (Z = 0.0004, Y = 0.24), we estimate the distance modulus of IZw18 to be μ 0 = 31.4 ± 0.3 (D = 19.0 +2.8 -2.5 Mpc) for canonical models of Classical Cepheids, and of 31.2 ± 0.3 mag (D = 17.4 +2.6 -2.2 Mpc) using over luminous models. The theoretical modeling of the star's light curves provides μ 0 = 31.4± 0.2 mag, D = 19.0 +1.8 -1.7 Mpc, in good agreement with the results from the theoretical Wesenheit relations. These pulsation distances bracket the distance of 18.2 ±1.5 Mpc inferred by Aloisi et al. using the galaxy's red giant branch tip.

  11. 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.

  12. 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.

  13. 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.

  14. Spectroscopic confirmation of the first symbiotic star in a globular cluster

    Science.gov (United States)

    Zurek, David

    2013-10-01

    We have recently discovered an 18-minute period in the ultraviolet of a star in the globular cluster NGC 1851. In the redder optical bands, this star is red and bright, while it shows a clear UV excess relative to other stars at similar positions in the HR diagram. The system is most likely a symbiotic binary, composed of a cool evolved star and a white dwarf, with an 18 minute spin period, accreting the cool star's wind. The binary would be the first such object ever found in a globular cluster, and only the third in the Galaxy where the white dwarf spin period is measured. The only viable alternatives are that the two components are a chance superposition - something with a nontrivial chance of happening in a globular cluster core. In such a case, the 18 minute period would most likely be the spin period of a magnetic white dwarf in an intermediate polar cataclysmic variable {this would be the first confirmed magnetic CV in a globular cluster}, or the orbital period of a double-degenerate AM CVn binary. Each of these three possibilities show unique {and very different} emission line spectra in the blue wavelength range. Two orbits of HST with STIS/G430L will produce a spectrum of sufficient signal-to-noise to distinguish between these 3 scenarios. The result will be an important constraint on N-body models of globular clusters.

  15. 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.

  16. 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

  17. General Relativity Explains the Shnoll Effect and Makes Possible Forecasting Earthquakes and Weather Cataclysms

    Science.gov (United States)

    Rabounski, Dmitri; Borissova, Larissa

    2014-03-01

    The Shnoll effect is manifested in the fine structure of the noise registered in stable processes, wherein as the magnitude of signal and the average noise remain unchanged. It is periodic fluctuation of the fine structure of the noise according to the cosmic cycles connected with stars, the Sun, and the Moon. The Shnoll effect is explained herein according to General Relativity, as the twin/entangled synchronization states of the observer's reference frame. The states are repeated while the observer travels, in common with the Earth, through the cosmic grid of the geodesic synchronization paths that connect his local reference frame with the reference frames of the other cosmic bodies. These synchronization periods are expected to be existing in the noise of natural processes of any type (physics, biology, social, etc.) and such artificial processes as the random number generation by a computer software. These periods match with the periods of the Shnoll effect. The theory gives not only to explain the Shnoll effect, but also allows forecasting the fluctuations in the stock exchange market, the fluctuations of weather, earthquakes, and other cataclysms.

  18. THE TIME DOMAIN SPECTROSCOPIC SURVEY: VARIABLE SELECTION AND ANTICIPATED RESULTS

    Energy Technology Data Exchange (ETDEWEB)

    Morganson, Eric; Green, Paul J. [Harvard Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 (United States); Anderson, Scott F.; Ruan, John J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Myers, Adam D. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Eracleous, Michael; Brandt, William Nielsen [Department of Astronomy and Astrophysics, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802 (United States); Kelly, Brandon [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106-9530 (United States); Badenes, Carlos [Department of Physics and Astronomy and Pittsburgh Particle Physics, Astrophysics and Cosmology Center (PITT PACC), University of Pittsburgh, 3941 O’Hara St, Pittsburgh, PA 15260 (United States); Bañados, Eduardo [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Blanton, Michael R. [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Bershady, Matthew A. [Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706 (United States); Borissova, Jura [Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030, and Millennium Institute of Astrophysics (MAS), Santiago (Chile); Burgett, William S. [GMTO Corp, Suite 300, 251 S. Lake Ave, Pasadena, CA 91101 (United States); Chambers, Kenneth, E-mail: emorganson@cfa.harvard.edu [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); and others

    2015-06-20

    We present the selection algorithm and anticipated results for the Time Domain Spectroscopic Survey (TDSS). TDSS is an Sloan Digital Sky Survey (SDSS)-IV Extended Baryon Oscillation Spectroscopic Survey (eBOSS) subproject that will provide initial identification spectra of approximately 220,000 luminosity-variable objects (variable stars and active galactic nuclei across 7500 deg{sup 2} selected from a combination of SDSS and multi-epoch Pan-STARRS1 photometry. TDSS will be the largest spectroscopic survey to explicitly target variable objects, avoiding pre-selection on the basis of colors or detailed modeling of specific variability characteristics. Kernel Density Estimate analysis of our target population performed on SDSS Stripe 82 data suggests our target sample will be 95% pure (meaning 95% of objects we select have genuine luminosity variability of a few magnitudes or more). Our final spectroscopic sample will contain roughly 135,000 quasars and 85,000 stellar variables, approximately 4000 of which will be RR Lyrae stars which may be used as outer Milky Way probes. The variability-selected quasar population has a smoother redshift distribution than a color-selected sample, and variability measurements similar to those we develop here may be used to make more uniform quasar samples in large surveys. The stellar variable targets are distributed fairly uniformly across color space, indicating that TDSS will obtain spectra for a wide variety of stellar variables including pulsating variables, stars with significant chromospheric activity, cataclysmic variables, and eclipsing binaries. TDSS will serve as a pathfinder mission to identify and characterize the multitude of variable objects that will be detected photometrically in even larger variability surveys such as Large Synoptic Survey Telescope.

  19. Carbon Stars

    Indian Academy of Sciences (India)

    Abstract. In this paper, the present state of knowledge of the carbon stars is discussed. Particular attention is given to issues of classification, evolution, variability, populations in our own and other galaxies, and circumstellar material.

  20. Photometric Variability of the mCP Star CS Vir: Evolution of the Rotation Period

    Science.gov (United States)

    Ozuyar, D.; Sener, H. T.; Stevens, I. R.

    2018-01-01

    The aim of this study is to accurately calculate the rotational period of CS Vir by using STEREO observations and investigate a possible period variation of the star with the help of all accessible data. The STEREO data that cover 5-yr time interval between 2007 and 2011 are analysed by means of the Lomb-Scargle and Phase Dispersion Minimization methods. In order to obtain a reliable rotation period and its error value, computational algorithms such as the Levenberg-Marquardt and Monte Carlo simulation algorithms are applied to the data sets. Thus, the rotation period of CS Vir is improved to be 9.29572(12) d by using the 5-yr of combined data set. Also, the light elements are calculated as HJD max = 2454715.975(11) + 9d . 29572(12) × E + 9d . 78(1.13) × 10 - 8 × E 2 by means of the extremum times derived from the STEREO light curves and archives. Moreover, with this study, a period variation is revealed for the first time, and it is found that the period has lengthened by 0.66(8) s y-1, equivalent to 66 s per century. Additionally, a time-scale for a possible spin-down is calculated around τSD 106 yr. The differential rotation and magnetic braking are thought to be responsible of the mentioned rotational deceleration. It is deduced that the spin-down time-scale of the star is nearly three orders of magnitude shorter than its main-sequence lifetime (τMS 109 yr). It is, in return, suggested that the process of increase in the period might be reversible.

  1. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Rivilla, V. M.; Martín-Pintado, J. [Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze (Italy); Chandler, C. J. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Sanz-Forcada, J. [Centro de Astrobiología (CSIC/INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Jiménez-Serra, I. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching (Germany); Forbrich, J., E-mail: rivilla@arcetri.astro.it [Department of Astrophysics, University of Vienna, Türkenschanzstr. 17, 1180 Vienna (Austria)

    2015-08-01

    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{sup −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

  3. OPTICAL STUDIES OF 13 HARD X-RAY SELECTED CATACLYSMIC BINARIES FROM THE SWIFT-BAT SURVEY

    International Nuclear Information System (INIS)

    Halpern, Jules P.; Thorstensen, John R.

    2015-01-01

    From a set of 13 cataclysmic binaries that were discovered in the Swift Burst Alert Telescope (BAT) survey, we conducted time-resolved optical spectroscopy and/or time-series photometry of 11, with the goal of measuring their orbital periods and searching for spin periods. Seven of the objects in this study are new optical identifications. Orbital periods are found for seven targets, ranging from 81 minutes to 20.4 hr. PBC J0706.7+0327 is an AM Herculis star (polar) based on its emission-line variations and large amplitude photometric modulation on the same period. Swift J2341.0+7645 may be a polar, although the evidence here is less secure. Coherent pulsations are detected from two objects, Swift J0503.7−2819 (975 s) and Swift J0614.0+1709 (1412 s and 1530 s, spin and beat periods, respectively), indicating that they are probable intermediate polars (DQ Herculis stars). For two other stars, longer spin periods are tentatively suggested. We also present the discovery of a 2.00 hr X-ray modulation from RX J2015.6+3711, possibly a contributor to Swift J2015.9+3715, and likely a polar

  4. The Rhythm of Fairall 9. I. Observing the Spectral Variability With XMM-Newton and NuSTAR

    Science.gov (United States)

    Lohfink, A. M.; Reynolds, S. C.; Pinto, C.; Alston, W.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Fabian, A.C; Hailey, C. J.; Harrison, F. A.; hide

    2016-01-01

    We present a multi-epoch X-ray spectral analysis of the Seyfert 1 galaxy Fairall 9. Our analysis shows that Fairall 9 displays unique spectral variability in that its ratio residuals to a simple absorbed power law in the 0.510 keV band remain constant with time in spite of large variations in flux. This behavior implies an unchanging source geometry and the same emission processes continuously at work at the timescale probed. With the constraints from NuSTAR on the broad-band spectral shape, it is clear that the soft excess in this source is a superposition of two different processes, one being blurred ionized reflection in the innermost parts of the accretion disk, and the other a continuum component such as a spatially distinct Comptonizing region. Alternatively, a more complex primary Comptonization component together with blurred ionized reflection could be responsible.

  5. Discovery and evolution of an unusual luminous variable star in NGC 3432 (supernova 2000ch)

    Czech Academy of Sciences Publication Activity Database

    Wagner, R. M.; Vrba, F. J.; Henden, A. A.; Canzian, B.; Luginbuhl, C. B.; Filipenko, A. V.; Chornock, R.; Li, W.; Coil, A. L.; Schmidt, G. D.; Smith, P. S.; Starrfield, S.; Klose, S.; Tichá, J.; Tichý, M.; Gorosabel, J.; Hudec, René; Šimon, Vojtěch

    2004-01-01

    Roč. 116, č. 818 (2004), s. 326-336 ISSN 0004-6280 Institutional research plan: CEZ:AV0Z1003909 Keywords : supernova e * luminous blue variables * extragalactic sources Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.900, year: 2004

  6. A Vanishing Star Revisited

    Science.gov (United States)

    1999-07-01

    system NN Ser is now in an evolutionary stage that is referred to as the pre-cataclysmic phase. It will be followed by the cataclysmic phase , during which a gas stream will flow from the larger star to the smaller one. This phenomenon is characterized by frequent and abrupt increase in brightness. While many stars are known that are now in that unstable phase, only a few stars have ever been found to be in the preceding, transitory phase. Of these, NN Ser is the only one that has such a deep eclipse and for which it has now become possible to determine quite well the properties of the two components. NN Ser thus represents a most welcome example of a "missing link" in the theory of stellar evolution. It is therefore of great interest to perform further observations of such a rare object. They will include attempts to obtain more spectra to define the spectral type of the cool star very accurately. This will allow a critical check of current theories of atmospheres and evolutionary computations for the smallest and lightest stars. But for now, Reinhold Häfner looks forward to further nights at Paranal with the ESO astronomers there. "We worked together in a wonderful way during these demanding observations", he said, "and without their great support all of this would have been next to impossible!" Notes [1] These observations were carried out during "guaranteed observing time", allocated to the three German institutes that built the FORS instrument. More details about this instrument and related issues are available in ESO Press Release 14/98. [2] Astronomers designate variable stars according to the constellation in which they are seen in the sky and the order in which they are recognized as having variable brightness. For historical reasons, the first variable star in a given constellation (that is not already known by a greek letter, e.g. "Delta Cephei") is designated as "R" (e.g. "R Coronae Borealis"), the second as "S", etc. until "Z". Then follow "RR", "RS

  7. The Multi-Layer Variable Absorbers in NGC 1365 Revealed by XMM-Newton and NuSTAR

    Science.gov (United States)

    Rivers, E.; Risaliti, G.; Walton, D. J.; Harrison, F.; Arevalo, P.; Baur, F. E.; Boggs, S. E.; Brenneman, L. W.; Brightman, M.; Zhang, W. W.

    2015-01-01

    Between 2012 July and 2013 February, NuSTAR and XMM-Newton performed four long-look joint observations of the type 1.8 Seyfert, NGC 1365. We have analyzed the variable absorption seen in these observations in order to characterize the geometry of the absorbing material. Two of the observations caught NGC 1365 in an unusually low absorption state, revealing complexity in the multi-layer absorber that had previously been hidden. We find the need for three distinct zones of neutral absorption in addition to the two zones of ionized absorption and the Compton-thick torus previously seen in this source. The most prominent absorber is likely associated with broad-line region clouds with column densities of around approximately 10 (sup 23) per square centimeter and a highly clumpy nature as evidenced by an occultation event in 2013 February. We also find evidence of a patchy absorber with a variable column around approximately 10 (sup 22) per square centimeter and a line-of-sight covering fraction of 0.3-0.9, which responds directly to the intrinsic source flux, possibly due to a wind geometry. A full-covering, constant absorber with a low column density of approximately 1 by 10 (sup 22) per square centimeter is also present, though the location of this low density haze is unknown.

  8. Spectral eclipse mapping of the accretion disk in the nova-like variable UX Ursae Majoris

    Science.gov (United States)

    Rutten, R. G. M.; Dhillon, V. S.; Horne, K.; Kuulkers, E.

    1994-01-01

    We analyze narrow-band eclipse light curves of the nova-like cataclysmic variable UX UMa, obtained from low-resolution spectra spanning lambda lambda 3600-9800 A . The light curves for narrow bands in the continuum as well as those for individual spectral lines are treated independently, and are used to construct images of the accretion disk's brightness distribution using the maximum-entropy eclipse-mapping technique. Particular attention is paid to the propagation of statistical uncertainties in the data and to how the analysis may introduce systematic errors in the final result. From the many narrrow band images we have reconstructed the spectra from isolated parts of the accretion disk. These spectra reveal that the inner disk radiates a continuum spectrum which peaks in the near UV and has the hydrogen Balmer lines in absorption (with the exception of H-alpha), whereas the outer disk is much fainter, has a much redder spectrum, and has Balmer emission lines. Our analysis reveals the presence of an uneclipsed component of the total light, whose spectrum is very red and has Balmer lines in emission. This unexpected feature of the eclipse mapping technique offers a new tool for an independent assessment of the secondary star's spectrum in eclipsing cataclysmic variables.

  9. Short-term variability and mass loss in Be stars. III. BRITE and SMEI satellite photometry of 28 Cygni

    Science.gov (United States)

    Baade, D.; Pigulski, A.; Rivinius, Th.; Carciofi, A. C.; Panoglou, D.; Ghoreyshi, M. R.; Handler, G.; Kuschnig, R.; Moffat, A. F. J.; Pablo, H.; Popowicz, A.; Wade, G. A.; Weiss, W. W.; Zwintz, K.

    2018-03-01

    Context. Be stars are important reference laboratories for the investigation of viscous Keplerian discs. In some cases, the disc feeder mechanism involves a combination of non-radial pulsation (NRP) modes. Aims: We seek to understand whether high-cadence photometry can shed further light on the role of NRP modes in facilitating rotation-supported mass loss. Methods: The BRITE-Constellation of nanosatellites obtained mmag photometry of 28 Cygni for 11 months in 2014-2016. We added observations with the Solar Mass Ejection Imager (SMEI) in 2003-2010 and 118 Hα line profiles, half of which were from 2016. Results: For decades, 28 Cyg has exhibited four large-amplitude frequencies: two closely spaced frequencies of spectroscopically confirmed g modes near 1.5 c/d, one slightly lower exophotospheric (Štefl) frequency, and at 0.05 c/d the difference (Δ) frequency between the two g modes. This top-level framework is indistinguishable from η Cen (Paper I), which is also very similar in spectral type, rotation rate, and viewing angle. The circumstellar (Štefl) frequency alone does not seem to be affected by the Δ frequency. The amplitude of the Δ frequency undergoes large variations; around maximum the amount of near-circumstellar matter is increased and the amplitude of the Štefl frequency grows by a factor of a few. During such brightenings dozens of transient spikes appear in the frequency spectrum; these spikes are concentrated into three groups. Only 11 frequencies were common to all years of BRITE observations. Conclusions: Be stars seem to be controlled by several coupled clocks, most of which are not very regular on timescales of weeks to months but function for decades. The combination of g modes to the slow Δ variability and/or the atmospheric response to it appears significantly non-linear. As in η Cen, the Δ variability seems to be mainly responsible for the modulation of the star-to-disc mass transfer in 28 Cyg. A hierarchical set of Δ frequencies

  10. FAR-ULTRAVIOLET SPECTROSCOPY OF THE NOVA-LIKE VARIABLE KQ MONOCEROTIS: A NEW SW SEXTANTIS STAR?

    International Nuclear Information System (INIS)

    Wolfe, Aaron; Sion, Edward M.; Bond, Howard E.

    2013-01-01

    New optical spectra obtained with the SMARTS 1.5 m telescope and archival International Ultraviolet Explorer (IUE) far-ultraviolet (FUV) spectra of the nova-like variable KQ Mon are discussed. The optical spectra reveal Balmer lines in absorption as well as He I absorption superposed on a blue continuum. The 2011 optical spectrum is similar to the KPNO 2.1 m IIDS spectrum we obtained 33 years earlier except that the Balmer and He I absorption is stronger in 2011. Far-ultraviolet IUE spectra reveal deep absorption lines due to C II, Si III, Si IV, C IV, and He II, but no P Cygni profiles indicative of wind outflow. We present the results of the first synthetic spectral analysis of the IUE archival spectra of KQ Mon with realistic optically thick, steady-state, viscous accretion-disk models with vertical structure and high-gravity photosphere models. We find that the photosphere of the white dwarf (WD) contributes very little FUV flux to the spectrum and is overwhelmed by the accretion light of a steady disk. Disk models corresponding to a WD mass of ∼0.6 M ☉ , with an accretion rate of order 10 –9 M ☉ yr –1 and disk inclinations between 60° and 75°, yield distances from the normalization in the range of 144-165 pc. KQ Mon is discussed with respect to other nova-like variables. Its spectroscopic similarity to the FUV spectra of three definite SW Sex stars suggests that it is likely a member of the SW Sex class and lends support to the possibility that the WD is magnetic.

  11. The variable quiescent x-ray emission of the neutron star Transient XTE J1701-462

    NARCIS (Netherlands)

    Fridriksson, J.K.; Homan, J.; Wijnands, R.; Cackett, E.M.; Altamirano, D.; Degenaar, N.; Brown, E.F.; Mendez, R.M.; Belloni, T.M.

    2011-01-01

    We present the results of continued monitoring of the quiescent neutron star low-mass X-ray binary XTE J1701-462 with Chandra and Swift. A new Chandra observation from 2010 October extends our tracking of the neutron star surface temperature from 800 days to 1160 days since the end of an

  12. The Variable Quiescent X-Ray Emission of the Transient Neutron Star XTE J1701-462

    NARCIS (Netherlands)

    Fridriksson, Joel K.; Homan, Jeroen; Wijnands, Rudy; Cackett, Edward M.; Altamirano, Diego; Degenaar, Nathalie; Brown, Edward F.; Mendez, Mariano; Belloni, Tomaso M.

    2011-01-01

    We present the results of continued monitoring of the quiescent neutron star low-mass X-ray binary XTE J1701-462 with Chandra and Swift. A new Chandra observation from 2010 October extends our tracking of the neutron star surface temperature from similar or equal to 800 days to similar or equal to

  13. Kepler sheds new and unprecedented light on the variability of a blue supergiant: Gravity waves in the O9.5Iab star HD 188209

    Science.gov (United States)

    Aerts, C.; Símon-Díaz, S.; Bloemen, S.; Debosscher, J.; Pápics, P. I.; Bryson, S.; Still, M.; Moravveji, E.; Williamson, M. H.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Pallé, P. L.; Christensen-Dalsgaard, J.; Rogers, T. M.

    2017-06-01

    Stellar evolution models are most uncertain for evolved massive stars. Asteroseismology based on high-precision uninterrupted space photometry has become a new way to test the outcome of stellar evolution theory and was recently applied to a multitude of stars, but not yet to massive evolved supergiants.Our aim is to detect, analyse and interpret the photospheric and wind variability of the O9.5 Iab star HD 188209 from Kepler space photometry and long-term high-resolution spectroscopy. We used Kepler scattered-light photometry obtained by the nominal mission during 1460 d to deduce the photometric variability of this O-type supergiant. In addition, we assembled and analysed high-resolution high signal-to-noise spectroscopy taken with four spectrographs during some 1800 d to interpret the temporal spectroscopic variability of the star. The variability of this blue supergiant derived from the scattered-light space photometry is in full in agreement with the one found in the ground-based spectroscopy. We find significant low-frequency variability that is consistently detected in all spectral lines of HD 188209. The photospheric variability propagates into the wind, where it has similar frequencies but slightly higher amplitudes. The morphology of the frequency spectra derived from the long-term photometry and spectroscopy points towards a spectrum of travelling waves with frequency values in the range expected for an evolved O-type star. Convectively-driven internal gravity waves excited in the stellar interior offer the most plausible explanation of the detected variability. Based on photometric observations made with the NASA Kepler satellite and on spectroscopic observations made with four telescopes: the Nordic Optical Telescope operated by NOTSA and the Mercator Telescope operated by the Flemish Community, both at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias, the T13 2.0 m Automatic Spectroscopic

  14. Variability in stellar granulation and convective blueshift with spectral type and magnetic activity . II. From young to old main-sequence K-G-F stars

    Science.gov (United States)

    Meunier, N.; Mignon, L.; Lagrange, A.-M.

