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Sample records for cataclysmic variable stars

  1. ULTRACAM photometry of eclipsing cataclysmic variable stars

    CERN Document Server

    Feline, William James

    2008-01-01

    The accurate determination of the masses of cataclysmic variable stars is critical to our understanding of their origin, evolution and behaviour. Observations of cataclysmic variables also afford an excellent opportunity to constrain theoretical physical models of the accretion discs housed in these systems. In particular, the brightness distributions of the accretion discs of eclipsing systems can be mapped at a spatial resolution unachievable in any other astrophysical situation. This thesis addresses both of these important topics via the analysis of the light curves of six eclipsing dwarf novae, obtained using ULTRACAM, a novel high-speed imaging photometer.

  2. On the eclipsing cataclysmic variable star HBHA 4705-03

    CERN Document Server

    Rutkowski, A; Marsh, T R; Eker, Z

    2013-01-01

    We present observations and analysis of a new eclipsing binary HBHA 4705-03. Using decomposition of the light curve into accretion disk and hot spot components, we estimated photometrically the mass ratio of the studied system to be q=0.62 +-0.07. Other fundamental parameters was found with modeling. This approach gave: white dwarf mass M_1 = (0.8 +- 0.2) M_sun, secondary mass M_2=(0.497 +- 0.05) M_sun, orbital radius a=1.418 R_sun, orbital inclination i = (81.58 +- 0.5) deg, accretion disk radius r_d/a = 0.366 +- 0.002, and accretion rate dot{M} = (2.5 +- 2) * 10^{18}[g/s], (3*10^{-8} [M_sun/yr]). Power spectrum analysis revealed ambiguous low-period Quasi Periodic Oscillations centered at the frequencies f_{1}=0.00076 Hz, f_2=0.00048 Hz and f_3=0.00036 Hz. The B-V=0.04 [mag] color corresponds to a dwarf novae during an outburst. The examined light curves suggest that HBHA 4705-03 is a nova-like variable star.

  3. SW Sex stars, old novae, and the evolution of cataclysmic variables

    CERN Document Server

    Schmidtobreick, Linda

    2014-01-01

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

  4. Dwarf nova-type cataclysmic variable stars are significant radio emitters

    CERN Document Server

    Coppejans, Deanne L; Miller-Jones, James C A; Rupen, Michael P; Sivakoff, Gregory R; Knigge, Christian; Groot, Paul J; Woudt, Patrick A; Waagen, Elizabeth O; Templeton, Matthew

    2016-01-01

    We present 8--12\\,GHz radio light curves of five dwarf nova (DN) type Cataclysmic Variable stars (CVs) in outburst (RX And, U Gem and Z Cam), or superoutburst (SU UMa and YZ Cnc), increasing the number of radio-detected DN by a factor of two. The observed radio emission was variable on time-scales of minutes to days, and we argue that it is likely to be synchrotron emission. This sample shows no correlation between the radio luminosity and optical luminosity, orbital period, CV class, or outburst type; however higher-cadence observations are necessary to test this, as the measured luminosity is dependent on the timing of the observations in these variable objects. The observations show that the previously detected radio emission from SS Cyg is not unique in type, luminosity (in the plateau phase of the outburst), or variability time-scales. Our results prove that DN, as a class, are radio emitters in outburst.

  5. Abundance Derivations for the Secondary Stars in Cataclysmic Variables from Near-Infrared Spectroscopy

    CERN Document Server

    Harrison, Thomas E

    2016-01-01

    We derive metallicities for 41 cataclysmic variables (CVs) from near-infrared spectroscopy. We use synthetic spectra that cover the 0.8 $\\mu$m $\\leq \\lambda \\leq$ 2.5 $\\mu$m bandpass to ascertain the value of [Fe/H] for CVs with K-type donors, while also deriving abundances for other elements. Using calibrations for determining [Fe/H] from the $K$-band spectra of M-dwarfs, we derive more precise values for T$_{\\rm eff}$ for the secondaries in the shortest period CVs, and examine whether they have carbon deficits. In general, the donor stars in CVs have sub-solar metallicities. We confirm carbon deficits for a large number of systems. CVs with orbital periods $>$ 5 hr are most likely to have unusual abundances. We identify four CVs with CO emission. We use phase-resolved spectra to ascertain the mass and radius of the donor in U Gem. The secondary star in U Gem appears to have a lower {\\it apparent} gravity than a main sequence star of its spectral type. Applying this result to other CVs, we find that the late...