    2017-11-01

    Context. The inhibition of small-scale convection in the Sun dominates the long-term radial velocity (RV) variability: it therefore has a critical effect on light exoplanet detectability using RV techniques. Aims: We here extend our previous analysis of stellar convective blueshift and its dependence on magnetic activity to a larger sample of stars in order to extend the Teff range, to study the impact of other stellar properties, and finally to improve the comparison between observed RV jitter and expected RV variations. Methods: We estimate a differential velocity shift for Fe and Ti lines of different depths and derive an absolute convective blueshift using the Sun as a reference for a sample of 360 F7-K4 stars with different properties (age, Teff, metallicity). Results: We confirm the strong variation in convective blueshift with Teff and its dependence on (as shown in the line list in Paper I) activity level. Although we do not observe a significant effect of age or cyclic activity, stars with a higher metallicity tend to have a lower convective blueshift, with a larger effect than expected from numerical simulations. Finally, we estimate that for 71% of the stars in our sample the RV and Log R' _HK variations are compatible with the effect of activity on convection, as observed in the solar case, while for the other stars, other sources (such as binarity or companions) must be invoked to explain the large RV variations. We also confirm a relationship between Log R' _HK and metallicity, which may affect discussions of the possible relationship between metallicity and exoplanets, as RV surveys are biased toward low Log R' _HK and possibly toward high-metallicity stars. Conclusions: We conclude that activity and metallicity strongly affect the small-scale convection levels in stars in the F7-K4 range, with a lower amplitude for the lower mass stars and a larger amplitude for low-metallicity stars. Full Table A.1 is only available at the CDS via anonymous ftp to

  15. 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.

  16. 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

    International Nuclear Information System (INIS)

    Humphreys, Roberta M.; Gordon, Michael S.; Hahn, David; Martin, John C.; Weis, Kerstin

    2017-01-01

    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.

  17. Two bi-stability jumps in theoretical wind models for massive stars and the implications for luminous blue variable supernovae

    Science.gov (United States)

    Petrov, Blagovest; Vink, Jorick S.; Gräfener, Götz

    2016-05-01

    Luminous blue variables (LBVs) have been suggested to be the direct progenitors of supernova Types IIb and IIn, with enhanced mass loss prior to explosion. However, the mechanism of this mass loss is not yet known. Here, we investigate the qualitative behaviour of theoretical stellar wind mass loss as a function of Teff across two bi-stability jumps in blue supergiant regime and also in proximity to the Eddington limit, relevant for LBVs. To investigate the physical ingredients that play a role in the radiative acceleration we calculate blue supergiant wind models with the CMFGEN non-local thermodynamic equilibrium model atmosphere code over an effective temperature range between 30 000 and 8800 K. Although our aim is not to provide new mass-loss rates for BA supergiants, we study and confirm the existence of two bi-stability jumps in mass-loss rates predicted by Vink et al. However, they are found to occur at somewhat lower Teff (20 000 and 9000 K, respectively) than found previously, which would imply that stars may evolve towards lower Teff before strong mass loss is induced by the bi-stability jumps. When the combined effects of the second bi-stability jump and the proximity to Eddington limit are accounted for, we find a dramatic increase in the mass-loss rate by up to a factor of 30. Further investigation of both bi-stability jumps is expected to lead to a better understanding of discrepancies between empirical modelling and theoretical mass-loss rates reported in the literature, and to provide key inputs for the evolution of both normal AB supergiants and LBVs, as well as their subsequent supernova Type II explosions.

  18. Reducing the devastating effects of cataclysmic events: Cooperation

    International Nuclear Information System (INIS)

    Jing Ding; Fong, P.

    1989-01-01

    Natural calamities, including earthquakes, land sinkings, volcanos, floods, tsunamis, hurricanes, avalanches, lightnings, forest fires, are discussed. Their devastating effects can be alleviated by cooperative efforts, sometimes international, among all concerned. The successful earthquake management of the Haicheng event is discussed as an example. Now the authors have environmental calamities, including erosion floods, dam failures, acid rain, ozone depletion, and the global greenhouse effect. There are empirical and theoretical questions about whether the greenhouse effect leads to global warming or polar ice melting. The warming prediction was based on model calculation with an incorrect boundary condition. When corrected with the right boundary condition, the models predict ice melting. The same is borne out in independent static and dynamic theories. Thus, there will be no greenhouse warming, only a sea level rise of up to 200 feet, which is much worse. The only way out is replacing fossil fuels by nuclear power. The nuclear fear is analyzed in terms of the Don Quixote syndrome and Laplace dictum. The lessons of Three Mile Island and Chernobyl actually strengthen the case of nuclear safety. New reactor technology and design will make it even safer. After 250 years of studying the history of the earth, geologists are now able to show that it is nothing but a long series of gradual changes and violent events. What was true in the past will remain so in the future, and cataclysms will occur again and again. Earthquakes, land subsidence and volcanic eruptions; flood and drought; the tsunami, tropical cyclones and avalanches; lightning and forest fires; have occurred ever since mountains, oceans, rivers, atmosphere, and ice sheets have been on the earth, and they will continue to happen

  19. 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.

  20. Radio emission from the nova-like variable AC Cancri and the symbiotic variable AG Draconis

    International Nuclear Information System (INIS)

    Torbett, M.V.; Campbell, B.; Mount Wilson and Las Campanas Observatories, Pasadena, CA)

    1987-01-01

    Radio emission at 6 cm has been detected from the nova-like cataclysmic variable AC Cnc and the symbiotic variable AG Dra. The AC Cnc observation constitutes the first radio detection in this class of objects. The AG Dra source is probably resolved and appears to show asymmetric, extended structure. The radio emission can best be explained by thermal bremsstrahlung. 26 references

  1. Rotationally modulated variability and pulsations of the He-rich star CPD -62°2124 with an extraordinarily strong magnetic field

    Science.gov (United States)

    Hubrig, S.; Mikulášek, Z.; Kholtygin, A. F.; Ilyin, I.; Schöller, M.; Järvinen, S. P.; Scholz, R.-D.; Zejda, M.

    2017-11-01

    A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD -62°2124, which has a fractional main-sequence lifetime of about 60 per cent. Strongly magnetic early-B type chemically peculiar stars in an advanced evolutionary state are of special interest to understand the evolution of the angular momentum and spin-down time-scales in the presence of a global magnetic field. We made use of 17 FORS 2 low-resolution spectropolarimetric observations and 844 ASAS3 photometric measurements for the determination of the rotation period, pulsationsand the magnetic field geometry of the star. We calculated periodograms and applied phenomenological models of photometric, spectral and spectropolarimetric variability. We found that all quantities studied, specifically equivalent widths, the mean longitudinal magnetic field 〈Bz〉 and the flux in the V filter, vary with the same period P = 2.628 d, which was identified as the rotation period. The observed variations can be fully explained by a rigidly rotating main-sequence star with an uneven distribution of chemical elements, photometric spots and a stable, nearly dipolar magnetic field with a polar field strength of about 21 kG, frozen into the body of the star. The magnetic field of CPD -62°2124 is tilted to the rotation axis by β = 28° ± 7°, while the inclination of the rotation axis towards the line of sight is only i = 20° ± 5°. In the acquired FORS 2 spectra, we detect short-term line profile variations indicating the presence of β Cephei type pulsations. As of today, no other pulsating star of this type is known to possess such a strong magnetic field.

  2. 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.

  3. 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.

  4. The Variable Quiescent X-Ray Emission of the Neutron Star Transient XTE J1701-462

    NARCIS (Netherlands)

    Fridriksson, Joel K.; Homan, J.; Wijnands, R.; Cackett, E. M.; Degenaar, N.; Mendez, M.; Altamirano, D.; Brown, E. F.; Belloni, T. M.; Lewin, W. H. G.

    We have monitored the cooling of the neutron star in the transient low-mass X-ray binary XTE J1701-462 with Chandra and XMM-Newton since the source entered quiescence in 2007 after an exceptionally luminous 19-month outburst. A recent Chandra observation made almost 1200 days into quiescence

  5. Mid-Infrared Interferometric Monitoring of Evolved Stars: The Dust Shell Around the Mira Variable RR Aquilae at 13 Epochs

    Science.gov (United States)

    2011-01-01

    Prescribed by ANSI Std Z39-18 A&A 532, A134 (2011) the planetary nebula phase, leaving the core as a white dwarf . Generally many aspects of the...mass loss is important, as AGB stars play a cru- cial role in the chemical enrichment and evolution of galaxies by returning gas and dust to the ISM

  6. 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

  7. A CENSUS OF ROTATION AND VARIABILITY IN L1495: A UNIFORM ANALYSIS OF TRANS-ATLANTIC EXOPLANET SURVEY LIGHT CURVES FOR PRE-MAIN-SEQUENCE STARS IN TAURUS

    International Nuclear Information System (INIS)

    Xiao Hongyu; Covey, Kevin R.; Lloyd, James P.; Rebull, Luisa; Charbonneau, David; Mandushev, Georgi; O'Donovan, Francis; Slesnick, Catherine

    2012-01-01

    We analyze light curves obtained by the Trans-atlantic Exoplanet Survey (TrES) for a field centered on the L1495 dark cloud in Taurus. The Spitzer Taurus Legacy Survey catalog identifies 179 bona fide Taurus members within the TrES field; 48 of the known Taurus members are detected by TrES, as well as 26 candidate members identified by the Spitzer Legacy team. We quantify the variability of each star in our sample using the ratio of the standard deviation of the original light curve (σ orig. ) to the standard deviation of a light curve that has been smoothed by 9 or 1001 epochs (σ 9 and σ 1001 , respectively). Known Taurus members typically demonstrate (σ orig. /σ 9 ) orig. /σ 1001 ) orig. /σ 9 ) ∼ 3.0 and (σ orig. /σ 1001 ) ∼ 10, as expected for light curves dominated by unstructured white noise. Of the 74 Taurus members/candidates with TrES light curves, we detect significant variability in 49 sources. Adapting a quantitative metric originally developed to assess the reliability of transit detections, we measure the amount of red and white noise in each light curve and identify 18 known or candidate Taurus members with highly significant period measurements. These appear to be the first periods measured for four of these sources (HD 282276, CX Tau, FP Tau, TrES J042423+265008), and in two other cases, the first non-aliased periods (LkCa 21 and DK Tau AB). For the remainder, the TrES measurements typically agree very well (δP < 1%) with previously reported values. Including periods measured at lower confidence for 15 additional sources, we report periods for 11 objects where no previous periods were found, including 8 confirmed Taurus members. We also identify 10 of the 26 candidate Taurus members that demonstrate variability levels consistent with being bona fide T Tauri stars. A Kolomgorov-Smirnov (K-S) test confirms that these new periods confirm the distinction between the rotation period distributions of stars with and without circumstellar

  8. [Astrophysics of binary stars, Seyfert galaxies, quasars, and globular clusters. Final technical report

    International Nuclear Information System (INIS)

    Press, W.H.

    1985-01-01

    Several problems were investigated. The time-steady accretion of gas irradiated by a self-consistently generated quasar-like continuum was studied. The observed x-ray sources near the core of the Orion molecular cloud were established to be sufficient to supply all the ionization that is needed to drive the molecular chemistry throughout that portion of the cloud in which the greatest density and diversity of molecular species is found. A new suggestion was put forth for a single pass, high gain, O 5+ ion laboratory laser at 1035 A. The only evidence for binaries in globular clusters was found to come from binaries in extreme states, cataclysmic variables, and x-ray sources. The various evolutionary paths possible for highly compact binaries in globular clusters where they come under the simultaneous influence of gravitational radiation and gravitational encounters with field stars were analyzed. The secular evolution of a highly compact binary stellar system, composed of a collapsed object and a low-mass secondary star, in the core of a globular cluster was calculated. The dynamics of the narrow line regions of Seyfert galaxies were investigated. New calculations of the soft x-ray opacity of gas having cosmic elemental abunances were developed for a variety of ionization states. Results were presented of the analysis of 28 Einstein SSS observations of 15 high x-ray luminosity quasars and Seyfert type I nuclei

  9. Formation and Evolution of Binary Systems Containing Collapsed Stars

    Science.gov (United States)

    Rappaport, Saul; West, Donald (Technical Monitor)

    2003-01-01

    This research includes theoretical studies of the formation and evolution of five types of interacting binary systems. Our main focus has been on developing a number of comprehensive population synthesis codes to study the following types of binary systems: (i) cataclysmic variables (#3, #8, #12, #15), (ii) low- and intermediate-mass X-ray binaries (#13, #20, #21), (iii) high-mass X-ray binaries (#14, #17, #22), (iv) recycled binary millisecond pulsars in globular clusters (#5, #10, #ll), and (v) planetary nebulae which form in interacting binaries (#6, #9). The numbers in parentheses refer to papers published or in preparation that are listed in this paper. These codes take a new unified approach to population synthesis studies. The first step involves a Monte Carlo selection of the primordial binaries, including the constituent masses, and orbital separations and eccentricities. Next, a variety of analytic methods are used to evolve the primary star to the point where either a dynamical episode of mass transfer to the secondary occurs (the common envelope phase), or the system evolves down an alternate path. If the residual core of the primary is greater than 2.5 solar mass, it will evolve to Fe core collapse and the production of a neutron star and a supernova explosion. In the case of systems involving neutron stars, a kick velocity is chosen randomly from an appropriate distribution and added to the orbital dynamics which determine the state of the binary system after the supernova explosion. In the third step, all binaries which commence stable mass transfer from the donor star (the original secondary in the binary system) to the compact object, are followed with a detailed binary evolution code. Finally, we include all the relevant dynamics of the binary system. For example, in the case of LMXBs, the binary system, with its recoil velocity from the supernova explosion, is followed in time through its path in the Galactic potential. For our globular cluster

  10. JHK photometric study of the variable interstellar extinction in the direction of open star cluster NGC 654

    International Nuclear Information System (INIS)

    Sagar, Ram; Qianzhong Yu

    1989-01-01

    JHK magnitudes have been determined for 18 stars in the field of NGC 654. Study of the interstellar extinction law in the cluster direction indicates an anomalous distribution of interstellar grains causing more extinction in U and B pass-bands compared to that obtained from the colour excesses E(V-J), E(V-H) and E(V-K) using a normal reddening law. This implies a small shift in the grain-size distribution towards smaller than normal sized particles. Patchy distribution of interstellar matter seems to be responsible for the non-uniform extinction in the cluster region. (author)

  11. High-resolution TNG spectra of T Tauri stars. Near-IR GIANO observations of the young variables XZ Tauri and DR Tauri

    Science.gov (United States)

    Antoniucci, S.; Nisini, B.; Biazzo, K.; Giannini, T.; Lorenzetti, D.; Sanna, N.; Harutyunyan, A.; Origlia, L.; Oliva, E.

    2017-10-01

    Aims: We aim to characterise the star-disk interaction region in T Tauri stars that show photometric and spectroscopic variability. Methods: We used the GIANO instrument at the Telescopio Nazionale Galileo to obtain near-infrared high-resolution spectra (R 50 000) of XZ Tau and DR Tau, which are two actively accreting T Tauri stars classified as EXors. Equivalent widths and profiles of the observed features are used to derive information on the properties of the inner disk, the accretion columns, and the winds. Results: Both sources display composite H I line profiles, where contributions from both accreting gas and high-velocity winds can be recognised. These lines are progressively more symmetric and narrower with increasing upper energy which may be interpreted in terms of two components with different decrements or imputed to self-absorption effects. XZ Tau is observed in a relatively high state of activity with respect to literature observations. The variation of the He I 1.08 μm line blue-shifted absorption, in particular, suggests that the inner wind has undergone a dramatic change in its velocity structure, connected with a recent accretion event. DR Tau has a more stable wind as its He I 1.08 μm absorption does not show variations with time in spite of strong variability of the emission component. The IR veiling in the two sources can be interpreted as due to blackbody emission at temperatures of 1600 K and 2300 K for XZ Tau and DR Tau, respectively, with emitting areas 30 times larger than the central star. While for XZ Tau these conditions are consistent with emission from the inner rim of the dusty disk, the fairly high temperature inferred for DR Tau might suggest that its veiling originates from a thick gaseous disk located within the dust sublimation radius. Strong and broad metallic lines, mainly from C I and Fe I, are detected in XZ Tau, similar to those observed in other EXor sources during burst phases. At variance, DR Tau shows weaker and

  12. Slowly pulsating B stars

    Science.gov (United States)

    Waelkens, C.

    1991-06-01

    Photometric data obtained during several years of observations of seven B-type stars are analyzed, including HD 74195 (Omicron Velorum), HD 74560 (HD 3467), HD 123515 (HR 5296), HD 143309, HD 160124, HD 177863 (HR 7241), and HD 181558 (HR 7339). Results indicate that all seven stars are multiperiodic variables with periods of the order of days. Two periods were identified for HD 177863, three periods for HD 74560 and HD 181558, four periods for HD 123515, five periods for HD 74195, six periods for HD 143309, and eight periods for HD 160124. The multiperiodicity and the amplitude behavior of these stars point toward pulsation in high-radial-order g-modes in the stars. It is suggested that these stars form a distinct group of early-type variables, which are named here 'slowly pulsating B stars'.

  13. Paleomagnetism of Early and Middle Pleistocene Cataclysmic Flood Deposits in the Pacific Northwest

    Science.gov (United States)

    Pluhar, C. J.; Burns, S. F.; Carpenter, B.; Yazzie, K.; Melton, D.

    2014-12-01

    Evidence is growing that cataclysmic floods, such as jokulhlaups, have scoured parts of the Pacific Northwest not only during the last glacial maximum (such as the Missoula Floods), but also during earlier parts of the Quaternary. These floods left large erosional features in the "Channeled Scablands" such as colossal flood gravel bars, as well as sediments deposited in backflooded tributary valleys. Evidence for pre-last-glacial cataclysmic floods in the region includes very-well-developed paleosols capping flood deposits, middle Pleistocene U-series disequilibrium dates on some flood sediments, and reversed-paleomagnetic-polarity flood sediments, indicating early Pleistocene age. We document additional evidence for ancient cataclysmic floods at two site, near The Dalles, OR and Othello, WA. The Dalles site consists of 8 flood sediment - capping Stage I to III calcic paleosol couplets, with the third unit from the top containing tephra of the Dibekulewe volcanic ash (0.5 Ma). The sandy nature of the proposed flood sediments is too coarse-grained to attribute to aeolian transport. The Othello site consists of 2 meters of caliche over 40 cm of ancient flood sands and fine gravels We collected paleomagnetic samples from both sites, conducting low temperature cycling (LT), alternating field (AF), and thermal demagnetization experiments on them. These experiments indicate that most samples contain: 1) a large magnetization component in multi-domain magnetite (demagnetized by LT), 2) a large component in goethite (demagnetized by 150°C), and 3) a primary magnetization in pseudo-single and single domain magnetite. The Dalles site spans the Matuyama-Brunhes reversal (0.78 Ma). These and previously published data indicate that one or more mechanisms for generating cataclysmic floods have existed in the Pacific Northwest for much of the Quaternary.

  14. Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae

    Science.gov (United States)

    Patterson, Joseph; Thorstensen, John R.; Kemp, Jonathan; Skillman, David R.; Vanmunster, Tonny; Harvey, David A.; Fried, Robert A.; Jensen, Lasse; Cook, Lewis M.; Rea, Robert; Monard, Berto; McCormick, Jennie; Velthuis, Fred; Walker, Stan; Martin, Brian; Bolt, Greg; Pavlenko, Elena; O'Donoghue, Darragh; Gunn, Jerry; Novák, Rudolf; Masi, Gianluca; Garradd, Gordon; Butterworth, Neil; Krajci, Thomas; Foote, Jerry; Beshore, Edward

    2003-11-01

    We report precise measures of the orbital and superhump period in 20 more dwarf novae. For 10 stars, we report new and confirmed spectroscopic periods-signifying the orbital period Po-as well as the superhump period Psh. These are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS UMa, TU Crt, QW Ser, and RZ Sge. For the remaining 10, we report a medley of Po and Psh measurements from photometry; most are new, with some confirmations of previous values. These are KV And, LL And, WX Cet, MM Hya, AO Oct, V2051 Oph, NY Ser, KK Tel, HV Vir, and RX J1155.4-5641. Periods, as usual, can be measured to high accuracy, and these are of special interest since they carry dynamical information about the binary. We still have not quite learned how to read the music, but a few things are clear. The fractional superhump excess ɛ[=(Psh-Po)/Po] varies smoothly with Po. The scatter of the points about that smooth curve is quite low, and can be used to limit the intrinsic scatter in M1, the white dwarf mass, and the mass-radius relation of the secondary. The dispersion in M1 does not exceed 24%, and the secondary-star radii scatter by no more than 11% from a fixed mass-radius relation. For the well-behaved part of ɛ(Po) space, we estimate from superhump theory that the secondaries are 18%+/-6% larger than theoretical ZAMS stars. This affects some other testable predictions about the secondaries: at a fixed Po, it suggests that the secondaries are (compared with ZAMS predictions) 40%+/-14% less massive, 12%+/-4% smaller, 19%+/-6% cooler, and less luminous by a factor of 2.5(7). The presence of a well-defined mass-radius relation, reflected in a well-defined ɛ(Po) relation, strongly limits effects of nuclear evolution in the secondaries.

  15. Multi-technique investigation of the binary fraction of A-F type candidate hybrid variable stars discovered by Kepler

    Science.gov (United States)

    Lampens, P.; Frémat, Y.; Vermeylen, L.; Sódor, Á.; Skarka, M.; De Cat, P.; Bognár, Zs.; De Nutte, R.; Dumortier, L.; Escorza, A.; Oomen, G. M.; Van de Steene, G.; Kamath, D.; Laverick, M.; Samadi, A.; Triana, S.; Lehmann, H.

    2018-02-01

    Context. Hundreds of candidate hybrid pulsators of intermediate type A-F were revealed by recent space missions. Hybrid pulsators allow us to study the full stellar interiors, where both low-order p- and high-order g-modes are simultaneously excited. The true hybrid stars must be identified since other processes, related to stellar multiplicity or rotation, might explain the presence of (some) low frequencies observed in their periodograms. Aims: We measured the radial velocities of 50 candidate δ Scuti -γ Doradus hybrid stars from the Kepler mission with the Hermes and ACE spectrographs over a time span of months to years. We aim to derive the fraction of binary and multiple systems and to provide an independent and homogeneous determination of the atmospheric properties and v sin i for all targets. The long(er)-term objective is to identify the (probable) physical cause of the low frequencies. Methods: We computed one-dimensional cross-correlation functions (CCFs) in order to find the best set of parameters in terms of the number of components, spectral type(s), and v sin i for each target. Radial velocities were measured using spectrum synthesis and a two-dimensional cross-correlation technique in the case of double- and triple-lined systems. Fundamental parameters were determined by fitting (composite) synthetic spectra to the normalised median spectra corrected for the appropriate Doppler shifts. Results: We report on the analysis of 478 high-resolution Hermes and 41 ACE spectra of A/F-type candidate hybrid pulsators from the Kepler field. We determined their radial velocities, projected rotational velocities, and atmospheric properties and classified our targets based on the shape of the CCFs and the temporal behaviour of the radial velocities. We derived orbital solutions for seven new systems. Three preliminary long-period orbital solutions are confirmed by a photometric time-delay analysis. Finally, we determined a global multiplicity fraction of 27% in

  16. Variability of Disk Emission in Pre-main-sequence and Related Stars. IV. Investigating the Structural Changes in the Inner Disk Region of MWC 480

    Science.gov (United States)

    Fernandes, Rachel B.; Long, Zachary C.; Pikhartova, Monika; Sitko, Michael L.; Grady, Carol A.; Russell, Ray W.; Luria, David M.; Tyler, Dakotah B.; Bayyari, Ammar; Danchi, William; Wisniewski, John P.

    2018-04-01

    We present five epochs of near-IR observations of the protoplanetary disk around MWC 480 (HD 31648) obtained with the SpeX spectrograph on NASA’s Infrared Telescope Facility between 2007 and 2013, inclusive. Using the measured line fluxes in the Pa β and Br γ lines, we found the mass accretion rates to be (1.26–2.30) × 10‑7 M ⊙ yr‑1 and (1.4–2.01) × 10‑7 M ⊙ yr‑1, respectively, but which varied by more than 50% from epoch to epoch. The spectral energy distribution reveals a variability of about 30% between 1.5 and 10 μm during this same period of time. We investigated the variability using of the continuum emission of the disk in using the Monte-Carlo Radiative Transfer Code HOCHUNK3D. We find that varying the height of the inner rim successfully produces a change in the NIR flux but lowers the far-IR emission to levels below all measured fluxes. Because the star exhibits bipolar flows, we utilized a structure that simulates an inner disk wind to model the variability in the near-IR, without producing flux levels in the far-IR that are inconsistent with existing data. For this object, variable near-IR emission due to such an outflow is more consistent with the data than changing the scale height of the inner rim of the disk.

  17. A PSF-based approach to Kepler/K2 data - I. Variability within the K2 Campaign 0 star clusters M 35 and NGC 2158

    Science.gov (United States)

    Libralato, M.; Bedin, L. R.; Nardiello, D.; Piotto, G.

    2016-02-01

    Kepler and K2 data analysis reported in the literature is mostly based on aperture photometry. Because of Kepler's large, undersampled pixels and the presence of nearby sources, aperture photometry is not always the ideal way to obtain high-precision photometry, and, because of this, the data set has not been fully exploited so far. We present a new method that builds on our experience with undersampled HST images. The method involves a point-spread function (PSF) neighbour-subtraction and was specifically developed to exploit the huge potential offered by the K2 `super-stamps' covering the core of dense star clusters. Our test-bed targets were the NGC 2158 and M 35 regions observed during the K2 Campaign 0. We present our PSF modelling and demonstrate that, by using a high-angular-resolution input star list from the Asiago Schmidt telescope as the basis for PSF neighbour subtraction, we are able to reach magnitudes as faint as KP ≃ 24 with a photometric precision of 10 per cent over 6.5 h, even in the densest regions. At the bright end, our photometric precision reaches ˜30 parts per million. Our method leads to a considerable level of improvement at the faint magnitudes (KP ≳ 15.5) with respect to the classical aperture photometry. This improvement is more significant in crowded regions. We also extracted raw light curves of ˜60 000 stars and detrended them for systematic effects induced by spacecraft motion and other artefacts that harms K2 photometric precision. We present a list of 2133 variables.

  18. Non-contrast-enhanced 4D MR angiography with STAR spin labeling and variable flip angle sampling: a feasibility study for the assessment of Dural Arteriovenous Fistula

    International Nuclear Information System (INIS)

    Jang, Jinhee; Kim, Bom-yi; Choi, Hyun Seok; Jung, So-Lyung; Ahn, Kook-Jin; Kim, Bum-soo; Schmitt, Peter; Kim, Inseong; Paek, Munyoung

    2014-01-01

    This study aimed to evaluate the feasibility of non-contrast-enhanced 4D magnetic resonance angiography (NCE 4D MRA) with signal targeting with alternative radiofrequency (STAR) spin labeling and variable flip angle (VFA) sampling in the assessment of dural arteriovenous fistula (DAVF) in the transverse sinus. Nine patients underwent NCE 4D MRA for the evaluation of DAVF in the transverse sinus at 3 T. One patient was examined twice, once before and once after the interventional treatment. All patients also underwent digital subtraction angiography (DSA) and/or contrast-enhanced magnetic resonance angiography (CEMRA). For the acquisition of NCE 4D MRA, a STAR spin tagging method was used, and a VFA sampling was applied in the data readout module instead of a constant flip angle. Two readers evaluated the NCE 4D MRA data for the diagnosis of DAVF and its type with consensus. The results were compared with those from DSA and/or CEMRA. All patients underwent NCE 4D MRA without any difficulty. Among seven patients with patent DAVFs, all cases showed an early visualization of the transverse sinus on NCE 4D MRA. Except for one case, the type of DAVF of NCE 4D MRA was agreed with that of reference standard study. Cortical venous reflux (CVR) was demonstrated in two cases out of three patients with CVR. NCE 4D MRA with STAR tagging and VFA sampling is technically and clinically feasible and represents a promising technique for assessment of DAVF in the transverse sinus. Further technical developments should aim at improvements of spatial and temporal coverage. (orig.)

  19. A new method for studying the thermospheric density variability derived from CHAMP/STAR accelerometer data for magnetically active conditions

    Directory of Open Access Journals (Sweden)

    M. Menvielle

    2007-10-01

    Full Text Available Thermospheric densities deduced from STAR accelerometer measurements onboard the CHAMP satellite are used to characterize the thermosphere and its response to space weather events. The STAR thermospheric density estimates are analysed using a Singular Value Decomposition (SVD approach allowing one to decouple large scale spatial and temporal variations from fast and local transients. Because SVD achieves such decomposition by using the reproducibility of orbital variations, it provides more meaningful results than any method based upon data smoothing or filtering.

    SVD analysis enables us to propose a new thermosphere proxy, based on the projection coefficient of the CHAMP densities on the first singular vector. The large scale spatial variations in the density, mostly related to altitude/latitude variations are captured by the first singular vector; time variations are captured by the associated projection coefficient.

    The study presented here is focused on time dependent global scale variations in the thermospheric density between 50 N and 50 S geographic latitudes. We show that the time variations in the projection coefficient do in fact represent those in the global density that are associated with magnetic activity as well as with solar EUV radiations. We also show that the NRLMSISE-00 empirical model better accounts for the density forcing by Solar radiations when tuned using Mg II indices. Using the so modified model with an additional geomagnetic parameterization corresponding to quiet geomagnetic situation enables one to define time reference values which are then used to evaluate the impact of geomagnetic activity. The ratio of CHAMP density projection coefficient to the quiet model projection coefficient is a global quantity, independent of altitude and latitude, which quantifies the thermospheric density response to auroral energy deposition. It will serve as a proxy of the response of thermospheric density to

  20. 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.

  1. The impact of authentic science inquiry experiences studying variable stars on high school students' knowledge and attitudes about science and astronomy and beliefs regarding the nature of science

    Science.gov (United States)

    Richwine, Pebble Lea

    The purpose of this concurrent mixed methods study was to investigate the impact on high school students' knowledge and attitudes regarding astronomy and beliefs about the nature of science after participating in an extended authentic, inquiry-oriented, research experience studying variable stars using a specifically designed curriculum guide "In the Hunt for Variable Stars." The study gathered quantitative data using a pretest posttest strategy on a modified form of an existing questionnaire called Students Attitudes Toward Astronomy and four student-supplied response content surveys. Qualitative methods included analysis of researcher's field notes, naturalistic observations, formal interviews, and students' artifacts. The methods and results of this study provided important baseline information to measure cognitive and affective changes resulting from an authentic scientific research experience for high school students. Ninety students participated in a targeted instructional sequence and their attitudes and knowledge were compared to 50 students in a comparable science course who were not provided an authentic research experience. The results obtained in this study strongly suggest that participation in research is successful at significantly increasing content knowledge. All four content surveys showed statistically significant increases for students in the intervention group as compared to the students in the non-intervention group. Qualitative results demonstrated that both groups of students initially held naive ideas about science and astronomy. After participation in the intervention, the most dramatic changes were observed in students' understanding of astronomy content. No substantial change was seen in students' attitudes toward Astronomy and science but there is evidence of some limited impacts on beliefs regarding the nature of science. In combination, the data resulting from this mixed-method study lend considerable weight to claim in contemporary

  2. NuSTAR detection of high-energy X-ray emission and rapid variability from sagittarius A* flares

    DEFF Research Database (Denmark)

    Barrière, Nicolas M.; Tomsick, John A.; Baganoff, Frederick K.

    2014-01-01

    Sagittarius A* harbors the supermassive black hole that lies at the dynamical center of our Galaxy. Sagittarius A* spends most of its time in a low luminosity emission state but flares frequently in the infrared and X-ray, increasing up to a few hundred fold in brightness for up to a few hours...... at a time. The physical processes giving rise to the X-ray flares are uncertain. Here we report the detection with the NuSTAR observatory in Summer and Fall 2012 of four low to medium amplitude X-ray flares to energies up to 79 keV. For the first time, we clearly see that the power-law spectrum...... of the two brightest flares (∼55 times quiescence in the 2-10 keV band) are compared to simple physical models in an attempt to identify the main X-ray emission mechanism, but the data do not allow us to significantly discriminate between them. However, we confirm the previous finding that the parameters...

  3. The Rhythm of Fairall 9. I. Observing the Spectral Variability with XMM-Newton and NuSTAR

    DEFF Research Database (Denmark)

    Lohfink, A. M.; Reynolds, C. S.; Pinto, C.

    2016-01-01

    We present a multi-epoch X-ray spectral analysis of the Seyfert 1 galaxy Fairall 9. Our analysis shows that Fairall 9 displays unique spectral variability in that its ratio residuals to a simple absorbed power law in the 0.5–10 keV band remain constant with time in spite of large variations in flux...

  4. High p physics at STAR

    Indian Academy of Sciences (India)

    sub sub

    physics pp. 933–944. High p. T physics at STAR. SUBHASIS CHATTOPADHYAY, for the STAR Collaboration. Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700 064, India. Abstract. We discuss the capabilities of STAR in exploring the physics at high pT in ultrarelativis- tic heavy-ion colisions from RHIC at.

  5. Workshop on The Golden Age of Cataclysmic Variables and Related Objects - II .

    Directory of Open Access Journals (Sweden)

    Editorial, Foreword

    2015-02-01

    Full Text Available Organizing Institutions:INAF – Istituto di Astrofisica e Planetologia Spaziali, Roma – INAF-IAPS, Roma, ItalyINTA – Dpt. de Cargas Utiles y Ciencias del Espacio, INTA-DCUCE, Madrid, SpainCzech Republic Academy of Sciences – Astronomical Institute, ASCR-AI, Ondřejov, Czech RepublicCzech Technical University, CTU in Prague, Czech RepublicDepartment of Physics, Technion, Haifa, IsraelRussian Academy of Sciences – Institute of Astronomy, RAS-IA, Moscow, RussiaINAF - Osservatorio Astronomico di Capodimonte, INAF-OAC, Napoli, ItalyDepartment of Astronomy, University of Washington, Seattle, WA, USA

  6. The ultraviolet pulsations of the cataclysmic variable AE Aquarii as observed with the Hubble Space Telescope

    Science.gov (United States)

    Eracleous, Michael; Horne, Keith; Robinson, Edward L.; Zhang, Er-Ho; Marsh, Thomas R.; Wood, Janet H.

    1994-01-01

    We present the results of high time resolution UV spectroscopy and simultaneous high-speed UBVR photometry of AE Aqr. The UV spectra were obtained with the Faint Object Spectrograph aboard the Hubble Space Telescope (HST), and the photometry was carried out with the 82 sec telescope at McDonald Observatory. Our study focuses on the coherent 33 sceond oscillations, whose amplitude is found to be very large in the UV (40% of the mean quiescent level). The mean pulse profile has two broad unequal peaks spaced by half an oscillation cycle. The pulse profiles in the UV and optical bands appear quite similar in shape, with no discernible shifts. The orbital delay curve of the UV pulses establishes the white dwarf as their origin. The (UV+optical) spectrum of the pulsations is well described by a white dwarf atmosphere model with a temperature of about 26,000 K. We find no oscillations in the UV emission-line fluxes, nor in their velocities, down to a limit of 800 km/s. Based on the properties of the UV and optical pulsations we suggest that they originate in the X-ray heated magnetic polar caps of the white dwarf. Under this assumption we produce maximum entropy maps of the brightness distribution of the white dwarf surface. Using this model we are able to reproduce the observed mean pulse profile and interpret fluctuations in the oscillation amplitude as small fluctuations in the accretion rate. We find that the amplitudes and profiles of the pulses are not strongly affectd by the large aperiodic flares exhibited by the system. This suggests that the large flares are not related to the process of depositing material onto the white dwarf and argues against models that place their origin at the white dwarf magnetosphere.

  7. Discovery of an old nova shell surrounding the cataclysmic variable V1315 Aql

    Science.gov (United States)

    Sahman, D. I.; Dhillon, V. S.; Littlefair, S. P.; Hallinan, G.

    2018-04-01

    Following our tentative discovery of a faint shell around V1315 Aql reported in Sahman et al. (2015), we undertook deep Hα imaging and intermediate-resolution spectroscopy of the shell. We find that the shell has its geometric centre located on V1315 Aql. The mass, spectral features and density of the shell are consistent with other nova shells, rather than planetary nebulae or supernova remnants. The radial velocity of the shell is consistent with the systemic velocity of V1315 Aql. We believe this evidence strongly suggests that the shell originates from an earlier nova event. This is the first nova shell discovered around a novalike, and supports the theory of nova-induced cycles in mass transfer rates (hibernation theory) first proposed by Shara et al. (1986).

  8. Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Nova-Like Cataclysmic Variable BB Doradus

    National Research Council Canada - National Science Library

    Godon, Patrick; Sion, Edward M; Barrett, Paul E; Szkody, Paula; Schlegel, Eric M

    2008-01-01

    ... (possibly lower than 10 ). Assuming an average white dwarf (WD) mass of 0.8 M leads to a mass accretion rate of 10 9 M yr 1 and a distance on the order of 650 pc, consistent with the extremely low Galactic reddening in the direction of BB Dor...

  9. Accretion disk of the cataclysmic variable IY UMa in quiescence and its active state

    Science.gov (United States)

    Khruzina, T. S.; Katysheva, N. A.; Shugarov, S. Yu.

    2008-10-01

    We present the results of a study of the eclipsing binary IY UMa (type SU UMa) during its superoutburst of 2004 and in quiescence.We have refined the orbital period of the system. Light curves are presented for various states of activity.We estimate the parameters of IYUMa during the superoutburst and in quiescence for hot-line and spiral-wave models. The spiral-wave model, which takes into account the presence of vertical perturbations in outer parts of the disk, is able to reproduce the light-curve shapes and phases of dips in the out-of-eclipse parts of the binary’s light curves during the outburst both qualitatively and quantitatively.

  10. The Compton hump and variable blue wing in the extreme low-flux NuSTAR observations of 1H0707-495

    DEFF Research Database (Denmark)

    Kara, E.; Fabian, A. C.; Lohfink, A. M.

    2015-01-01

    of a deep 250-ks NuSTAR (Nuclear Spectroscopic Telescope Array) observation of 1H0707-495, which includes the first sensitive observations above 10 keV. Even though the NuSTAR observations caught the source in an extreme low-flux state, the Compton hump is still significantly detected. NuSTAR, with its high...

  11. Extra-galactic Distances with Massive Stars: The Role of Stellar Variability in the Case of M33

    Energy Technology Data Exchange (ETDEWEB)

    Lee Chien-Hsiu, E-mail: leech@naoj.org [Subaru Telescope, NAOJ, 650 N Aohoku Pl, Hilo, HI 96720 (United States)

    2017-08-01

    In modern cosmology, determining the Hubble constant (H{sub 0}) using a distance ladder to percent level and comparing with the results from the Planck  satellite can shed light on the nature of dark energy, physics of the neutrino, and curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H{sub 0} has be dramatically reduced, from 10% to 2.4%, and with the promise of even reaching 1% in the near future. In this regard, it is fundamentally important to investigate the systematics. This is best done using other good independent distance indicators. One promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants (BSGs). As BSGs are the brightest objects in galaxies, they can probe distances up to 10 Mpc with negligible blending effects. While the FGLR method delivered distance is in good agreement with other distance indicators, it has been shown that this method delivers greater distances in the cases of M33 and NGC 55. Here, we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found that 9 out of 22 BSGs showed variability during the course of 500 days, although with amplitudes as small as 0.05 mag. This suggests that stellar variability plays a negligible role in the FGLR distance determination.

  12. Extra-galactic Distances with Massive Stars: The Role of Stellar Variability in the Case of M33

    Science.gov (United States)

    Lee, Chien-Hsiu

    2017-08-01

    In modern cosmology, determining the Hubble constant (H0) using a distance ladder to percent level and comparing with the results from the Planck satellite can shed light on the nature of dark energy, physics of the neutrino, and curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H0 has be dramatically reduced, from 10% to 2.4%, and with the promise of even reaching 1% in the near future. In this regard, it is fundamentally important to investigate the systematics. This is best done using other good independent distance indicators. One promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants (BSGs). As BSGs are the brightest objects in galaxies, they can probe distances up to 10 Mpc with negligible blending effects. While the FGLR method delivered distance is in good agreement with other distance indicators, it has been shown that this method delivers greater distances in the cases of M33 and NGC 55. Here, we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found that 9 out of 22 BSGs showed variability during the course of 500 days, although with amplitudes as small as 0.05 mag. This suggests that stellar variability plays a negligible role in the FGLR distance determination.

  13. Growth, reproduction and possible recruitment variability in the abyssal brittle star Ophiocten hastatum (Ophiuroidea: Echinodermata) in the NE Atlantic

    Science.gov (United States)

    Gage, John D.; Anderson, Roslyn M.; Tyler, Paul A.; Chapman, Rachel; Dolan, Emily

    2004-06-01

    Growth was studied from skeletal growth markers in the cosmopolitan abyssal brittle star Ophiocten hastatm. Samples for analysis were taken at five sites located in the southern (2900 m) and central (2000 m) Rockall Trough, at ca. 3000 and 4000 m in the Porcupine Seabight, and at 4850 m on the Porcupine Abyssal Plain. Growth bands were assumed to reflect an annual cycle in skeletal growth. Band measurements on arm vertebrae, standardised to disc diameter, were used to provide size-at-age data and size-increment data that took into account overgrowth of early bands in older individuals. The Richards growth function marginally provides best fit to pooled size-at-age data, although the asymptote-less Tanaka function and the Gompertz growth function also provided good fit to size-at-age data which showed a rather linear growth pattern with little indication of a growth asymptote. Log e transformed size-increment data were linearised by applying the Ford-Walford method to approximate Gompertz growth so that growth could be compared at the five sites. Grouped linear regression and analysis of covariance showed no significant differences between growth at the sites and a common fitted regression. However, pairwise comparisons suggest growth differences with increasing bathymetric separation. Oocyte size frequencies measured from histological preparations of the gonad of specimens from the Porcupine Abyssal Plain indicate marked reproductive periodicity, with spawn-out in late winter that is likely followed by planktotrophic early development in spring with benthic settlement in summer. Although usually rare in the trawl and epibenthic sled samples, several years of successful recruitment followed by a period when recruitment was low or absent might explain size structure observed in a single unusually large sample from the Rockall Trough. This is consistent with previous observations during the late 1990s of a large population increase on the Porcupine Abyssal Plain

  14. An extremely luminous and variable ultraluminous x-ray source in the outskirts of circinus observed with NuSTAR

    DEFF Research Database (Denmark)

    Walton, D. J.; Fuerst, F.; Harrison, F.