  6. Infrared Spectroscopic Observations of the Secondary Stars of Short Period Sub-Gap Cataclysmic Variables

    CERN Document Server

    Hamilton, Ryan T; Tappert, Claus; Howell, Steve B

    2010-01-01

    We present K-band spectroscopy of short period, "sub-gap" cataclysmic variable (CV) systems obtained using ISAAC on the VLT. We show the infrared spectra (IR) for nine systems below the 2-3 hour period gap: V2051 Oph, V436 Cen, EX Hya, VW Hyi, Z Cha, WX Hyi, V893 Sco, RZ Leo, and TY PsA. We are able to clearly detect the secondary star in all but WX Hyi, V893 Sco, and TY PsA. We present the first direct detection of the secondary stars of V2051 Oph, V436 Cen, and determine new spectral classifications for EX Hya, VW Hyi, Z Cha, and RZ Leo. We find that the CO band strengths of all but Z Cha appear normal for their spectral types, in contrast to their longer period cousins above the period gap. This brings the total number of CVs and pre-CVs with moderate resolution (R >~ 1500) IR spectroscopy to sixty-one systems: nineteen pre-CVs, thirty-one non-magnetic systems, and eleven magnetic or partially magnetic systems. We discuss the trends seen in the IR abundance patterns thus far, and highlight a potential link...

  7. Long-term Accretion Variations of the Magnetic Cataclysmic Variable Star QQ Vulpecula

    Science.gov (United States)

    Cooper Rose, Sanaea; Kafka, Stella; Jorgenson, Regina; Carr, Derrick; Childs, Francesca; Christenson, Holly; Karim, Md. Tanveer; Konchady, Tarini; Walker, Gary E.; Honeycutt, R. K.

    2017-01-01

    Magnetic cataclysmic variable stars have brightness variations that repeat with each revolution of the two stars about the center of mass of the system. However, in the case of QQ Vulpecula (QQ Vul), this brightness variation pattern changes in the long term. This study makes use of two decades worth of data from the Roboscope Telescope as well as data from the American Association of Variable Star Observers (AAVSO) database to examine the long-term evolution of QQ Vul’s phase curves. Nightly observations using the Maria Mitchell Association's Vestal and Loines Observatories supplemented this analysis by clarifying short-term brightness variation. The long-term data was divided into four commonly observed behavioral types ranging from a double peaked curve of ~15.5 magnitude to a ~15.0 magnitude curve that had a primary minimum and a slow, linear rise in brightness in place of the secondary minimum. The nightly data kept within the confines of these categories, though the secondary minimum in the nightly data never vanished. No periodicity was found in the long-term variations. The model often invoked to explain the double peaked curve consists of single pole accretion in which a partial self-eclipse causes the secondary minimum and cyclotron beaming causes the primary minimum. However, the long-term variation may indicate a changing accretion rate, which may manifest itself in changes to the shape, size, or location of the accretion spot on the white dwarf such that it lessens or removes the secondary minimum. This project was supported by the NSF REU grant AST-1358980, the Massachusetts Space Grant, and the Nantucket Maria Mitchell Association.

  8. The Eclipsing Cataclysmic Variable Lanning 386: Dwarf Nova, SW Sextantis Star, or Both?

    OpenAIRE

    Brady, S; Thorstensen, J.R.; Koppelman, M. D.; Prieto, J. L.; Garnavich, P. M.; Hirschauer, A.; Florack, M.

    2008-01-01

    We present photometry and spectroscopy of the suspected cataclysmic variable (CV) Lanning 386. We confirm that it is a CV, and observe deep eclipses, from which we determine the orbital period Porb to be 0.1640517 +- 0.0000001 d (= 3.94 h). Photometric monitoring over two observing seasons shows a very active system with frequent outbursts of variable amplitude, up to approx. 2 mag. The spectrum in quiescence is typical of dwarf novae, but in its high state the system shows strong HeII emissi...

  9. Full 3-D MHD calculations of accretion flow Structure in magnetic cataclysmic variable stars with strong and complex magnetic fields

    CERN Document Server

    Zhilkin, A G; Mason, P A; 10.1134/S1063772912040087

    2012-01-01

    We performed 3D MHD calculations of stream accretion in cataclysmic variable stars for which the white dwarf primary star possesses a strong and complex magnetic field. These calculations are motivated by observations of polars; cataclysmic variables containing white dwarfs with magnetic fields sufficiently strong to prevent the formation of an accretion disk. So an accretion stream flows from the L1 point and impacts directly onto one or more spots on the surface of the white dwarf. Observations indicate that the white dwarf, in some binaries, possesses a complex (non-dipolar) magnetic field. We perform simulations of 10 polars or equivalently one asynchronous polar at 10 different beat phases. Our models have an aligned dipole plus quadrupole magnetic field centered on the white dwarf primary. We find that for a sufficiently strong quadrupole component an accretion spot occurs near the magnetic equator for slightly less than half of our simulations while a polar accretion zone is active for most of the rest...

  10. Curious Variables Experiment (CURVE). IX Draconis - a Clue for Understanding Evolution of Cataclysmic Variable Stars

    CERN Document Server

    Olech, A; Mularczyk, K; Kedzierski, P; Wisniewski, M; Stachowski, G

    2004-01-01

    We report extensive photometry of frequently outbursting dwarf nova IX Draconis. During five months of observations the star went into three superoutbursts and seven ordinary outbursts. This allowed us to determine its supercycle and cycle lengths as equal to 54 +/- 1 and 3.1 +/- 0.1 days, respectively. During the Sep 2003 superoutburst, which had the best observational coverage, IX Dra displayed clear superhumps with a period of Psh=0.066968(17) days. This period was constant during the whole superoutburst. Another period, which was clearly present in the light curve of IX Dra in superoutburst, had a value of 0.06646(6) days and we interpret it as the orbital period of the binary. Thus IX Dra is the first SU UMa star showing orbital modulation during the entire superoutburst. The beat between these two periods is the main cause of an unusual phase reversal of superhumps - a phenomenon which was previously observed in ER UMa. If our interpretation of the second periodicity is correct, IX Dra has an extremely ...

  11. Mass transfer cycles in cataclysmic variables

    Science.gov (United States)

    King, A. R.; Frank, J.; Kolb, U.; Ritter, H.

    1995-01-01

    It is well known that in cataclysmic variables the mass transfer rate must fluctuate about the evolutionary mean on timescales too long to be directly observable. We show that limit-cycle behavior can occur if the radius change of the secondary star is sensitive to the instantaneous mass transfer rate. The only reasonable way in which such a dependence can arise is through irradiation of this star by the accreting component. The system oscillates between high states, in which irradiation causes slow expansion of the secondary and drives an elevated transfer rate, and low states, in which this star contracts.

  12. Herschel Observations of Cataclysmic Variables

    CERN Document Server

    Harrison, Thomas E; Tappert, Claus; Hoffman, Douglas I; Campbell, Ryan K

    2012-01-01

    We have used the PACS instrument on the Herschel Space Observatory to observe eight cataclysmic variables at 70 and 160 microns. Of these eight objects, only AM Her was detected. We have combined the Herschel results with ground-based, Spitzer, and WISE observations to construct spectral energy distributions for all of the targets. For the two dwarf novae in the sample, SS Cyg and U Gem, we find that their infrared luminosities are completely dominated by their secondary stars. For the two highly magnetic "polars" in our survey, AM Her and EF Eri, we find that their mid-infrared excesses, previously attributed to circumbinary dust emission, can be fully explained by cyclotron emission. The WISE light curves for both sources show large, orbitally modulated variations that are identically phased to their near-IR light curves. We propose that significant emission from the lowest cyclotron harmonics (n

  13. The winds of cataclysmic variables

    Energy Technology Data Exchange (ETDEWEB)

    Mauche, C.W. [Lawrence Livermore National Lab., CA (United States). Lab. for Experimental Astrophysics; Raymond, J.C. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)

    1994-02-16

    The authors present an observational and theoretical review of the winds of cataclysmic variables (CVs). Specifically, they consider the related problems of the geometry and mass-loss rate of the winds of CVs, their ionization state and variability, and the results from studies of eclipsing CVs. Finally, they consider the properties of accretion disk wind models. Some of these models predict substantial angular momentum loss, which could affect both disk structure and binary evolution.

  14. Unambiguous Detection of Reflection in Magnetic Cataclysmic Variables: Joint NuSTAR-XMM-Newton Observations of Three Intermediate Polars

    CERN Document Server

    Mukai, Koji; Bernardini, Federico; de Martino, Domitilla

    2015-01-01

    In magnetic cataclysmic variables (CVs), X-ray emission regions are located close to the white dwarf surface, which is expected to reflect a significant fraction of intrinsic X-rays above 10 keV, producing a Compton reflection hump. However, up to now, a secure detection of this effect in magnetic CVs has largely proved elusive because of the limited sensitivity of non-imaging X-ray detectors. Here we report our analysis of joint NuSTAR/XMM-Newton observations of three magnetic CVs, V709 Cas, NY Lup, and V1223 Sgr. The improved hard X-ray sensitivity of the imaging NuSTAR data has resulted in the first robust detection of Compton hump in all three objects, with amplitudes of ~1 or greater in NY Lup, and likely <1.0 in the other two. We also confirm earlier report of a strong spin modulation above 10 keV in V709 Cas, and report the first detection of small spin amplitudes in the others. We interpret this as due to different height of the X-ray emitting region among these objects. A height of ~0.2 white dwar...