    2013-01-01

    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 proportional to T1.70+/-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...

  15. The Distance to M54 using Infrared Photometry of RR Lyrae Variable Stars and the Implications of its Relation to the Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Gupta, Arvind F.; Beaton, Rachael L.; Majewski, Steven R.; SMHASH Team

    2018-01-01

    CDM cosmological models predict that dark matter halo density profiles will have central cusps. Yet for many dwarf spheroidal galaxies (dSphs), this expectation is in contrast with observations of cored, rather than cusped, halos. This 'cusp-core problem' is apparent in the Sagittarius Dwarf Galaxy (Sgr), one of the largest satellites of the Milky Way. The globular cluster M54, one of several clusters associated with Sgr, coincides in on-sky position with the center of the main body of Sgr. While several studies find that M54 lies within the center of Sgr, other findings show that M54 is offset from the center by several kiloparsecs along our line of sight. The latter requires Sgr to have a cored dark matter distribution. In the presence of a cuspy halo, the orbit of M54 would have decayed via dynamical friction and the cluster would have fallen to the center of Sgr. A clear determination of the relation of the two bodies may help us better understand the distribution of dark matter in Sgr and other dSphs. Here we present a measurement of the distance modulus to M54 using a set of RR Lyrae variable stars in near-infrared Magellan data mid-infrared Spitzer data. The magnitudes of individual stars are measured using multi-epoch PSF photometry and light curve fitting. From precise RR Lyrae period-luminosity relations at these wavelengths, we then find the mean M54 distance modulus to be 17.126 ± 0.023 (ran) ± 0.080 (sys). Our result is consistent with a distance measurement to Sgr derived via nearly identical methods and thus also consistent with the expectation of a central cusp in the dark matter density profile of Sgr.

  16. Joseph O’Connor. Star of the Sea

    Directory of Open Access Journals (Sweden)

    Alexandra POULAIN

    2007-10-01

    Full Text Available It has become a commonplace to note that although the Irish Famine was a major cataclysm, and one which contributed to the complete reshaping of Ireland in the late nineteenth-century, it has not often found its way into Irish literature – arguably because it was simply too traumatic for representation: as Terry Eagleton puts it, “the events strains at the limits of the inarticulable.” In Star of the Sea, however, the young Irish novelist Joseph O’Connor not only vividly conjures up the memor...

  17. The Onset of the Cataclysm: In Situ Dating of the Nectaris Basin Impact Melt Sheet

    Science.gov (United States)

    Cohen, B. A.

    2017-01-01

    The impact history of the Moon has significant implications beyond simply excavating the surface of our nearest neighbor. The age distribution of lunar impact breccias inspired the idea of a catastrophic influx of asteroids and comets about 4 billion years ago and motivated new models of planetary dynamics. An epoch of heavy bombardment after planets had atmospheres and continents would have influenced the course of biologic evolution. The story of a cataclysmic bombardment, written in the rocks of the Moon, has far-reaching consequences.

  18. NuSTAR AND SWIFT Observations of the Fast Rotating Magnetized White Dwarf AE Aquarii

    Science.gov (United States)

    Kitaguchi, Takao; An, Hongjun; Beloborodov, Andrei M.; Gotthelf, Eric V.; Hayashi, Takayuki; Kaspi, Victoria M.; Rana, Vikram R.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; hide

    2014-01-01

    AE Aquarii is a cataclysmic variable with the fastest known rotating magnetized white dwarf (P(sub spin) = 33.08 s). Compared to many intermediate polars, AE Aquarii shows a soft X-ray spectrum with a very low luminosity (LX (is) approximately 10(exp 31) erg per second). We have analyzed overlapping observations of this system with the NuSTAR and the Swift X-ray observatories in 2012 September. We find the 0.5-30 keV spectra to be well fitted by either an optically thin thermal plasma model with three temperatures of 0.75(+0.18 / -0.45), 2.29(+0.96 / -0.82), and 9.33 (+6.07 / -2.18) keV, or an optically thin thermal plasma model with two temperatures of 1.00 (+0.34 / -0.23) and 4.64 (+1.58 / -0.84) keV plus a power-law component with photon index of 2.50 (+0.17 / -0.23). The pulse profile in the 3-20 keV band is broad and approximately sinusoidal, with a pulsed fraction of 16.6% +/- 2.3%. We do not find any evidence for a previously reported sharp feature in the pulse profile.

  19. 2FGL J0846.0+2820: A New Neutron Star Binary with a Giant Secondary and Variable γ-Ray Emission

    Science.gov (United States)

    Swihart, Samuel J.; Strader, Jay; Johnson, Tyrel J.; Cheung, C. C.; Sand, David; Chomiuk, Laura; Wasserman, Asher; Larsen, Søren; Brodie, Jean P.; Simonian, Gregory V.; Tremou, Evangelia; Shishkovsky, Laura; Reichart, Daniel E.; Haislip, Joshua

    2017-12-01

    We present optical photometric and spectroscopic observations of the likely stellar counterpart to the unassociated Fermi Large Area Telescope (LAT) γ-ray source 2FGL J0846.0+2820, selected for study based on positional coincidences of optical variables with unassociated LAT sources. Using optical spectroscopy from the SOAR telescope, we have identified a late-G giant in an eccentric (e = 0.06) 8.133-day orbit with an invisible primary. Modeling the spectroscopy and photometry together led us to infer a heavy neutron star primary of ˜ 2 {M}⊙ and a partially stripped giant secondary of ˜ 0.8 {M}⊙ . Hα emission is observed in some of the spectra, perhaps consistent with the presence of a faint accretion disk. We find that the γ-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009, accompanied by an increased variation in the optical brightness, and since then, it has not been detected by Fermi. The long period and giant secondary are reminiscent of the γ-ray bright binary 1FGL J1417.7-4407, which hosts a millisecond pulsar (MSP) apparently in the final stages of the pulsar recycling process. The discovery of 2FGL J0846.0+2820 suggests the identification of a new subclass of MSP binaries that are the likely progenitors of typical field MSPs.

  20. Peak flow responses to landscape disturbances caused by the cataclysmic 1980 eruption of Mount St. Helens, Washington

    Science.gov (United States)

    Major, Jon J.; Mark, Linda E.

    2006-01-01

    Years of discharge measurements that precede and follow the cataclysmic 1980 eruption of Mount St. Helens, Washington, provide an exceptional opportunity to examine the responses of peak flows to abrupt, widespread, devastating landscape disturbance. Multiple basins surrounding Mount St. Helens (300–1300 km2 drainage areas) were variously disturbed by: (1) a debris avalanche that buried 60 km2 of valley; (2) a lateral volcanic blast and associated pyroclastic flow that destroyed 550 km2 of mature forest and blanketed the landscape with silt-capped lithic tephra; (3) debris flows that reamed riparian corridors and deposited tens to hundreds of centimeters of gravelly sand on valley floors; and (4) a Plinian tephra fall that blanketed areas proximal to the volcano with up to tens of centimeters of pumiceous silt, sand, and gravel. The spatially complex disturbances produced a variety of potentially compensating effects that interacted with and influenced hydrological responses. Changes to water transfer on hillslopes and to flow storage and routing along channels both enhanced and retarded runoff. Rapid post-eruption modifications of hillslope surface textures, adjustments of channel networks, and vegetation recovery, in conjunction with the complex nature of the eruptive impacts and strong seasonal variability in regional climate hindered a consistent or persistent shift in peak discharges. Overall, we detected a short-lived (5–10 yr) increase in the magnitudes of autumn and winter peak flows. In general, peak flows were larger, and moderate to large flows (>Q2 yr) were more substantively affected than predicted by early modeling efforts. Proportional increases in the magnitudes of both small and large flows in basins subject to severe channel disturbances, but not in basins subject solely to hillslope disturbances, suggest that eruption-induced modifications to flow efficiency along alluvial channels that have very mobile beds differentially affected flows of

  1. Order Amidst Chaos of Star's Explosion

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] Click on the image for movie of Order Amidst Chaos of Star's Explosion This artist's animation shows the explosion of a massive star, the remains of which are named Cassiopeia A. NASA's Spitzer Space Telescope found evidence that the star exploded with some degree of order, preserving chunks of its onion-like layers as it blasted apart. Cassiopeia A is what is known as a supernova remnant. The original star, about 15 to 20 times more massive than our sun, died in a cataclysmic 'supernova' explosion viewable from Earth about 340 years ago. The remnant is located 10,000 light-years away in the constellation Cassiopeia. The movie begins by showing the star before it died, when its layers of elements (shown in different colors) were stacked neatly, with the heaviest at the core and the lightest at the top. The star is then shown blasting to smithereens. Spitzer found evidence that the star's original layers were preserved, flinging outward in all directions, but not at the same speeds. In other words, some chunks of the star sped outward faster than others, as illustrated by the animation. The movie ends with an actual picture of Cassiopeia A taken by Spitzer. The colored layers containing different elements are seen next to each other because they traveled at different speeds. The infrared observatory was able to see the tossed-out layers because they light up upon ramming into a 'reverse' shock wave created in the aftermath of the explosion. When a massive star explodes, it creates two types of shock waves. The forward shock wave darts out quickest, and, in the case of Cassiopeia A, is now traveling at supersonic speeds up to 7,500 kilometers per second (4,600 miles/second). The reverse shock wave is produced when the forward shock wave slams into a shell of surrounding material expelled before the star died. It tags along behind the forward shock wave at slightly slower speeds. Chunks of the star that were thrown out

  2. The Galex Time Domain Survey. I. Selection And Classification of Over a Thousand Ultraviolet Variable Sources

    Science.gov (United States)

    Gezari, S.; Martin, D. C.; Forster, K.; Neill, J. D.; Huber, M.; Heckman, T.; Bianchi, L.; Morrissey, P.; Neff, S. G.; Seibert, M.; hide

    2013-01-01

    We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in approximately 40 deg(exp 2) of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of approximately 3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5 sigma level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). We detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to absolute value(?m) = 4.6 mag and 2.9 mag, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with NUV less than 23 mag and absolute value(?m) greater than 0.2 mag of approximately 8.0, 7.7, and 1.8 deg(exp -2) for quasars, active galactic nuclei, and RR Lyrae stars

  3. Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-variable Horizontal-branch Stars. I. M3, M15, and M92

    Science.gov (United States)

    VandenBerg, Don A.; Denissenkov, P. A.; Catelan, Márcio

    2016-08-01

    Up-to-date isochrones, zero-age horizontal-branch (ZAHB) loci, and evolutionary tracks for core He-burning stars are applied to the color-magnitude diagrams of M3, M15, and M92, focusing in particular on their RR Lyrae populations. Periods for the ab- and c-type variables are calculated using the latest theoretical calibrations of {log} {P}{ab} and {log} {P}c as a function of luminosity, mass, effective temperature ({T}{{eff}}), and metallicity. Our models are generally able to reproduce the measured periods to well within the uncertainties implied by the stellar properties on which pulsation periods depend, as well as the mean periods and cluster-to-cluster differences in and , on the assumption of well-supported values of E(B-V), {(m-M)}V, and [Fe/H]. While many of RR Lyrae in M3 lie close to the same ZAHB that fits the faintest horizontal-branch (HB) stars at bluer or redder colors, the M92 variables are all significantly evolved stars from ZAHB locations on the blue side of the instability strip. M15 appears to contain a similar population of HB stars as M92, along with additional helium-enhanced populations not present in the latter which comprise most of its RR Lyrae stars. The large number of variables in M15 and the similarity of the observed values of and in M15 and M92 can be explained by HB models that allow for variations in Y. Similar ages (˜12.5 Gyr) are found for all three clusters, making them significantly younger than the field halo subgiant HD 140283. Our analysis suggests a preference for stellar models that take diffusive processes into account.

  4. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

  5. THE NuSTAR Hard X-Ray Survey of the Norma Arm Region

    Science.gov (United States)

    Fornasini, Francesca M.; Tomsick, John A.; Hong, Jaesub; Gotthelf, Eric V.; Bauer, Franz; Rahoui, Farid; Stern, Daniel K.; Bodaghee, Arash; Chiu, Jeng-Lun; Clavel, Maïca; hide

    2017-01-01

    We present a catalog of hard X-ray sources in a square-degree region surveyed by the Nuclear Spectroscopic Telescope Array (NuSTAR) in the direction of the Norma spiral arm. This survey has a total exposure time of 1.7 Ms, and the typical and maximum exposure depths are 50 ks and 1 Ms, respectively. In the area of deepest coverage, sensitivity limits of 5 x 10(exp -14) and 4 x 10(exp -14) ergs/s/sq cm in the 3-10 and 10-20 keV bands, respectively, are reached. Twenty-eight sources are firmly detected, and 10 are detected with low significance; 8 of the 38 sources are expected to be active galactic nuclei. The three brightest sources were previously identified as a low-mass X-ray binary, high-mass X-ray binary, and pulsar wind nebula. Based on their X-ray properties and multiwavelength counterparts, we identify the likely nature of the other sources as two colliding wind binaries, three pulsar wind nebulae, a black hole binary, and a plurality of cataclysmic variables (CVs). The CV candidates in the Norma region have plasma temperatures of approx. 10-20 keV, consistent with the Galactic ridge X-ray emission spectrum but lower than the temperatures of CVs near the Galactic center. This temperature difference may indicate that the Norma region has a lower fraction of intermediate polars relative to other types of CVs compared to the Galactic center. The NuSTAR logN-logS distribution in the 10-20keV band is consistent with the distribution measured by Chandra at 2-10 keV if the average source spectrum is assumed to be a thermal model with kT approx. =15 keV, as observed for the CV candidates.

  6. Molecular Star

    Indian Academy of Sciences (India)

    This report describes the making of a self-assembled coordination architecture that is named as a 'molecular star' since it resembles the shape of a star; more specifically a five-pointed star. This work has been already published in Chemistry- A European Jour- nal in the September 2017 issue and was featured in the cover.

  7. VARIABILITY OF DISK EMISSION IN PRE-MAIN SEQUENCE AND RELATED STARS. III. EXPLORING STRUCTURAL CHANGES IN THE PRE-TRANSITIONAL DISK IN HD 169142

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Kevin R.; Sitko, Michael L.; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Werren, Chelsea [Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Whitney, Barbara A. [Department of Astronomy, University of Wisconsin, 475 North CharterStreet, Madison, WI 53706-1582 (United States); Russell, Ray W. [The Aerospace Corporation, Los Angeles, CA 90009 (United States); Schneider, Glenn H. [Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721 (United States); Momose, Munetake [Ibaraki University, 310-0056 Ibaraki, Mito, Bunkyo, 11 (Japan); Muto, Takayuki [Kogakuin University, 1-24-2 Nishishinjuku, Shinjuku, Tokyo 163-8677 (Japan); Inoue, Akio K. [Osaka Sangyo University, College of General Education, 3-1-1 Nakagaito, Daito, Osaka 574-8530 (Japan); Lauroesch, James T.; Hornbeck, Jeremy [University of Louisville Research Foundation, Inc., 2301 South 3rd Street, Louisville, KY 40292 (United States); Brown, Alexander [Center for Astrophysics and Space Astronomy, Astrophysics Research Laboratory, 593 UCB, University of Colorado, Boulder, CO 80309-0593 (United States); Fukagawa, Misato [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Currie, Thayne M. [Oak Ridge Associated Universities, 100 ORAU Way, Oak Ridge, TN 37830-6218 (United States); Wisniewski, John P. [University of Oklahoma, 660 Parrington Oval, Norman, OK 73019 (United States); Woodgate, Bruce E., E-mail: wagnekr@mail.uc.edu, E-mail: sitkoml@ucmail.uc.edu, E-mail: swearijr@mail.uc.edu, E-mail: ehchampney@gmail.com, E-mail: astefank@andrew.cmu.edu, E-mail: ccwerren@yahoo.com, E-mail: carol.a.grady@nasa.gov, E-mail: bwhitney@astro.wisc.edu, E-mail: Ray.W.Russell@aero.org [NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)

    2015-01-10

    We present near-IR (NIR) and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between ∼1.5-10 μm over a maximum timescale of 10 yr. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the ≲1 AU region of the disk. Through analysis of the Pa β and Br γ lines in our data we derive a mass accretion rate in 2013 May of M-dot ≈ (1.5-2.7) × 10{sup –9} M {sub ☉} yr{sup –1}. We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 yr of observations. We find that shifting the outer edge (r ≈ 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ∼40-70 AU dark ring imaged in the NIR by Quanz et al. and Momose et al. and at 7 mm by Osorio et al. may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.

  8. An Ultradeep Chandra Catalog of X-Ray Point Sources in the Galactic Center Star Cluster

    Science.gov (United States)

    Zhu, Zhenlin; Li, Zhiyuan; Morris, Mark R.

    2018-04-01

    We present an updated catalog of X-ray point sources in the inner 500″ (∼20 pc) of the Galactic center (GC), where the nuclear star cluster (NSC) stands, based on a total of ∼4.5 Ms of Chandra observations taken from 1999 September to 2013 April. This ultradeep data set offers unprecedented sensitivity for detecting X-ray sources in the GC, down to an intrinsic 2–10 keV luminosity of 1.0 × 1031 erg s‑1. A total of 3619 sources are detected in the 2–8 keV band, among which ∼3500 are probable GC sources and ∼1300 are new identifications. The GC sources collectively account for ∼20% of the total 2–8 keV flux from the inner 250″ region where detection sensitivity is the greatest. Taking advantage of this unprecedented sample of faint X-ray sources that primarily traces the old stellar populations in the NSC, we revisit global source properties, including long-term variability, cumulative spectra, luminosity function, and spatial distribution. Based on the equivalent width and relative strength of the iron lines, we suggest that in addition to the arguably predominant population of magnetic cataclysmic variables (CVs), nonmagnetic CVs contribute substantially to the detected sources, especially in the lower-luminosity group. On the other hand, the X-ray sources have a radial distribution closely following the stellar mass distribution in the NSC, but much flatter than that of the known X-ray transients, which are presumably low-mass X-ray binaries (LMXBs) caught in outburst. This, together with the very modest long-term variability of the detected sources, strongly suggests that quiescent LMXBs are a minor (less than a few percent) population.

  9. 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.

  10. 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

  11. HIGHLY VARIABLE EXTINCTION AND ACCRETION IN THE JET-DRIVING CLASS I-TYPE YOUNG STAR PTF 10nvg (V2492 Cyg, IRAS 20496+4354)

    Energy Technology Data Exchange (ETDEWEB)

    Hillenbrand, Lynne A.; Carpenter, John M.; Muirhead, Philip S.; Crepp, Justin R. [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Miller, Adam A.; Cenko, S. Bradley; Silverman, Jeffrey M.; Bloom, Joshua S.; Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Covey, Kevin R. [Department of Astronomy, Cornell University, 226 Space Sciences Building, Ithaca, NY 14853 (United States); Fischer, William J. [Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States)

    2013-03-15

    the broad H{alpha} and Ca II triplet emission lines, similarly are formed in the outflow. CARMA maps resolve on larger scales a spatially extended outflow in millimeter-wavelength CO. We attribute the recently observed photometric and spectroscopic behavior to rotating circumstellar disk material located at separation a Almost-Equal-To 0.7(M{sub *}/M{sub Sun }){sup 1/3} AU from the continuum source, causing the semi-periodic dimming. Occultation of the central star as well as the bright inner disk and the accretion/outflow zones renders shocked gas in the inner part of the jet amenable to observation at the faint epochs. We discuss PTF 10nvg as a source exhibiting both accretion-driven (perhaps analogous to V1647 Ori) and extinction-driven (perhaps analogous to UX Ori or GM Cep) high-amplitude variability phenomena.

  12. 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

  13. Chromospheres of Luminous Cool Stars

    Science.gov (United States)

    Dupree, A. K.

    Direct ultraviolet imaging and spectroscopy of Alpha Orionis (Betelgeuse) reveals variable chromospheric structures and mass motions. Spectroscopy also demonstrates the changes of wind opacity, speeds, and mass loss in luminous stars. Cool stars have complex chromospheres that need to be considered in construction of stellar atmospheric models and subsequent spectral analyses.

  14. On the history of the early meteoritic bombardment of the Moon: Was there a terminal lunar cataclysm?

    Science.gov (United States)

    Michael, Greg; Basilevsky, Alexander; Neukum, Gerhard

    2018-03-01

    This work revisits the hypothesis of the so-called 'lunar terminal cataclysm' suggested by Tera et al. (1973, 1974) as a strong peak in the meteorite bombardment of the Moon around 3.9 Ga ago. According to the hypothesis, most of the impact craters observed on the lunar highlands formed during this short time period and thus formed the majority of the lunar highland impact breccias and melts. The hypothesis arose from the observation that the ages of highland samples from all the lunar missions are mostly grouped around 3.9-4.0 Ga. Since those missions, however, radiometric dating techniques have progressed and many samples, both old and new, have been re-analyzed. Nevertheless, the debate over whether there was a terminal cataclysm persists. To progress in this problem we summarized results of 269 K-Ar datings (mostly made using the 40Ar-39Ar technique) of highland rocks represented by the Apollo 14, 15, 16, 17 and Luna 20 samples and 94 datings of clasts of the highland rocks from 23 lunar meteorites representing 21 localities on the lunar surface, and considered them jointly with the results of our modelling of the cumulative effect of the impact gardening process on the presence of impact melt of different ages at the near-surface of the Moon. The considered results of K-Ar dating of the Apollo-Luna samples of lunar highland rocks confirmed a presence of strong peak centered at 3.87 Ga. But since the time when the hypothesis of terminal cataclysm was suggested, it has become clear that this peak could be a result of sampling bias: it is the only prominent feature at the sites with an apparent domination of Imbrium basin ejecta (Apollo 14 and 15) and the age pattern is more complicated for the sites influenced not only by Imbrium ejecta but also that of other basins (Nectaris at the Apollo 16 site and Serenitatis at the Apollo 17 site). Our modelling shows that the cataclysm, if it occurred, should produce a strong peak in the measured age values but we see in

  15. Evolution of stars and galaxies

    International Nuclear Information System (INIS)

    Baade, W.

    1975-01-01

    Transcriptions of recorded lectures given by the author have been edited into book form. Topics covered include: historical introduction, classification of galaxies; observation of galaxies; photography of galaxies; the andromeda nebula, spiral structure; dust and gas in galaxies; outline of stellar evolution; the distances to the galaxies; galactic clusters; stellar associations; the T Tauri stars; globular clusters: color-magnitude diagrams; spectra of population II stars; variable stars in globular clusters; elliptical galaxies; irregular galaxies and star formation; the magellanic clouds; the andromeda nebula, photometry; evolution of galaxies; the structure of the galaxy; the galactic nucleus; the galactic disk; and kinematics and evolution of the galaxy. 27 tables, 26 figures

  16. Interacting binary stars

    International Nuclear Information System (INIS)

    Pringle, J.E.; Wade, R.A.

    1985-01-01

    This book reviews the theoretical and observational knowledge of interacting binary stars. The topics discussed embrace the following features of these objects: their orbits, evolution, mass transfer, angular momentum losses, X-ray emission, eclipses, variability, and other related phenomena. (U.K.)

  17. SN2015bh: NGC2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?

    DEFF Research Database (Denmark)

    Thone, C. C.; de Ugarte Postigo, A.; Leloudas, G.

    2017-01-01

    shell plunging into a dense CSM. The emission lines show a single narrow P Cygni profile during the LBV phase and a double P Cygni profile post maximum suggesting an association of the second component with the possible SN. Since 1994 the star has been redder than an LBV in an S-Dor-like outburst. SN...

  18. The Galactic unclassified B[e] star HD50138 III. The short-term line profile variability of its photospheric lines

    Czech Academy of Sciences Publication Activity Database

    Borges Fernandes, M.; Kraus, Michaela; Nickeler, Dieter Horst; de Cat, P.; Lampens, P.; Pereira, C. A. B.; Oksala, Mary E.

    2012-01-01

    Roč. 548, November (2012), A13/1-A13/9 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GAP209/11/1198 Institutional support: RVO:67985815 Keywords : stars * oscillations * mass-loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  19. The Seyfert 2 galaxy NGC 2110: hard X-ray emission observed by NuSTAR and variability of the iron Kα line

    DEFF Research Database (Denmark)

    Marinucci, A.; Matt, G.; Bianchi, S.

    2015-01-01

    -Newton, Suzaku, BeppoSAX, Chandra and Swift. Simultaneous NuSTAR and Swift broad-band spectra (in the 3-80 keV range) indicate a cutoff energy Ec > 210 keV, with no detectable contribution from Compton reflection. NGC 2110 is one of the very few sources where no evidence for distant Compton-thick scattering...

  20. Cataclysms and Catastrophes: A Case Study of Improving K-12 Science Education Through a University Partnership

    Science.gov (United States)

    Fennell, T.; Ellins, K. K.; Morris, M.; Christeson, G.

    2003-12-01

    The K-12 science teacher is always seeking ways of improving and updating their curriculum by integrating the latest research into their most effective classroom activities. However, the daily demands of delivering instruction to large numbers of students coupled with the rapid advances in some fields of science can often overwhelm this effort. The NSF-sponsored Cataclysms and Catastrophes curriculum, developed by scientists from the The University of Texas at Austin Institute for Geophysics (UTIG) and Bureau of Economic Geology (BEG), middle and high school teachers, and UT graduate students (NSF GK-12 fellows) working together through the GK-12 program, is a textbook example of how universities can facilitate this quest, benefiting education at both K-12 and university levels. In 1992, "The Great K-T Extinction Debate" was developed as an activity in the Planet Earth class at the Liberal Arts and Science Academy of Austin as an interdisciplinary approach to science. Taking advantage of the media attention generated by the impact scenario for the K-T extinction, the activity consists of students participating in a simulated senate hearing on the potential causes of the K-T extinction and their implications for society today. This activity not only exposes students to the wide range of science involved in understanding mass extinctions, but also to the social, political and economic implications when this science is brought into the public arena and the corresponding use of data in decision making and disaster preparedness. While "The Great K-T Extinction Debate" was always a popular and effective activity with students, it was in desperate need of updating to keep pace with the evolving scientific debate over the cause of the K-T extinction and the growing body of impact evidence discovered over the past decade. By adding two inquiry-based learning activities that use real geophysical data collected by scientists studying the buried Chicxulub feature as a

  1. WIND VARIABILITY IN BZ CAMELOPARDALIS

    International Nuclear Information System (INIS)

    Honeycutt, R. K.; Kafka, S.; Robertson, J. W.

    2013-01-01

    Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur frequently in this star. We confirm the results of Ringwald and Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We also commonly find blueshifted emission components in the Hα line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald and Naylor reported common occurrences of redshifted Hα emission components in their BZ Cam spectra. We have attributed these emission components in Hα to occasions when gas concentrations in the bipolar wind (both front side and back side) become manifested as emission lines as they move beyond the disk's outer edge. We also suggest, based on changes in the P-Cygni profiles during an episode, that the progression from larger to smaller expansion velocities is due to the higher velocity portions of a wind concentration moving beyond the edge of the continuum light of the disk first, leaving a net redward shift of the remaining absorption profile. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the He I λ5876 line, finding P = 0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We argue that the radiation-driven wind in BZ Cam receives an initial boost by acting on gas that has been lifted above the disk by the interaction of the accretion stream with the disk, thereby imposing flickering timescales onto the wind events, as well as leading to an orbital modulation of the wind due to the non

  2. 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.

  3. Star Imager

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Jørgensen, John Leif; Thuesen, Gøsta

    1997-01-01

    The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol.......The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol....

  4. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star.......Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star....

  5. Henrietta Leavitt - A Bright Star of Astronomy; Resonance June 2001

    Indian Academy of Sciences (India)

    Leavitt discovered around a thousand variable stars in these clouds. Among these, she found 25. Cepheid variables in the small Magellanic cloud and noted that the period of these variable stars were correlated with the peak brightness. The brighter the star was, the longer it took to vary its brightness. In other words, the.

  6. CSI 2264: simultaneous optical and infrared light curves of young disk-bearing stars in NGC 2264 with CoRoT and Spitzer—evidence for multiple origins of variability

    International Nuclear Information System (INIS)

    Cody, Ann Marie; Stauffer, John; Rebull, Luisa M.; Carey, Sean; Baglin, Annie; Micela, Giuseppina; Flaccomio, Ettore; Morales-Calderón, María; Aigrain, Suzanne; Bouvier, Jèrôme; Hillenbrand, Lynne A.; Carpenter, John; Findeisen, Krzysztof; Gutermuth, Robert; Song, Inseok; Turner, Neal; Alencar, Silvia H. P.; Zwintz, Konstanze; Plavchan, Peter; Terebey, Susan

    2014-01-01

    We present the Coordinated Synoptic Investigation of NGC 2264, a continuous 30 day multi-wavelength photometric monitoring campaign on more than 1000 young cluster members using 16 telescopes. The unprecedented combination of multi-wavelength, high-precision, high-cadence, and long-duration data opens a new window into the time domain behavior of young stellar objects. Here we provide an overview of the observations, focusing on results from Spitzer and CoRoT. The highlight of this work is detailed analysis of 162 classical T Tauri stars for which we can probe optical and mid-infrared flux variations to 1% amplitudes and sub-hour timescales. We present a morphological variability census and then use metrics of periodicity, stochasticity, and symmetry to statistically separate the light curves into seven distinct classes, which we suggest represent different physical processes and geometric effects. We provide distributions of the characteristic timescales and amplitudes and assess the fractional representation within each class. The largest category (>20%) are optical 'dippers' with discrete fading events lasting ∼1-5 days. The degree of correlation between the optical and infrared light curves is positive but weak; notably, the independently assigned optical and infrared morphology classes tend to be different for the same object. Assessment of flux variation behavior with respect to (circum)stellar properties reveals correlations of variability parameters with Hα emission and with effective temperature. Overall, our results point to multiple origins of young star variability, including circumstellar obscuration events, hot spots on the star and/or disk, accretion bursts, and rapid structural changes in the inner disk.

  7. Classical pulsating variables

    International Nuclear Information System (INIS)

    Hacke, G.

    1987-01-01

    The nature of the three types of classical pulsating variables (δ-Cephei stars, W-Virginis stars and RR-Lyrae stars) is studied. Problems of the light-curve analysis such as (1) the frequency distribution of periods for the three types of classical pulsating variables, (2) spurions periods, (3) changes of periods and multiple periodicity as well as (4) the Blazhko-effect and other changes of the light-curve form are discussed

  8. Accurate and Autonomous Star Acquisition Method for Star Sensor under Complex Conditions

    Directory of Open Access Journals (Sweden)

    Hao Zhang

    2017-01-01

    Full Text Available Star sensor is a preferred attitude measurement device for its extremely high accuracy. Star acquisition is the essential and critical procedure, which is aiming at acquiring accurate star areas. However, degenerated acquisition results under complex conditions become one of the major restrictions for modern star sensor. In this paper, an accurate and autonomous star acquisition method is proposed. Mathematical morphology and variable thresholding are combined for accurate star extraction; motion PSF is estimated in frequency domain and nonlinear filter is adopted for star restoration. Accurate star acquisition can be achieved based on only one star image. Simulations and laboratory experiments are conducted for verification. Several existing methods are also reproduced for comparison. Acquisition results demonstrate that the proposed method is effective and an excellent performance can be achieved autonomously under complex conditions, along with more detected stars and improved acquisition accuracy.

  9. Photometric and polarimetric variability and mass-loss rate of the massive binary Wolf-Rayet star HDE 311884 (WN6 + 05: V)

    International Nuclear Information System (INIS)

    Moffat, A.F.J.; Drissen, L.; Robert, C.; Lamontagne, R.; Coziol, R.

    1990-01-01

    Photometric and polarimetric monitoring of the Wolf-Rayet (W-R) + O-type binary system HDE 311884 = WR 47 over many orbital cycles shows the clear effects of phase-dependent electron scattering of O-star light as the orbiting O companion shines through varying column density of W-R stellar wind material. In contrast to this wind-type eclipse, the stars themselves do not quite eclipse. Both photometry and polarimetry give a consistent estimate of the mass-loss rate of the W-R component: at about 0.00003 solar mass/yr. The orbital inclination, i = 70 deg, along with the previously published velocity orbit, yields high masses: M(WN6) = 48 solar masses and M(O5:V) = 57 solar masses. 33 refs

  10. 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

  11. Dark stars

    DEFF Research Database (Denmark)

    Maselli, Andrea; Pnigouras, Pantelis; Nielsen, Niklas Grønlund

    2017-01-01

    to the formation of compact objects predominantly made of dark matter. Considering both fermionic and bosonic (scalar φ4) equations of state, we construct the equilibrium structure of rotating dark stars, focusing on their bulk properties and comparing them with baryonic neutron stars. We also show that these dark...... objects admit the I-Love-Q universal relations, which link their moments of inertia, tidal deformabilities, and quadrupole moments. Finally, we prove that stars built with a dark matter equation of state are not compact enough to mimic black holes in general relativity, thus making them distinguishable...

  12. Pulsating star research and the Gaia revolution

    Directory of Open Access Journals (Sweden)

    Eyer Laurent

    2017-01-01

    Full Text Available In this article we present an overview of the ESA Gaia mission and of the unprecedented impact that Gaia will have on the field of variable star research. We summarise the contents and impact of the first Gaia data release on the description of variability phenomena, with particular emphasis on pulsating star research. The Tycho-Gaia astrometric solution, although limited to 2.1 million stars, has been used in many studies related to pulsating stars. Furthermore a set of 3,194 Cepheids and RR Lyrae stars with their times series have been released. Finally we present the plans for the ongoing study of variable phenomena with Gaia and highlight some of the possible impacts of the second data release on variable, and specifically, pulsating stars.

  13. Star formation

    International Nuclear Information System (INIS)

    Woodward, P.R.

    1978-01-01

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references

  14. Star formation

    Energy Technology Data Exchange (ETDEWEB)

    Woodward, P.R.

    1978-09-27

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references.

  15. 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)

  16. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star....

  17. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Andersen, Thomas Lykke

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star....

  18. The MACHO Project SMC Variable Star Inventory: I. The Second-overtone Mode of Cepheid Pulsation From First/Second Overtone (1H/2H) Beat Cepheids

    OpenAIRE

    The MACHO Collaboration; Alcock, C.; Allsman, R. A.; Alves, D.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Griest, K.; Lehner, M. J.; Marshall, S. L.; Peterson, B. A.; Quinn, P. J.; Rodgers, A. W.

    1997-01-01

    We report the discovery of 20 1H/2H and 7 F/1H beat Cepheids in the SMC by the MACHO Project. We utilize the 20 1H/2H stars to determine lightcurve shape for the SMC second-overtone (2H) mode of Cepheid pulsation. We predict, similar to the findings of Alcock et al. (1997, ApJ, submitted), that 2H Cepheids will have nearly or purely sinusoidal light variations; that the P-L relation for 2H Cepheids will not be distinguishable from the P-L relation for 1H Cepheids within photometric accuracy; ...

  19. AgapeZ1 a Large Amplification Microlensing Event or an Odd Variable Star Towards the Inner Bulge of M31

    CERN Document Server

    Ansari, R.; Baillon, P.; Bouquet, A.; Coupinot, G.; Coutures, Ch.; Ghesquiere, C.; Giraud-Heraud, Y.; Gondolo, P.; Hecquet, J.; Kaplan, J.; Kim, A.; Du, Y.Le; Melchior, A.L.; Moniez, M.; Picat, J.P.; Soucail, G.; Coutures, Ch.

    1999-01-01

    AgapeZ1 is the brightest and the shortest duration microlensing candidate event found in the Agape data. It occured only 42" from the center of M31. Our photometry shows that the half intensity duration of the event6 is 4.8 days and at maximum brightness we measure a stellar magnitude of R=18.0 with B-R=0.80 mag color. A search on HST archives produced a single resolved star within the projected event position error box. Its magnitude is R=22.

  20. Late Pleistocene-Holocene cataclysmic eruptions at Nevado de Toluca and Jocotitlan volcanoes, central Mexico

    Science.gov (United States)

    Macias, J.L.; Garcia, P.A.; Arce, J.L.; Siebe, C.; Espindola, J.M.; Komorowski, J.C.; Scott, K.

    1997-01-01

    This field guide describes a five day trip to examine deposits of Late Pleistocene-Holocene cataclysmic eruptions at Nevado de Toluca and Jocotitlan volcanoes in central Mexico. We will discuss the stratigraphy, petrology, and sedimentological characteristics of these deposits which provide insights into the eruptive history, type of volcanic activity, and transport and emplacement mechanisms of pyroclastic materials. These parameters will allow us to discuss the kinds of hazards and the risk that they pose to populations around these volcanoes. The area to be visited is tectonically complex thus we will also discuss the location of the volcanoes with respect to the tectonic environment. The first four days of the field trip will be dedicated to Nevado de Toluca Volcano (19 degrees 09'N; 99 degrees 45'W) located at 23 km. southwest of the City of Toluca, and is the fourth highest peak in the country, reaching an elevation of 4,680 meters above sea level (m.a.s.l.). Nevado de Toluca is an andesitic-dacitic stratovolcano, composed of a central vent excavated upon the remains of older craters destroyed by former events. Bloomfield and Valastro, (1974, 1977) concluded that the last cycle of activity occurred nearly equal 11,600 yr. ago. For this reason Nevado de Toluca has been considered an extinct volcano. Our studies, however, indicate that Nevado de Toluca has had at least two episodes of cone destruction by sector collapse as well as several explosive episodes including plinian eruptions and dome-destruction events. These eruptions occurred during the Pleistocene but a very young eruption characterized by surge and ash flows occurred ca. 3,300 yr. BP. This new knowledge of the volcano's eruptive history makes the evaluation of its present state of activity and the geological hazards necessary. This is important because the area is densely populated and large cities such as Toluca and Mexico are located in its proximity.

  1. La mort de Tupac Amaru, l’ultime cataclysme ?

    Directory of Open Access Journals (Sweden)

    Nejma Jalal-Kermele

    2011-06-01

    Full Text Available L’exécution du jeune Inca Tupac Amaru en 1572 fut pour les Indiens du Pérou un véritable cataclysme. Il s’insérait dans un contexte particulier : celui de la vice-royauté du Pérou qui connaissait, depuis de longues années, une série de guerres et de complots. Au cœur de cet espace troublé, se trouvait un royaume néo-inca que la Couronne espérait vaincre par une politique du compromis. Toledo, envoyé pour faire rentrer le Pérou dans un ordre nouveau, avait marqué, dès le début de son gouvernement, son opposition au régime de Vilcabamba dont la seule présence fragilisait la légitimité du pouvoir du roi de Castille aux Indes. C’était donc la question des Justes Titres qui préoccupait Toledo, décidé à lutter activement contre la pensée de Las Casas. La mort d’un messager, envoyé pour négocier avec l’Inca, servit de prétexte à une attaque de Vilcabamba qui permit l’arrestation du jeune Tupac Amaru que le vice-roi décida de condamner à mort, en dépit de sa conversion au catholicisme. L’exécution marqua pour les Indiens la fin d’un monde, la fin d’un espoir et apparut comme l’ultime catastrophe, une répétition de la mort de l’Inca et des Dieux. De nombreux récits rapportent la détresse infinie des Indiens et la désapprobation quasi générale des témoins. Nous voudrions proposer ici une rapide analyse des différentes lectures du cataclysme et tenter de montrer que, pour Toledo, il s’inséra dans une politique claire et assumée. Outre la question idéologique, le vice-roi s’appuya sur des arguments sécuritaires et fit finalement de Tupac Amaru non un prince mais un simple délinquant de droit commun. Cette réécriture de l’Histoire permit d’instaurer une nouvelle définition de la politique espagnole au Pérou mais le cataclysme marqua les esprits et Tupac Amaru, loin d’être oublié, devint un symbole qui traversa les siècles jusqu’à aujourd’hui.La ejecución del joven

  2. Pulsating Star Mystery Solved

    Science.gov (United States)

    2010-11-01

    By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. Up to now astronomers had two incompatible theoretical predictions of Cepheid masses. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations. The new results, from a team led by Grzegorz Pietrzyński (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the 25 November 2010 edition of the journal Nature. Grzegorz Pietrzyński introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct." Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun [1]. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe [2]. Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20-30% less than predictions from the theory of the

  3. 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.

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

    Science.gov (United States)

    Arias, J. P. Sánchez; Córsico, A. H.; Romero, A. D.; Althaus, L. G.

    2017-09-01

    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.

  5. 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.

  6. Hybrid stars

    Indian Academy of Sciences (India)

    physics pp. 753-756. Hybrid stars. AsHOK GOYAL. Department of Physics and Astrophysics, University of Delhi, Delhi 110 007, India. Abstract. Recently there have been important developments in the determination of neutron ... be composed of normal nuclear matter with hyperons and/or condensed mesons. The matter at ...

  7. Star Conquest

    OpenAIRE

    Porrino Serrano, Fernando

    2014-01-01

    Star Conquest es un juego de mesa "print n play" de estrategia por turnos para dos o tres jugadores. Éste proyecto consiste en tomar el juego de mesa original y desarrollar una adaptación en forma de videojuego para distintas plataformas

  8. Hybrid stars

    Indian Academy of Sciences (India)

    Hybrid stars. AsHOK GOYAL. Department of Physics and Astrophysics, University of Delhi, Delhi 110 007, India. Abstract. Recently there have been important developments in the determination of neutron ... number and the electric charge. ... available to the system to rearrange concentration of charges for a given fraction of.

  9. Pulsating stars

    CERN Document Server

    Catelan, M?rcio

    2014-01-01

    The most recent and comprehensive book on pulsating stars which ties the observations to our present understanding of stellar pulsation and evolution theory.  Written by experienced researchers and authors in the field, this book includes the latest observational results and is valuable reading for astronomers, graduate students, nuclear physicists and high energy physicists.

  10. Carbon stars

    International Nuclear Information System (INIS)

    Azzopardi, M.; Lequeux, J.; Rebeirot, E.

    1985-01-01

    Several stars of this type have just been detected in galaxies where they were not suspected and where they reveal a recent activity not really corresponding to current ideas. Data given by these observations allow the astrophysicists to improve the galaxy evolution models, in particular the evolution model of our galaxy [fr

  11. White dwarfs in cataclysmic variables - Low state IUE observations of V794 Aquilae, MR Serpentis, and AN Ursae Majoris

    Science.gov (United States)

    Szkody, Paula; Mateo, Mario; Downes, Ronald

    1988-01-01

    IUE low-dispersion observations of one novalike system (V794 Aql) and two AM Her systems (MR Ser and AN UMa) during low or intermediate-low accretion-rate states are reported. The decreased UV emission during these times was used to place limits on the white dwarf temperatures. When these results are added to the existing data on white dwarf temperatures, it appears that the white dwarfs in systems with normal high accretion rates and only occasional low-accretion-rate states remain hotter than the white dwarfs in systems with low average accretion rates.

  12. 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)

  13. Star Products and Applications

    OpenAIRE

    Iida, Mari; Yoshioka, Akira

    2010-01-01

    Star products parametrized by complex matrices are defined. Especially commutative associative star products are treated, and star exponentials with respect to these star products are considered. Jacobi's theta functions are given as infinite sums of star exponentials. As application, several concrete identities are obtained by properties of the star exponentials.

  14. A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

    International Nuclear Information System (INIS)

    Arneson, R. A.; Gehrz, R. D.; Woodward, C. E.; Shenoy, D.; Helton, L. A.; Evans, A.; Keller, L. D.; Hinkle, K. H.; Jura, M.; Lebzelter, T.; Lisse, C. M.; Rushton, M. T.; Mizrachi, J.

    2017-01-01

    We present a SOFIA FORCAST grism spectroscopic survey to examine the mineralogy of the circumstellar dust in a sample of post-asymptotic giant branch (post-AGB) yellow supergiants that are believed to be the precursors of planetary nebulae. Our mineralogical model of each star indicates the presence of both carbon-rich and oxygen-rich dust species—contrary to simple dredge-up models—with a majority of the dust in the form of amorphous carbon and graphite. The oxygen-rich dust is primarily in the form of amorphous silicates. The spectra do not exhibit any prominent crystalline silicate emission features. For most of the systems, our analysis suggests that the grains are relatively large and have undergone significant processing, supporting the hypothesis that the dust is confined to a Keplerian disk and that we are viewing the heavily processed, central regions of the disk from a nearly face-on orientation. These results help to determine the physical properties of the post-AGB circumstellar environment and to constrain models of post-AGB mass loss and planetary nebula formation.

  15. A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

    Energy Technology Data Exchange (ETDEWEB)

    Arneson, R. A.; Gehrz, R. D.; Woodward, C. E.; Shenoy, D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 106 Pleasant Street S.E., Minneapolis, MN 55455 (United States); Helton, L. A. [USRA-SOFIA Science Center, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Evans, A. [Astrophysics Group, Lennard Jones Laboratory, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Keller, L. D. [Department of Physics and Astronomy, 264 Center for Natural Sciences, Ithaca College, Ithaca, NY 14850 (United States); Hinkle, K. H. [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States); Jura, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Lebzelter, T. [Institute for Astrophysics (IfA), University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria); Lisse, C. M. [Solar System Exploration Branch, Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723 (United States); Rushton, M. T. [Astronomical Institute of the Romanian Academy, Str. Cutitul de Argint 5, Bucharest, 040557 (Romania); Mizrachi, J., E-mail: arneson@astro.umn.edu [Biomedical Engineering Department, Stony Brook University, Stony Brook, NY 11794 (United States)

    2017-07-01

    We present a SOFIA FORCAST grism spectroscopic survey to examine the mineralogy of the circumstellar dust in a sample of post-asymptotic giant branch (post-AGB) yellow supergiants that are believed to be the precursors of planetary nebulae. Our mineralogical model of each star indicates the presence of both carbon-rich and oxygen-rich dust species—contrary to simple dredge-up models—with a majority of the dust in the form of amorphous carbon and graphite. The oxygen-rich dust is primarily in the form of amorphous silicates. The spectra do not exhibit any prominent crystalline silicate emission features. For most of the systems, our analysis suggests that the grains are relatively large and have undergone significant processing, supporting the hypothesis that the dust is confined to a Keplerian disk and that we are viewing the heavily processed, central regions of the disk from a nearly face-on orientation. These results help to determine the physical properties of the post-AGB circumstellar environment and to constrain models of post-AGB mass loss and planetary nebula formation.

  16. Period changes of the long-period cataclysmic binary EX Draconis

    Czech Academy of Sciences Publication Activity Database

    Pilarčík, L.; Wolf, M.; Dubovsky, P.A.; Hornoch, Kamil; Kotková, Lenka

    2012-01-01

    Roč. 539, March (2012), A153/1-A153/5 ISSN 0004-6361 Institutional support: RVO:67985815 Keywords : close binaries * eclipsing * stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  17. A search for new hot subdwarf stars by means of Virtual Observatory tools

    Science.gov (United States)

    Oreiro, R.; Rodríguez-López, C.; Solano, E.; Ulla, A.; Østensen, R.; García-Torres, M.

    2011-06-01

    Context. Recent massive sky surveys in different bandwidths are providing new opportunities to modern astronomy. The Virtual Observatory (VO) provides the adequate framework to handle the huge amount of information available and filter out data according to specific requirements. Aims: Hot subdwarf stars are faint, blue objects, and are the main contributors to the far-UV excess observed in elliptical galaxies. They offer an excellent laboratory to study close and wide binary systems, and to scrutinize their interiors through asteroseismology, since some of them undergo stellar oscillations. However, their origins are still uncertain, and increasing the number of detections is crucial to undertake statistical studies. In this work, we aim at defining a strategy to find new, uncatalogued hot subdwarfs. Methods: Making use of VO tools we thoroughly search stellar catalogues to retrieve multi-colour photometry and astrometric information of a known sample of blue objects, including hot subdwarfs, white dwarfs, cataclysmic variables and main-sequence OB stars. We define a procedure to distinguish among these spectral classes, which is particularly designed to obtain a hot subdwarf sample with a low contamination factor. To check the validity of the method, this procedure is then applied to two test sky regions: to the Kepler FoV and to a test region of 300 deg2 around (α:225, δ:5) deg. Results: As a result of the procedure we obtained 38 hot subdwarf candidates, 23 of which had already a spectral classification. We have acquired spectroscopy for three other targets, and four additional ones have an available SDSS spectrum, which we used to determine their spectral type. A temperature estimate is provided for the candidates based on their spectral energy distribution, considering two-atmospheres fit for objects with clear infrared excess as a signature of the presence of a cool companion. Eventually, out of 30 candidates with spectral classification, 26 objects were

  18. The NuSTAR Hard X-Ray Survey of the Norma Arm Region

    Energy Technology Data Exchange (ETDEWEB)

    Fornasini, Francesca M. [Astronomy Department, University of California, 601 Campbell Hall, Berkeley, CA 94720 (United States); Tomsick, John A.; Chiu, Jeng-Lun; Clavel, Maïca; Krivonos, Roman A.; Boggs, Steven E.; Craig, William W. [Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720 (United States); Hong, JaeSub [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gotthelf, Eric V.; Hailey, Charles J.; Mori, Kaya [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Bauer, Franz; Corral-Santana, Jesús [Instituto de Astrofísica and Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22 (Chile); Rahoui, Farid [European Southern Observatory, K. Schwarzschild-Strasse 2, D-85748 Garching bei München (Germany); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Bodaghee, Arash [Georgia College, 231 W. Hancock Street, Milledgeville, GA 31061 (United States); Alexander, David M. [Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham, DH1 3LE (United Kingdom); Barret, Didier [Université de Toulouse, UPS-OMP, IRAP, Toulouse (France); CNRS, Institut de Recherche en Astrophysique et Planétologie, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France); Christensen, Finn E., E-mail: f.fornasini@berkeley.edu [DTU Space—National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); and others

    2017-04-01

    We present a catalog of hard X-ray sources in a square-degree region surveyed by the Nuclear Spectroscopic Telescope Array ( NuSTAR ) in the direction of the Norma spiral arm. This survey has a total exposure time of 1.7 Ms, and the typical and maximum exposure depths are 50 ks and 1 Ms, respectively. In the area of deepest coverage, sensitivity limits of 5 × 10{sup −14} and 4 × 10{sup −14} erg s{sup −1} cm{sup −2} in the 3–10 and 10–20 keV bands, respectively, are reached. Twenty-eight sources are firmly detected, and 10 are detected with low significance; 8 of the 38 sources are expected to be active galactic nuclei. The three brightest sources were previously identified as a low-mass X-ray binary, high-mass X-ray binary, and pulsar wind nebula. Based on their X-ray properties and multiwavelength counterparts, we identify the likely nature of the other sources as two colliding wind binaries, three pulsar wind nebulae, a black hole binary, and a plurality of cataclysmic variables (CVs). The CV candidates in the Norma region have plasma temperatures of ≈10–20 keV, consistent with the Galactic ridge X-ray emission spectrum but lower than the temperatures of CVs near the Galactic center. This temperature difference may indicate that the Norma region has a lower fraction of intermediate polars relative to other types of CVs compared to the Galactic center. The NuSTAR log N –log S distribution in the 10–20 keV band is consistent with the distribution measured by Chandra at 2–10 keV if the average source spectrum is assumed to be a thermal model with kT  ≈ 15 keV, as observed for the CV candidates.

  19. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter; Brorsen, Michael

    Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004.......Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004....

  20. Strangeon Stars

    Science.gov (United States)

    Lu, Jiguang; Xu, Renxin

    Stable micro-nucleus is 2-flavored (u and d), whereas stable macro-nucleus could be 3-flavored (u, d, and s) if the light flavor symmetry restores there. Nucleons are the constituent of a nucleus, while strangeons are named as the constituent of 3-flavored baryonic matter. Gravity-compressed baryonic object created after core-collapse supernova could be strangeon star if the energy scale (˜0.5 GeV) cannot be high enough for quark deconfinement and if there occurs 3-flavor symmetry restoration. Strangeon stars are explained here, including their formation and manifestation/identification. Much work, coupled with effective micro-model of strangeon matter, is needed to take advantage of the unique opportunities advanced facilities will provide.

  1. On the Binarity of LBV Stars

    NARCIS (Netherlands)

    Martayan, C.; Lobel, A.; Baade, D.; Blomme, R.; Frémat, Y.; LeBouquin, J.B.; Selman, F.; Girard, J.; Mérand, A.; Montagnier, G.; Patru, F.; Mawet, D.; Martins, F.; Rivinius, T.; Štefl, S.; Zorec, J.; Semaan, T.; Mehner, a.; Kervella, P.; Sana, H.; Schödel, R.

    2012-01-01

    We report on the binarity of luminous blue variable stars observed with a set of techniques and instruments. Among them, observations at high angular resolution with the VLT-NACO, the VLTI-AMBER and with spectrographs such as the VLT-XSHOOTER allowed us to find several LBV stars as binaries or

  2. On the RR Lyrae Stars in Globulars. V. The Complete Near-infrared (JHK s ) Census of ω Centauri RR Lyrae Variables

    Science.gov (United States)

    Braga, V. F.; Stetson, P. B.; Bono, G.; Dall’Ora, M.; Ferraro, I.; Fiorentino, G.; Iannicola, G.; Marconi, M.; Marengo, M.; Monson, A. J.; Neeley, J.; Persson, S. E.; Beaton, R. L.; Buonanno, R.; Calamida, A.; Castellani, M.; Di Carlo, E.; Fabrizio, M.; Freedman, W. L.; Inno, L.; Madore, B. F.; Magurno, D.; Marchetti, E.; Marinoni, S.; Marrese, P.; Matsunaga, N.; Minniti, D.; Monelli, M.; Nonino, M.; Piersimoni, A. M.; Pietrinferni, A.; Prada-Moroni, P.; Pulone, L.; Stellingwerf, R.; Tognelli, E.; Walker, A. R.; Valenti, E.; Zoccali, M.

    2018-03-01

    We present a new complete near-infrared (NIR, JHK s ) census of RR Lyrae stars (RRLs) in the globular ω Cen (NGC 5139). We collected 15,472 JHK s images with 4–8 m class telescopes over 15 years (2000–2015) covering a sky area around the cluster center of 60 × 34 arcmin2. These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with 10 to 60 measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 (J), 176 (H) and 174 (K s ) RRLs. These data were supplemented with single-epoch JK s magnitudes from VHS and with single-epoch H magnitudes from 2MASS. Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide JHK s magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed-mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (P > 0.7 days) fundamental RRLs. Using predicted period–luminosity–metallicity relations, we derive a true distance modulus of 13.674 ± 0.008 ± 0.038 mag (statistical error and standard deviation of the median) based on spectroscopic iron abundances, and of 13.698 ± 0.004 ± 0.048 mag based on photometric iron abundances. We also found evidence of possible systematics at the 5%–10% level in the zero-point of the period–luminosity relations based on the five calibrating RRLs whose parallaxes had been determined with the HST. This publication makes use of data gathered with the Magellan/Baade Telescope at Las Campanas Observatory, the Blanco Telescope at Cerro Tololo Inter-American Observatory, NTT at La Silla (ESO Program IDs: 64.N-0038(A), 66.D-0557(A), 68.D-0545(A), 073.D-0313(A), ID 073.D-0313(A) and 59.A-9004(D)), VISTA at Paranal (ESO Program ID: 179.A-2010) and VLT at Paranal (ESO Program ID: ID96406).

  3. A pulsation analysis of K2 observations of the subdwarf B star PG 1142-037 during Campaign 1: A subsynchronously rotating ellipsoidal variable

    DEFF Research Database (Denmark)

    Reed, M. D.; Baran, A. S.; Østensen, R. H.

    2016-01-01

    We report a new subdwarf B pulsator, PG 1142-037, discovered during the first full-length campaign of K2, the two-gyro mission of the Kepler space telescope. 14 periodicities have been detected between 0.9 and 2.5 hr with amplitudes below 0.35 parts-per-thousand. We have been able to associate al...... result is the detection of an ellipsoidal, tidally distorted variable with no indication of rotationally induced pulsation multiplets. This indicates that the rotation period is longer than 45 d, even though the binary period is near 13 h....

  4. The Chemical Compositions of the SRd Variable Stars. III. KK Aquilae, AG Aurigae, Z Aurigae, W Leo Minoris, and WW Tauri

    OpenAIRE

    Giridhar, S.; Lambert, D. L.; Gonzalez, G.

    2000-01-01

    Chemical compositions are derived from high-resolution spectra for five field SRd variables. These supergiants not previously analysed are shown to be metal-poor: KK Aql with [Fe/H] = -1.2, AG Aur with [Fe/H] = -1.8, Z Aur with [Fe/H] = -1.4, W LMi with [Fe/H] = -1.1, and WW Tau with [Fe/H] = -1.1. Their compositions are, except for two anomalies, identical to within the measurement errors with the compositions of subdwarfs, subgiants, and less evolved giants of the same [Fe/H]. One anomaly i...

  5. Toward a Better Understanding of the Distance Scale from RR Lyrae Variable Stars: A Case Study for the Inner Halo Globular Cluster NGC 6723

    Science.gov (United States)

    Lee, Jae-Woo; López-Morales, Mercedes; Hong, Kyeongsoo; Kang, Young-Woon; Pohl, Brian L.; Walker, Alistair

    2014-01-01

    We present BV photometry for 54 variables in the metal-rich inner halo globular cluster NGC 6723. With the discovery of new RR Lyrae variables (RRLs), we obtain langP abrang = 0.541 ± 0.066 and langP crang = 0.292 ± 0.030 day, n(c)/n(ab+c) = 0.167, and langV(RR)rangint = 15.459 ± 0.055. We carry out the Fourier decomposition analysis and obtain [Fe/H]ZW = -1.23 ± 0.11 and E(B - V) = 0.063 ± 0.015 for NGC 6723. By calibrating the zero point from the recent absolute trigonometric parallax measurements for RR Lyr, we derive the revised MV (RR)-[Fe/H] relation, providing MV (RR) = 0.52 at [Fe/H] = -1.50 and (m - M)0 = 18.54 for the Large Magellanic Cloud, in excellent agreement with others. We obtain (m - M)0 = 14.65 ± 0.05, equivalent to a distance from the Sun of 8.47 ± 0.17 kpc, for NGC 6723 from various distance measurement methods using RRLs. We find that RRLs in NGC 6723 do not have magnitude dependency on the radial distance because there is not a severe degree of apparent crowdedness. Finally, we show that a relation exists between the degree of photometric contamination and the apparent crowdedness of the central region of globular cluster systems, |\\bar{\\mu } - \\mu _r| \\propto log \\rho _c d^2. The use of this relation can play a significant role in mitigating the discrepancy in establishing a cosmic distance scale using RRLs in resolved stellar populations in near-field cosmology. Partially based on observations made with telescopes operated by the SMARTS consortium.

  6. Separable metrics and radiating stars

    Indian Academy of Sciences (India)

    We study the junction condition relating the pressure to heat flux at the boundary of an accelerating and expanding spherically symmetric radiating star. We transform the junction condition to an ordinary differential equation by making a separability assumption on the metric functions in the space–time variables.

  7. Photometry of variable AFGL sources

    International Nuclear Information System (INIS)

    Jones, T.J.; Bryja, C.O.; Gehrz, R.D.; Harrison, T.E.; Johnson, J.J.

    1990-01-01

    Results of infrared photometric observations of 63 AFGL sources over the past 9 years are presented. Using these data together with previous measurements of these stars, pulsation periods and mean photometric characteristics are determined. These stars are found to lie midway between optically identified Mira variables and the radio-luminous OH/IR stars in their period distribution and photometric properties. For the sample as a whole, there is no evidence for sudden or transient behavior such as a switch in pulsation mode. Rather, these stars suggest rapid, but continuous, evolution from shorter period Miras with weak mass loss to longer periods and larger mass-loss rates. The carbon-rich stars in the sample have the same period distribution as the oxygen-rich stars. None of the carbon stars have periods as long as those of the very long period radio-luminous OH/IR stars. 61 refs

  8. 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.

  9. The R band light curves of eclipses of U Gem in outburst

    Czech Academy of Sciences Publication Activity Database

    Šimon, Vojtěch

    č. 5453 (2003), s. 1-4 ISSN 0374-0676 Institutional research plan: CEZ:AV0Z1003909 Keywords : cataclysmic variables * general binaries stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  10. Rapid variability of blazar 3C 279 during flaring states in 2013-2014 with joint FERMI-LAT, NuSTAR, swift, and ground-based multi-wavelength observations

    DEFF Research Database (Denmark)

    Hayashida, M.; Nalewajko, K.; Madejski, G. M.

    2015-01-01

    reaching the highest flux level measured in this object since the beginning of the Fermi mission, with F (E> 100 MeV) of 10-5 photons cm-2 s-1, and with a flux-doubling time scale as short as 2 hr. The y-ray spectrum during one of the flares was very hard, with an index of Γγ = 1.7 ± 0.1, which is rarely...... seen in flat-spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter Lγ/Lsyn > 300. Two 1 day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5-70 keV X-ray......) extremely low jet magnetization with LB/Lj 10-4. ≲ - We also find that single-zone models that match the observed γ-ray and optical spectra cannot satisfactorily explain the production of X-ray emission....

  11. 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.

  12. Effect of process variables on the osmotic dehydration of star-fruit slices Efeito das variáveis de processo na desidratação osmótica de fatias de carambola

    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.O objetivo deste trabalho foi estudar o efeito do branqueamento e a influência da temperatura, concentração de sacarose e da relação fruta:solução inicial na desidratação osmótica de fatias de carambola. Para o branqueamento, diferentes concentrações de ácido cítrico e ascórbico foram estudadas. As amostras imersas em 0,75% de ácido cítrico apresentaram pouca variação de cor em relação à carambola fresca. A desidratação osmótica foi conduzida em uma incubadora com agitação orbital, com temperatura controlada e agitação constante de 120 rpm. A influência das variáveis de processo foi avaliada através de ensaios definidos

  13. 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.

  14. 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.)

  15. Photometric Variability of Four Coronally Active Stars

    Indian Academy of Sciences (India)

    Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately.

  16. 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

  17. 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)

  18. Giant CP stars

    International Nuclear Information System (INIS)

    Loden, L.O.; Sundman, A.

    1989-01-01

    This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary 'non giant' CP stars. There is no clear confirmation of a higher luminosity for 'CP giants', than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members. (author). 50 refs., 5 tabs., 3 figs

  19. Temperature, salinity and other variables collected from discrete sample and profile observations using CTD, bottle and other instruments from USCGC POLAR STAR in the Arctic Ocean from 2002-08-19 to 2002-09-23 (NODC Accession 0115588)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NCEI Accession 0115588 includes discrete sample and profile data collected from USCGC POLAR STAR in the Arctic Ocean from 2002-08-19 to 2002-09-23. These data...

  20. Spectral Properties and Variability of BIS objects

    Science.gov (United States)

    Gaudenzi, S.; Nesci, R.; Rossi, C.; Sclavi, S.; Gigoyan, K. S.; Mickaelian, A. M.

    2017-10-01

    Through the analysis and interpretation of newly obtained and of literature data we have clarified the nature of poorly investigated IRAS point sources classified as late type stars, belonging to the Byurakan IRAS Stars catalog. From medium resolution spectroscopy of 95 stars we have strongly revised 47 spectral types and newly classified 31 sources. Nine stars are of G or K types, four are N carbon stars in the Asymptotic Giant Branch, the others being M-type stars. From literature and new photometric observations we have studied their variability behaviour. For the regular variables we determined distances, absolute magnitudes and mass loss rates. For the other stars we estimated the distances, ranging between 1.3 and 10 kpc with a median of 2.8 kpc from the galactic plane, indicating that BIS stars mostly belong to the halo population.

  1. 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.

  2. RADIAL VELOCITY MONITORING OF KEPLER HEARTBEAT STARS

    International Nuclear Information System (INIS)

    Shporer, Avi; Fuller, Jim; Isaacson, Howard; Hambleton, Kelly; Prša, Andrej; Thompson, Susan E.; Kurtz, Donald W.; Howard, Andrew W.; O’Leary, Ryan M.

    2016-01-01

    Heartbeat stars (HB stars) are a class of eccentric binary stars with close periastron passages. The characteristic photometric HB signal evident in their light curves is produced by a combination of tidal distortion, heating, and Doppler boosting near orbital periastron. Many HB stars continue to oscillate after periastron and along the entire orbit, indicative of the tidal excitation of oscillation modes within one or both stars. These systems are among the most eccentric binaries known, and they constitute astrophysical laboratories for the study of tidal effects. We have undertaken a radial velocity (RV) monitoring campaign of Kepler HB stars in order to measure their orbits. We present our first results here, including a sample of 22 Kepler HB systems, where for 19 of them we obtained the Keplerian orbit and for 3 other systems we did not detect a statistically significant RV variability. Results presented here are based on 218 spectra obtained with the Keck/HIRES spectrograph during the 2015 Kepler observing season, and they have allowed us to obtain the largest sample of HB stars with orbits measured using a single instrument, which roughly doubles the number of HB stars with an RV measured orbit. The 19 systems measured here have orbital periods from 7 to 90 days and eccentricities from 0.2 to 0.9. We show that HB stars draw the upper envelope of the eccentricity–period distribution. Therefore, HB stars likely represent a population of stars currently undergoing high eccentricity migration via tidal orbital circularization, and they will allow for new tests of high eccentricity migration theories.

  3. Energy production in stars

    International Nuclear Information System (INIS)

    Bethe, Hans.

    1977-01-01

    Energy in stars is released partly by gravitation, partly by nuclear reactions. For ordinary stars like our sun, nuclear reactions predominate. However, at the end of the life of a star very large amounts of energy are released by gravitational collapse; this can amount to as much as 10 times the total energy released nuclear reactions. The rotational energy of pulsars is a small remnant of the energy of gravitation. The end stage of small stars is generally a white dwarf, of heavy stars a neutron star of possibly a black hole

  4. Rates of star formation

    International Nuclear Information System (INIS)

    Larson, R.B.

    1977-01-01

    It is illustrated that a theoretical understanding of the formation and evolution of galaxies depends on an understanding of star formation, and especially of the factors influencing the rate of star formation. Some of the theoretical problems of star formation in galaxies, some approaches that have been considered in models of galaxy evolution, and some possible observational tests that may help to clarify which processes or models are most relevant are reviewed. The material is presented under the following headings: power-law models for star formation, star formation processes (conditions required, ways of achieving these conditions), observational indications and tests, and measures of star formation rates in galaxies. 49 references

  5. UXOR Hunting among Algol Variables

    Science.gov (United States)

    Poxon, M.

    2015-06-01

    The class of variable typified by UX Orionis (UXORs or UXors) are young stars characterised by aperiodic or semiperiodic fades from maximum. This has led to several of the class being formerly catalogued as Algol-type eclipsing binaries (EAs), which can show superficially similar light variations. With this in view, I propose a campaign to search for more UX Ori type stars.

  6. The Massive Star Population in M101

    Science.gov (United States)

    Grammer, Skyler; Humphreys, R. M.

    2013-06-01

    Evolved massive stars including luminous blue variables and hypergiants are the likely progenitor class of giant eruptions or supernova impostors (SN impostors). Motivated by the small number of progenitors positively associated with SN impostors, we present a survey of the massive star population in M101. Regions of massive star formation, ranging from 0.05 kpc2 to 50 kpc2, were identified using GALEX FUV and NUV imaging across the face of M101. The resolved stellar populations within each region were extracted from sixteen archival multicolor HST ACS WFC observations and color-magnitude-diagrams (CMD) were created. We have identified red supergiant (RSG) and blue supergiant (BSG) candidates using color and luminosity criteria. The RSG and BSG candidates identified represents the population of stars in M101 likely to be the SN impostor progenitor class. Furthermore we have determined the star formation histories (SFH) for the massive star populations within each region using two methods: CMD modeling, and spectral-energy-distribution fitting. We find that there has been a continuous buildup of massive stars over the last 100 Myr with a sharp increase in star formation rate within the last 20 Myr. Evidence for a decrease in mean stellar ages for regions with increasing radii has also been observed and is consistent with previously observed color gradients in optical and UV.

  7. Characterizing the Habitable Zone Planets of Kepler Stars

    Science.gov (United States)

    Fischer, Debra

    than 100 days or they use extrapolation to estimate planet occurrence rates beyond 100 days. The new detections of transit candidates at wider separations and the incompleteness analysis will be used to carry out an analysis of the architecture of exoplanetary systems from 1 5 AU. We are synthesizing a statistical description with information from short-period Kepler transits, the longer period Kepler transit candidates from this proposal, a completeness analysis of radial velocity data, and statistical information from microlensing. While our architecture analysis will only sketch out the bare bones of planetary systems (massive or large planets), this is still a novel analysis that may point to the location of rocky planets if packed planetary systems prevail. Finally, we will expand our guest scientist program for serendipitous discoveries. We have already partnered with scientists who are searching for cataclysmic variables, heartbeat stars, and exomoons. Our undergrad students have already carried out summer research as guest scientists to characterize inflated jupiters, search for Trojan planets, and to search for microlensing events.

  8. Regular Generalized Star Star closed sets in Bitopological Spaces

    OpenAIRE

    K. Kannan; D. Narasimhan; K. Chandrasekhara Rao; R. Ravikumar

    2011-01-01

    The aim of this paper is to introduce the concepts of τ1τ2-regular generalized star star closed sets , τ1τ2-regular generalized star star open sets and study their basic properties in bitopological spaces.

  9. Pulsation of Ap-Stars

    Science.gov (United States)

    Weiss, W. W.; Schneider, H.

    1983-09-01

    It has been known for many centuries that one can determine by simple means if a barrel of wine is full, half empty, or- horribile dictu - empty. One knocks against the wall and listens to the echo. Another example of the same technique, but less interesting for the connaisseur en vin is given by seismology. Seismographs distributed all over the globe register earthquakes and since they are differently located with respect to an earthquake centre the registrations look different. From a comparison of such registrations geologists have extracted most of our knowledge about the structure and composition of the terrestrial interior. Corresponding experiments were also planned and successfully executed on the Moon and on Mars. Stellar astronomers, however, are not in the lucky position of their colleagues who work in our solar system with the help of satellites. They are limited to stars which pulsate voluntarily. We will not discuss here the question why some groups of stars pulsate and others do not. We shall only mention that pulsating stars have at least one layer in their interior which does not absorb pulsational energy, as is the case for the rest of the star, but produces energy of variable amount and in phase with PUlsation. This mechanism keeps the star pulsating as long as this (these) layer(s) exists. Oue to stellar evolution, diffusion, magnetic fields, to name only some possible mechanisms, these layers can disappear or undergo substantial changes so that the energy losses due to pulsation cannot be compensated anymore. Oamping will result and finally the star will become stable against pulsation.

  10. 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

  11. 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.

  12. Quark core stars, quark stars and strange stars

    International Nuclear Information System (INIS)

    Grassi, F.

    1988-01-01

    A recent one flavor quark matter equation of state is generalized to several flavors. It is shown that quarks undergo a first order phase transition. In addition, this equation of state depends on just one parameter in the two flavor case, two parameters in the three flavor case, and these parameters are constrained by phenomenology. This equation of state is then applied to the hadron-quark transition in neutron stars and the determination of quark star stability, the investigation of strange matter stability and possible strange star existence. 43 refs., 6 figs

  13. ENERGY STAR Certified Televisions

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Televisions that are effective as of October 30,...

  14. mSTAR

    Data.gov (United States)

    National Aeronautics and Space Administration — Mini-STAR (mSTAR) is a small satellite mission concept to test the hypothesis that the velocity of light is independent of the velocity and orientation of the...

  15. ENERGY STAR Certified Boilers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Boilers that are effective as of October 1,...

  16. Observations of central stars

    International Nuclear Information System (INIS)

    Lutz, J.H.

    1978-01-01

    Difficulties occurring in the observation of central stars of planetary nebulae are reviewed with emphasis on spectral classifications and population types, and temperature determination. Binary and peculiar central stars are discussed. (U.M.G.)

  17. ENERGY STAR Certified Computers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 6.1 ENERGY STAR Program Requirements for Computers that are effective as of June 2, 2014....

  18. ENERGY STAR Certified Furnaces

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.1 ENERGY STAR Program Requirements for Furnaces that are effective as of February 1,...

  19. ENERGY STAR Certified Telephones

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Telephony (cordless telephones and VoIP...

  20. ENERGY STAR Certified Dehumidifiers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Dehumidifiers that are effective as of October...

  1. Autonomous Star Tracker Algorithms

    DEFF Research Database (Denmark)

    Betto, Maurizio; Jørgensen, John Leif; Kilsgaard, Søren

    1998-01-01

    Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances.......Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances....

  2. America's Star Libraries

    Science.gov (United States)

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  3. 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

  4. ENIGMATIC RECURRENT PULSATIONAL VARIABILITY OF THE ACCRETING WHITE DWARF EQ LYN (SDSS J074531.92+453829.6)

    Energy Technology Data Exchange (ETDEWEB)

    Mukadam, Anjum S.; Szkody, Paula [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Townsley, D. M.; Brockett, T. [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487 (United States); Gaensicke, B. T.; Parsons, S. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Southworth, J. [Astrophysics Group, Keele University, Staffordshire ST5 5BG (United Kingdom); Hermes, J. J.; Montgomery, M. H.; Winget, D. E.; Harrold, S. [Department of Astronomy, University of Texas at Austin, Austin, TX 78759 (United States); Tovmassian, G.; Zharikov, S. [Observatorio Astronomico Nacional SPM, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ensenada, BC (Mexico); Drake, A. J. [Department of Astronomy and the Center for Advanced Computing Research, California Institute of Technology, Pasadena, CA 91225 (United States); Henden, A. [American Association of Variable Star Observers, 25 Birch Street, Cambridge, MA 02138 (United States); Rodriguez-Gil, P. [Departamento de Astrofisica, Universidad de La Laguna, La Laguna, E-38204 Santa Cruz de Tenerife (Spain); Sion, E. M. [Department of Astronomy and Astrophysics, Villanova University, Villanova, PA 19085 (United States); Zola, S.; Szymanski, T. [Astronomical Observatory, Jagiellonian University, ul. Orla 171, PL-30-244 Krakow (Poland); Pavlenko, E. [Crimean Astrophysical Observatory, Crimea 98409 (Ukraine); and others

    2013-09-15

    Photometric observations of the cataclysmic variable EQ Lyn (SDSS J074531.92+453829.6), acquired from 2005 October to 2006 January, revealed high-amplitude variability in the range 1166-1290 s. This accreting white dwarf underwent an outburst in 2006 October, during which its brightness increased by at least five magnitudes, and it started exhibiting superhumps in its light curve. Upon cooling to quiescence, the superhumps disappeared and it displayed the same periods in 2010 February as prior to the outburst within the uncertainties of a couple of seconds. This behavior suggests that the observed variability is likely due to nonradial pulsations in the white dwarf star, whose core structure has not been significantly affected by the outburst. The enigmatic observations begin with an absence of pulsational variability during a multi-site campaign conducted in 2011 January-February without any evidence of a new outburst; the light curve is instead dominated by superhumps with periods in the range of 83-87 minutes. Ultraviolet Hubble Space Telescope time-series spectroscopy acquired in 2011 March reveals an effective temperature of 15,400 K, placing EQ Lyn within the broad instability strip of 10,500-16,000 K for accreting pulsators. The ultraviolet light curve with 90% flux from the white dwarf shows no evidence of any pulsations. Optical photometry acquired during 2011 and Spring 2012 continues to reflect the presence of superhumps and an absence of pulsations. Subsequent observations acquired in 2012 December and 2013 January finally indicate the disappearance of superhumps and the return of pulsational variability with similar periods as previous data. However, our most recent data from 2013 March to May reveal superhumps yet again with no sign of pulsations. We speculate that this enigmatic post-outburst behavior of the frequent disappearance of pulsational variability in EQ Lyn is caused either by heating the white dwarf beyond the instability strip due to an

  5. 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)

  6. Rotating Stars in Relativity

    Directory of Open Access Journals (Sweden)

    Stergioulas Nikolaos

    2003-01-01

    Full Text Available Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on the equilibrium properties and on the nonaxisymmetric instabilities in f-modes and r-modes have been updated and several new sections have been added on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity.

  7. Magnetism of hot stars

    Science.gov (United States)

    Wade, G. A.; Neiner, C.

    2018-01-01

    Strong, stable, and organised magnetic fields are present at the surfaces of a small fraction of OBA stars. These "fossil fields" exhibit uniform characteristics in stars over a tremendous range of stellar mass, age, temperature, and rotation rate. In hot O- and B-type stars, these magnetic fields couple efficiently to the stellar radiatively driven winds, strongly influencing stellar mass loss and rotation. In this article we review the characteristics of the known magnetic hot stars, discuss recent discoveries and insights, and describe recent theoretical progress toward understanding basic field properties and the influence of magnetic fields on hot star evolution.

  8. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2015-01-01

    Most elements are synthesized, or ""cooked"", by thermonuclear reactions in stars. The newly formed elements are released into the interstellar medium during a star's lifetime, and are subsequently incorporated into a new generation of stars, into the planets that form around the stars, and into the life forms that originate on the planets. Moreover, the energy we depend on for life originates from nuclear reactions that occur at the center of the Sun. Synthesis of the elements and nuclear energy production in stars are the topics of nuclear astrophysics, which is the subject of this book

  9. A decade of UV astronomy with the IUE satellite. Volume 1

    International Nuclear Information System (INIS)

    Rolfe, E.J.

    1988-06-01

    These proceedings present recent I.U.E. results and also reviews of some selected topics studied with this satellite: solar system science, supernovae and their remnants, X-ray and cataclysmic binary systems, binary stars circumstellar matter and mass transfer, white dwarf stars, stellar activity, stellar atmospheres and variable stars

  10. THE FIRST STARS

    Directory of Open Access Journals (Sweden)

    Daniel J. Whalen

    2013-12-01

    Full Text Available Pop III stars are the key to the character of primeval galaxies, the first heavy elements, the onset of cosmological reionization, and the seeds of supermassive black holes. Unfortunately, in spite of their increasing sophistication, numerical models of Pop III star formation cannot yet predict the masses of the first stars. Because they also lie at the edge of the observable universe, individual Pop III stars will remain beyond the reach of observatories for decades to come, and so their properties are unknown. However, it will soon be possible to constrain their masses by direct detection of their supernovae, and by reconciling their nucleosynthetic yields to the chemical abundances measured in ancient metal-poor stars in the Galactic halo, some of which may bear the ashes of the first stars. Here, I review the state of the art in numerical simulations of primordial stars and attempts to directly and indirectly constrain their properties.

  11. Ponderable soliton stars

    Science.gov (United States)

    Chiu, Hong-Yee

    1990-01-01

    The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

  12. Massive Star Burps, Then Explodes

    Science.gov (United States)

    2007-04-01

    event was a complete surprise," added Alex Filippenko, leader of the UC Berkeley/Keck supernova group and a member of NASA'S Swift team. "It opens up a fascinating new window on how some kinds of stars die." All the observations suggest that the supernova's blast wave took only a few weeks to reach the shell of material ejected two years earlier, which did not have time to drift very far from the star. As the wave smashed into the ejecta, it heated the gas to millions of degrees, hot enough to emit copious X-rays. The Swift satellite saw the supernova continue to brighten in X-rays for 100 days, something that has never been seen before in a supernova. All supernovae previously observed in X-rays have started off bright and then quickly faded to invisibility. "You don't need a lot of mass in the ejecta to produce a lot of X-rays," notes Immler. Swift's ability to monitor the supernova's X-ray rise and decline over six months was crucial to his team's mass determination. But he adds that Chandra's sharp resolution enabled his group to resolve the supernova from a bright X-ray source that appears in the field of view of Swift's X-ray Telescope. "We could not have made this measurement without Chandra," says Immler, who will submit his team's paper next week to the Astrophysical Journal. "The synergy between Swift's fast response and its ability to observe a supernova every day for a long period, and Chandra's high spatial resolution, is leading to a lot of interesting results." Foley and his colleagues, whose paper appears in the March 10 Astrophysical Journal Letters, propose that the star recently transitioned from a Luminous Blue Variable (LBV) star to a Wolf-Rayet star. An LBV is a massive star in a brief but unstable phase of stellar evolution. Similar to the 2004 eruption, LBVs are prone to blow off large amounts of mass in outbursts so extreme that they are frequently mistaken for supernovae, events dubbed "supernova impostors." Wolf-Rayet stars are hot, highly

  13. International Living With a Star

    Science.gov (United States)

    Brekke, Pål

    2005-08-01

    The response of our space environment to the constantly changing Sun is known as "Space Weather". Sudden ejections of plasma and magnetic field structures from the Sun's atmosphere called coronal mass ejections (CMEs) together with sudden bursts of radiation termed solar flares all cause space weather effects at the Earth. The International Living With a Star (ILWS) programme is a space weather focused and applications driven research programme. Its goal is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun-Earth system that directly affects life and society. Recent large solar storms caused damages to power systems and satellites and disturbed important navigation and communication systems. Furthermore, accurate monitoring of the energy output from the Sun is important for understanding how the Sun contributes to the observed warming of our planet. The Sun is a variable star we better learn how to live with.

  14. 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.

  15. Environments of T Tauri stars

    International Nuclear Information System (INIS)

    Chevalier, R.A.

    1983-01-01

    The environments of T Tauri stars are probably determined by the interaction of a stellar wind with matter which is falling toward a newly formed star. As shown by Ulrich, the steady infall of cool gas with angular momentum toward the star leads to a density distribution with rhoproportionalr/sup -1/2/ inside a radius r/sub d/ and rhoproportionalr/sup -3/2/ outside r/sub d/. The radius r/sub d/ is determined by the angular momentum of the infalling gas. The expansion of the wind into this medium depends on the parameter α = M/sub w/v/sub w//M/sub in/v/sub in/(r/sub d/), where v/sub in/(r/sub d/) is the free-fall velocity at r/sub d/, M/sub in/ is the mass accretion rate, v/sub w/ is the wind velocity, and M/sub w/ is the mass loss rate. For α 14 cm, v/sub w/ = 150 km s -1 , M/sub in/ = 10 -7 M/sub sun/ yr -1 , and M/sub w/ = 3 x 10 -8 M/sub sun/ yr -1 . The inflow is clumpy. The shocked wind gives the radio emission and nebular emission from T Tauri, and dust within the clumps gives the infrared emission. T Tauri is in a transitory phase in which most of the wind has only recently propagated beyond r/sub d/. The model naturally predicts variable obscuration of T Tauri stars because the infalling clumps move on nonradial trajectories. The infrared emission can vary either because of structural changes in the circumstellar gas or because of variations in the stellar luminosity. Infrared variability should be small at short time scales because of light-travel time effects

  16. Star-Branched Polymers (Star Polymers)

    KAUST Repository

    Hirao, Akira

    2015-09-01

    The synthesis of well-defined regular and asymmetric mixed arm (hereinafter miktoarm) star-branched polymers by the living anionic polymerization is reviewed in this chapter. In particular, much attention is being devoted to the synthetic development of miktoarm star polymers since 2000. At the present time, the almost all types of multiarmed and multicomponent miktoarm star polymers have become feasible by using recently developed iterative strategy. For example, the following well-defined stars have been successfully synthesized: 3-arm ABC, 4-arm ABCD, 5-arm ABCDE, 6-arm ABCDEF, 7-arm ABCDEFG, 6-arm ABC, 9-arm ABC, 12-arm ABC, 13-arm ABCD, 9-arm AB, 17-arm AB, 33-arm AB, 7-arm ABC, 15-arm ABCD, and 31-arm ABCDE miktoarm star polymers, most of which are quite new and difficult to synthesize by the end of the 1990s. Several new specialty functional star polymers composed of vinyl polymer segments and rigid rodlike poly(acetylene) arms, helical polypeptide, or helical poly(hexyl isocyanate) arms are introduced.

  17. Dark stars: a review.

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  18. Cataclysmic Rock Avalanche from El Capitan, Yosemite Valley, circa 3.6 ka

    Science.gov (United States)

    Stock, G. M.

    2008-12-01

    variability within boulders from this deposit appears to preclude the use of this technique in this setting. Ongoing detailed geologic mapping of the southeast face may help to resolve the source of the rock avalanche.

  19. VARIABLES IN GLOBULAR CLUSTER NGC 5024

    Energy Technology Data Exchange (ETDEWEB)

    Safonova, M.; Stalin, C. S., E-mail: rita@iiap.res.in, E-mail: stalin@iiap.res.in [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India)

    2011-12-15

    We present the results of a commissioning campaign to observe Galactic globular clusters for the search of microlensing events. The central 10' Multiplication-Sign 10' region of the globular cluster NGC 5024 was monitored using the 2 m Himalayan Chandra Telescope in R-band for a period of about 8 hr on 2010 March 24. Light curves were obtained for nearly 10,000 stars using a modified Differential Image Analysis technique. We identified all known variables within our field of view and revised the periods and status of some previously reported short-period variables. We report about 70 new variable sources and present their equatorial coordinates, periods, light curves, and possible types. Out of these, 15 are SX Phe stars, 10 are W UMa-type stars, and 14 are probable RR Lyrae stars. Nine of the newly discovered SX Phe stars and one eclipsing binary belong to the blue straggler star population.

  20. The search for magnetic fields in mercury-manganese stars

    NARCIS (Netherlands)

    Makaganiuk, V.; Kochukhov, O.; Piskunov, N.; Jeffers, S.V.; Johns-Krull, C. M.; Keller, C.U.; Rodenhuis, M.; Snik, F.; Stempels, H. C.; Valenti, J. A.

    2010-01-01

    A subclass of the upper main-sequence chemically peculiar stars, mercury-manganese (HgMn) stars were traditionally considered to be non-magnetic, showing no evidence of variability in their spectral line profiles. However, discoveries of chemical inhomogeneities on their surfaces imply that this

  1. Spectral Behavior of the "Stable Shell" Star HD 179343

    Czech Academy of Sciences Publication Activity Database

    Iliev, L.; Kubát, Jiří

    2010-01-01

    Roč. 20, Suppl. (2010), s. 33-37 ISSN 1220-5168 Institutional research plan: CEZ:AV0Z10030501 Keywords : variable star s * Be/shell star s * spectral observations Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  2. Seeing Stars in Serpens

    Science.gov (United States)

    2006-01-01

    Infant stars are glowing gloriously in this infrared image of the Serpens star-forming region, captured by NASA's Spitzer Space Telescope. The reddish-pink dots are baby stars deeply embedded in the cosmic cloud of gas and dust that collapsed to create it. A dusty disk of cosmic debris, or 'protoplanetary disk,' that may eventually form planets, surrounds the infant stars. Wisps of green throughout the image indicate the presence of carbon rich molecules called polycyclic aromatic hydrocarbons. On Earth, these molecules can be found on charred barbecue grills and in automobile exhaust. Blue specks sprinkled throughout the image are background stars in our Milky Way galaxy. The Serpens star-forming region is located approximately 848 light-years away in the Serpens constellation. The image is a three-channel, false-color composite, where emission at 4.5 microns is blue, emission at 8.0 microns is green, and 24 micron emission is red.

  3. Nagyszombat and the stars

    Science.gov (United States)

    Zsoldos, E.

    Péter Pázmány, founder of the University of Nagyszombat, considered stars in terms inherited from medieval times. The theses, connected to the university graduation, soon left this definition, and imagined stars as made from sublunar elements. The 1753 decree of the Empress Maria Theresia ordered university professors to publish textbooks. These textbooks, together with the theses showed a definite improvement, defining stars according to contemporary knowledge.

  4. Evolution of massive stars

    International Nuclear Information System (INIS)

    Loore, C. de

    1984-01-01

    The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

  5. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jian-Ying; Ibragimov, Rashid

    2013-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting...... tree is isomorphic to T? We prove that in the general setting, CST is NP-complete, which implies that the tree edit distance considered here is also NP-hard, even when both input trees having diameters bounded by 10. We also show that, when the number of distinct stars is bounded by a constant k, CTS...

  6. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jiong; Ibragimov, Rashid

    2015-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting...... tree is isomorphic to T? We prove that in the general setting, CST is NP-complete, which implies that the tree edit distance considered here is also NP-hard, even when both input trees having diameters bounded by 10. We also show that, when the number of distinct stars is bounded by a constant k, CTS...

  7. Massive soliton stars

    Science.gov (United States)

    Chiu, Hong-Yee

    1990-01-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  8. Interacting binary stars

    CERN Document Server

    Sahade, Jorge; Ter Haar, D

    1978-01-01

    Interacting Binary Stars deals with the development, ideas, and problems in the study of interacting binary stars. The book consolidates the information that is scattered over many publications and papers and gives an account of important discoveries with relevant historical background. Chapters are devoted to the presentation and discussion of the different facets of the field, such as historical account of the development in the field of study of binary stars; the Roche equipotential surfaces; methods and techniques in space astronomy; and enumeration of binary star systems that are studied

  9. ENERGY STAR Unit Reports

    Data.gov (United States)

    Department of Housing and Urban Development — These quarterly Federal Fiscal Year performance reports track the ENERGY STAR qualified HOME units that Participating Jurisdictions record in HUD's Integrated...

  10. Horizontal Branch stars as AmFm/HgMn stars

    OpenAIRE

    Michaud, G.; Richer, J.

    2008-01-01

    Recent observations and models for horizontal branch stars are briefly described and compared to models for AmFm stars. The limitations of those models are emphasized by a comparison to observations and models for HgMn stars.

  11. Living with the stars how the human body is connected to the life cycles of the Earth, the planets, and the stars

    CERN Document Server

    Schrijver, Karel

    2015-01-01

    Living with the Stars tells the fascinating story of what truly makes the human body. The body that is with us all our lives is always changing. We are quite literally not who we were years, weeks, or even days ago: our cells die and are replaced by new ones at an astonishing pace. The entire body continually rebuilds itself, time and again, using the food and water that flow through us as fuel and as construction material. What persists over time is not fixed but merely a pattern in flux. We rebuild using elements captured from our surroundings, and are thereby connected to animals and plants around us, and to the bacteria within us that help digest them, and to geological processes such as continental drift and volcanism here on Earth. We are also intimately linked to the Sun's nuclear furnace and to the solar wind, to collisions with asteroids and to the cycles of the birth of stars and their deaths in cataclysmic supernovae, and ultimately to the beginning of the universe. Our bodies are made of the burn...

  12. How animals follow the stars.

    Science.gov (United States)

    Foster, James J; Smolka, Jochen; Nilsson, Dan-Eric; Dacke, Marie

    2018-01-31

    Throughout history, the stars have provided humans with ever more information about our world, enabling increasingly accurate systems of navigation in addition to fuelling some of the greatest scientific controversies. What information animals have evolved to extract from a starry sky and how they do so, is a topic of study that combines the practical and theoretical challenges faced by both astronomers and field biologists. While a number of animal species have been demonstrated to use the stars as a source of directional information, the strategies that these animals use to convert this complex and variable pattern of dim-light points into a reliable 'stellar orientation' cue have been more difficult to ascertain. In this review, we assess the stars as a visual stimulus that conveys directional information, and compare the bodies of evidence available for the different stellar orientation strategies proposed to date. In this context, we also introduce new technologies that may aid in the study of stellar orientation, and suggest how field experiments may be used to characterize the mechanisms underlying stellar orientation. © 2018 The Author(s).

  13. Radio observations of candidate magnetic O stars

    NARCIS (Netherlands)

    Schnerr, R.S.; Rygl, K.L.J.; Oosterloo, T.A.; Miller-Jones, J.C.A.; Henrichs, H.F.

    2008-01-01

    A number of O stars are suspected to have (weak) magnetic fields because of the observed cyclical variability in their UV wind-lines. However, direct detections of these magnetic fields with optical spectropolarimetry have proven to be very difficult. We have searched for non-thermal radio emission,

  14. Discovery of the magnetic field in the pulsating B star β Cephei

    NARCIS (Netherlands)

    Henrichs, H.F.; de Jong, J.A.; Verdugo, E.; Schnerr, R.S.; Neiner, C.; Donati, J.-F.; Catala, C.; Shorlin, S.L.S.; Wade, G.A.; Veen, P.M.; Nichols, J.S.; Damen, E.M.F.; Talavera, A.; Hill, G.M.; Kaper, L.; Tijani, A.M.; Geers, V.C.; Wiersema, K.; Plaggenborg, B.; Rygl, K.L.J.

    2013-01-01

    Context. Although the star itself is not helium enriched, the periodicity and the variability in the UV wind lines of the pulsating B1 IV star β Cephei are similar to what is observed in magnetic helium-peculiar B stars, suggesting that β Cep is magnetic. Aims. We searched for a magnetic field using

  15. Four Star School Awards: Key Factors that Predict High Performance among Indiana School Corporations

    Science.gov (United States)

    Veracco, Lawrence H.

    2009-01-01

    The purpose of this study was to analyze the Four Star status of Indiana school corporations in order to determine if certain variables currently existing among school corporations could be predictive of Four Star status. Differences in Four Star status were examined with respect to school corporation size, school corporation average teacher…

  16. 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 ...

  17. Merging strangeon stars

    Science.gov (United States)

    Lai, Xiao-Yu; Yu, Yun-Wei; Zhou, En-Ping; Li, Yun-Yang; Xu, Ren-Xin

    2018-02-01

    The state of supranuclear matter in compact stars remains puzzling, and it is argued that pulsars could be strangeon stars. What would happen if binary strangeon stars merge? This kind of merger could result in the formation of a hyper-massive strangeon star, accompanied by bursts of gravitational waves and electromagnetic radiation (and even a strangeon kilonova explained in the paper). The tidal polarizability of binary strangeon stars is different from that of binary neutron stars, because a strangeon star is self-bound on the surface by the fundamental strong force while a neutron star by the gravity, and their equations of state are different. Our calculation shows that the tidal polarizability of merging binary strangeon stars is favored by GW170817. Three kinds of kilonovae (i.e., of neutron, quark and strangeon) are discussed, and the light curve of the kilonova AT 2017 gfo following GW170817 could be explained by considering the decaying strangeon nuggets and remnant star spin-down. Additionally, the energy ejected to the fireball around the nascent remnant strangeon star, being manifested as a gamma-ray burst, is calculated. It is found that, after a prompt burst, an X-ray plateau could follow in a timescale of 102 ‑ 103 s. Certainly, the results could be tested also by further observational synergies between gravitational wave detectors (e.g., Advanced LIGO) and X-ray telescopes (e.g., the Chinese HXMT satellite and eXTP mission), and especially if the detected gravitational wave form is checked by peculiar equations of state provided by the numerical relativistical simulation.

  18. Are blue supergiants descendants of magnetic main sequence stars?

    Science.gov (United States)

    Petermann, Ilka; Langer, Norbert

    2013-06-01

    Red and blue supergiants are, together with luminous blue variables and Wolf-Rayet stars, evolved phases of massive (OB) stars. The position of blue supergiants (BSG) near the main sequence band cannot be reproduced by standard stellar evolution calculations. However, the assumption of a reduced convective core mass during the main sequence (MS) due to strong internal magnetic fields, established in roughly 10% of all stars on the upper MS, can recover this BSG population. For our calculations of the (non-rotating) massive stars at solar metallicity we used the 1D stellar evolution code MESA and compare their evolutionary tracks with positions from stars obtained from the VLT Flames survey of massive stars.

  19. LAMOST views δ Scuti pulsating stars

    Science.gov (United States)

    Qian, S.-B.; Li, L.-J.; He, J.-J.; Zhang, J.; Zhu, L.-Y.; Han, Z.-T.

    2018-03-01

    About 766 δ Scuti stars were observed by LAMOST by 2017 June 16. Stellar atmospheric parameters of 525 variables were determined, while spectral types were obtained for all samples. In the paper, those spectroscopic data are catalogued. We detect a group of 131 unusual and cool variable stars (UCVs) that are distinguished from the normal δ Scuti stars (NDSTs). On the H-R diagram and the log g-T diagram, the UCVs are far beyond the red edge of pulsational instability trip. Their effective temperatures are lower than 6700 K with periods in the range from 0.09 to 0.22 d. NDSTs have metallicity close to that of the Sun as expected, while UCVs are slightly metal poor than NDSTs. The two peaks on the distributions of the period and stellar atmospheric parameters are all caused by the existence of UCVs. When those UCVs are excluded, it is discovered that the effective temperature, the gravitational acceleration, and the metallicity all are correlated with the pulsating period for NDSTs and their physical properties and evolutionary states are discussed. Detection of those UCVs indicates that about 25 per cent of the known δ Scuti stars may be misclassified. However, if some of them are confirmed to be pulsating stars, they will be a new-type pulsator and their investigations will shed light on theoretical instability domains and on the theories of interacting between the pulsation and the convection of solar-type stars. Meanwhile, 88 δ Scuti stars are detected to be the candidates of binary or multiple systems.

  20. Convective overshooting in stars

    NARCIS (Netherlands)

    Andrássy, R.

    2015-01-01

    Numerous observations provide evidence that the standard picture, in which convective mixing is limited to the unstable layers of a star, is incomplete. The mixing layers in real stars are significantly more extended than what the standard models predict. Some of the observations require changing

  1. Hyperons in neutron stars

    International Nuclear Information System (INIS)

    Glendenning, N.K.

    1986-04-01

    Generalized beta equilibrium involving nucleons, hyperons, and isobars is examined for neutron star matter. The hyperons produce a considerable softening of the equation of state. It is shown that the observed masses of neutron stars can be used to settle a recent controversy concerning the nuclear compressibility. Compressibilities less than 200 MeV are incompatible with observed masses. 7 refs., 9 figs

  2. PAHs and star formation

    NARCIS (Netherlands)

    Tielens, AGGM; Peeters, E; Bakes, ELO; Spoon, HWW; Hony, S; Johnstone, D; Adams, FC; Lin, DNC; Neufeld, DA; Ostriker, EC

    2004-01-01

    Strong IR emission features at 3.3, 6.2, 7.7, 8.6, and 11.2 mum are a common characteristic of regions of massive star formation. These features are carried by large (similar to 50 C-atom) Polycyclic Aromatic Hydrocarbon molecules which are pumped by the strong FUV photon flux from these stars.

  3. Science Through ARts (STAR)

    Science.gov (United States)

    Kolecki, Joseph; Petersen, Ruth; Williams, Lawrence

    2002-01-01

    Science Through ARts (STAR) is an educational initiative designed to teach students through a multidisciplinary approach to learning. This presentation describes the STAR pilot project, which will use Mars exploration as the topic to be integrated. Schools from the United Kingdom, Japan, the United States, and possibly eastern Europe are expected to participate in the pilot project.

  4. Neutron Stars and Pulsars

    CERN Document Server

    Becker, Werner

    2009-01-01

    Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

  5. Rotating stars in relativity.

    Science.gov (United States)

    Paschalidis, Vasileios; Stergioulas, Nikolaos

    2017-01-01

    Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on equilibrium properties and on nonaxisymmetric oscillations and instabilities in f -modes and r -modes have been updated. Several new sections have been added on equilibria in modified theories of gravity, approximate universal relationships, the one-arm spiral instability, on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity including both hydrodynamic and magnetohydrodynamic studies of these objects.

  6. 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.

  7. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Energy Technology Data Exchange (ETDEWEB)

    Theodorakis, P E [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Avgeropoulos, A [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Universidad Nacional de Educacion a Distancia, Facultad de Ciencias, Senda del Rey 9, 28040 Madrid (Spain); Kosmas, M [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece); Vlahos, C [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece)

    2007-11-21

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  8. A Tale of Two Cataclysmic Earthquakes: 39 and 52 kyr BP, Dead Sea Transform, Israel; a Multi-archive Study

    Science.gov (United States)

    Kagan, E. J.; Stein, M.; Bar-Matthews, M.; Agnon, A.

    2007-12-01

    well as five well-constrained collapses in different areas of the Soreq cave. The ~52±2 ka seismic event has left evidence at M1b (a closely spaced doublet of seismites), at PZ1 (followed by a period with numerous (8) and very thick (up to 48 cm) seismites) and at the cave site (3 collapses). We suggest that these seismic events are large-earthquakes, sufficiently strong to cause cave collapses and lake bottom brecciation in numerous and distant sites in very different kinds of sediments. We suggest that these large events are representatives of the largest magnitude earthquakes in the Dead Sea region. We extrapolate the frequency-size statistics from the instrumental data using a power-law (Gutenberg-Richter) to estimate ranges of magnitude for these cataclysmic events.

  9. Star Cluster Structure from Hierarchical Star Formation

    Science.gov (United States)

    Grudic, Michael; Hopkins, Philip; Murray, Norman; Lamberts, Astrid; Guszejnov, David; Schmitz, Denise; Boylan-Kolchin, Michael

    2018-01-01

    Young massive star clusters (YMCs) spanning 104-108 M⊙ in mass generally have similar radial surface density profiles, with an outer power-law index typically between -2 and -3. This similarity suggests that they are shaped by scale-free physics at formation. Recent multi-physics MHD simulations of YMC formation have also produced populations of YMCs with this type of surface density profile, allowing us to narrow down the physics necessary to form a YMC with properties as observed. We show that the shallow density profiles of YMCs are a natural result of phase-space mixing that occurs as they assemble from the clumpy, hierarchically-clustered configuration imprinted by the star formation process. We develop physical intuition for this process via analytic arguments and collisionless N-body experiments, elucidating the connection between star formation physics and star cluster structure. This has implications for the early-time structure and evolution of proto-globular clusters, and prospects for simulating their formation in the FIRE cosmological zoom-in simulations.

  10. JetStar in flight

    Science.gov (United States)

    1981-01-01

    aircraft provided far-field acoustic data. Between May 21, 1981 and August of 1982, the JetStar completed roughly 45 research flights with three different propellers in varying configurations. Dryden engineers analyzed some of the resultant data, while they sent flight tapes to Hamilton Standard, Lewis, and Langley for analysis there. The results indicated a need for noise-reduction technology to keep the noise levels down to the project goals. An improved version of the advanced turboprop underwent flight testing in 1987 on a Gulfstream II over Georgia in 1987. These flight tests verified predictions of a 20- to 30-percent fuel savings. However, with the end of the energy crisis, the need for such savings disappeared, and the Advanced Turboprop Project did not lead to the expected industry-wide adoption of the new propeller systems on transport aircraft. In the 1960s, the same JetStar that was used to test the advanced turboprop had been equipped with an electronic variable-stability flight-control system. Called then a General Purpose Airborne Simulator (GPAS), the aircraft could duplicate the flight characteristics of a wide variety of advanced aircraft and was used for supersonic transport and general aviation research, and as a training and support system for Space Shuttle Approach and Landing Tests at Dryden in 1977. Over the years, the JetStar has also been used for a variety of other flight research projects, including laminar-flow-control flight tests in the mid-1980s.

  11. Dense Axion Stars.

    Science.gov (United States)

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-16

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10^{-14}M_{⊙} if the axion mass is 10^{-4}  eV. We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10^{-20}M_{⊙} to about M_{⊙}. If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  12. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  13. Infrared spectroscopy of stars

    Science.gov (United States)

    Merrill, K. M.; Ridgway, S. T.

    1979-01-01

    This paper reviews applications of IR techniques in stellar classification, studies of stellar photospheres, elemental and isotopic abundances, and the nature of remnant and ejected matter in near-circumstellar regions. Qualitative IR spectral classification of cool and hot stars is discussed, along with IR spectra of peculiar composite star systems and of obscured stars, and IR characteristics of stellar populations. The use of IR spectroscopy in theoretical modeling of stellar atmospheres is examined, IR indicators of stellar atmospheric composition are described, and contributions of IR spectroscopy to the study of stellar recycling of interstellar matter are summarized. The future of IR astronomy is also considered.

  14. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2007-01-01

    Thermonuclear reactions in stars is a major topic in the field of nuclear astrophysics, and deals with the topics of how precisely stars generate their energy through nuclear reactions, and how these nuclear reactions create the elements the stars, planets and - ultimately - we humans consist of. The present book treats these topics in detail. It also presents the nuclear reaction and structure theory, thermonuclear reaction rate formalism and stellar nucleosynthesis. The topics are discussed in a coherent way, enabling the reader to grasp their interconnections intuitively. The book serves bo

  15. An observational study of post-asymptotic-giant-branch stars

    Science.gov (United States)

    Sahin, T.

    2008-05-01

    -AGB stars. We detected helium enrichment in the post-AGB stars Hen3-1428 and LSS4331. We did not detect any evidence of s-process elements, primarily because of the high Teff of our targets. Our results do not show overabundance in phosphorus for any hot pAGB stars. Since we used the same atomic data and methods, we conclude that the enhancement of phosphorus previously found in some EHe stars is real. We studied stellar wind signatures for the post-AGB star LSIV-12 111. Emission line equivalent widths for Balmer lines show changes between two different epochs. Hen3-1428 and LSIV-12 111 show blue shifted absorption lines. A stellar wind is clearly present in both stars. We compared variability of a group of post-AGB and a group EHe stars using archival photometry. We did not detect variability in EHe stars. We detected variability in five post-AGB stars. Large variations in HR4049, HD213985, and HD52961 appear to be related to the binary period.

  16. Pulsating stars in ω Centauri. Near-IR properties and period-luminosity relations

    Directory of Open Access Journals (Sweden)

    Navarrete Camila

    2017-01-01

    Full Text Available ω Centauri (NGC 5139 contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR variability survey of ω Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete J and KS near-IR catalog of variable stars in the field of ω Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands.

  17. Rotational properties of magnetic chemically peculiar stars

    Science.gov (United States)

    Netopil, M.; Paunzen, E.; Hümmerich, S.; Bernhard, K.

    2018-01-01

    The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit strong and globally organized magnetic fields that are inclined to the rotational axis and facilitate the development of surface abundance inhomogeneities resulting in photometric and spectroscopic variability. Photometric time series data are much easier to obtain than spectroscopic/polarimetric data or are available from large surveys, thus the number of known rotational periods increased significantly during the last years. Furthermore, Gaia data allow us to place an unprecedentedly large sample of mCP stars in the Hertzsprung-Russell diagram and to investigate evolutionary effects. In this paper we review the rotational properties of mCP stars and discuss open issues of stellar rotation in the presence of strong magnetic fields.

  18. XSS J00564+4548 and IGR J00234+6141: New cataclysmic variables from the RXTE and INTEGRAL all-sky surveys

    Science.gov (United States)

    Bikmaev, I. F.; Revnivtsev, M. G.; Burenin, R. A.; Sunyaev, R. A.

    2006-09-01

    We present the results of our optical identification of two X-ray sources from the RXTE and INTEGRAL all-sky surveys: XSS J00564+4548 and IGR J00234+6141. Using optical observations with the 1.5-m Russian-Turkish Telescope (RTT150) and publicly accessible X-ray data from the SWIFT Orbital Observatory, we show that these sources are most likely intermediate polars, i.e., binary systems with accreting white dwarfs that possess a moderately strong magnetic field (≲10 MG). We have found periodic optical oscillations with periods of ≈480 and ≈570 s. These periods most likely correspond to the rotation periods of the white dwarfs in these systems. Further optical RTT150 observations of these systems will allow their parameters to be studied in more detail.

  19. Carbon Stars T. Lloyd Evans

    Indian Academy of Sciences (India)

    that the features used in estimating luminosities of ordinary giant stars are just those whose abundance ... This difference between the spectral energy distributions (SEDs) of CH stars and the. J stars, which belong to .... that the first group was binaries, as for the CH stars of the solar vicinity, while those of the second group ...

  20. Neutron Stars : Magnetism vs Gravity

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Neutron Stars : Magnetism vs Gravity. WHY do neutron stars have such strong magnetic fields? Conservation of magnetic flux of the collapsing stellar core. ∫ B.ds (over surface of the star) = constant; Radius of the star collapses from ~ 5x108 to 1x104 metres; Hence, ...