  15. Cataclysmic Variables: Eight Breakthroughs in Eight Years

    CERN Document Server

    Knigge, Christian

    2011-01-01

    The last few years have seen tremendous progress in our understanding of cataclysmic variable stars. As a result, we are finally developing a much clearer picture of their evolution as binary systems, the physics of the accretion processes powering them, and their relation to other compact accreting objects. In this review, I will highlight some of the most exciting recent breakthroughs. Several of these have opened up completely new avenues of research that will probably lead to additional major advances over the next decade.

  16. K-Band Spectroscopy of (Pre-)Cataclysmic Variables: Are Some Donor Stars Really Carbon Poor?

    CERN Document Server

    Howell, Steve B; Szkody, Paula; Silvestri, Nicole M

    2010-01-01

    We present a new sample of $K$-band spectral observations for CVs: non-magnetic and magnetic as well as present day and pre CVs. The purpose of this diverse sample is to address the recent claim that the secondary stars in dwarf novae are carbon deficient, having become so through a far more evolved evolution than the current paradigm predicts. Our new observations, along with previous literature results, span a wide range of orbital period and CV type. In general, dwarf novae in which the secondary star is seen show weak to no CO absorption while polar and pre-CV donor stars appear to have normal CO absorption for their spectral type. However, this is not universal. The presence of normal looking CO absorption in the dwarf nova SS Aur and the hibernating CV QS Vir and a complete lack of CO absorption in the long period polar V1309 Ori cloud the issue. A summary of the literature pointing to non-solar abundances including enhanced NV/CIV ratios is presented. It appears that some CVs have non-solar abundance m...

  17. White dwarfs in cataclysmic variables

    Science.gov (United States)

    Gaensicke, Boris

    2016-07-01

    Cataclysmic variables (CVs) provide excellent laboratories to study the effect that the accretion of matter, energy and angular momentum has on the structure of white dwarfs, with important implications on the evolution of these compact binaries, the ignition of thermonuclear surface burning, and potentially their explosion as SNIa. I will provide an overview of our current understanding of CV white dwarfs, with a particular emphasis on the results of a recent large HST program. I will review our knowledge regarding the mass distribution of CV white dwarfs, as well as the secular mean accretion rates that can be inferred from their effective temperatures, and compare those statistics with predictions from CV population models. I will also discuss a sub-set of CVs which underwent thermal-time scale mass transfer, one of the channels that is often discussed as a pathway to SN Ia, and I will illustrate how the study of these "failed SNIa" can contribute to the discussion of SNIa progenitors. Finally, I will discuss the occurrence of non-radial pulsations in white dwarfs, both in CVs and their detached progenitors.

  18. Cataclysmic variables and related objects; Proceedings of the Seventy-second Colloquium, Haifa, Israel, August 9-13, 1982

    Science.gov (United States)

    Livio, M.; Shaviv, G.

    The periods of cataclysmic variable stars are considered along with photometric and spectroscopic observations of the cataclysmic variable AC Cancri, recent spectroscopy of X-ray sources and systems related to cataclysmic variables, orbital solutions for WZ Sagittae during quiescence, spectra of symbiotic stars, and the formation of optical CNO emission lines in cataclysmic variables. Attention is given to infrared spectra of nova dust shells, evolutionary models for SNI progenitor stars, the physical conditions inside white dwarfs and type I supernovae, the energy distribution of hard X-ray emitting cataclysmic variables, time dependence in accretion onto magnetic white dwarfs, polarized radiation from AM Herculis stars, and radio emission and synchronization. Other topics discussed are related to X-ray emission from cataclysmic variables, mass loss associated with X-ray bursts of neutron stars, and fast oscillations in variable X-ray sources and X-ray bursters. For individual items see A84-35927 to A84-35954

  19. Observations of Faint Eclipsing Cataclysmic Variables

    CERN Document Server

    Çamurdan, Dicle Zengin; Çamurdan, C Muzaffer

    2010-01-01

    We present time-resolved photometry of six faint (V>17mag) cataclysmic variables (CVs); one of them is V849 Oph and the others are identified from the Sloan Digital Sky Survey (SDSS J0920+0042, SDSS J1327+6528, SDSS J1227+5139, SDSS J1607.02+3623, SDSS J1457+5148). The optical CCD photometric observations of these objects were performed at the T\\"UB\\.ITAK National Observatory (Turkey) between February 2006 and March 2009. We aimed to detect short time scale orbital variability arisen from hot-spot modulation, flickering structures which occur from rapid fluctuations of material transferring from red star to white dwarf and orbital period changes for selected short-period (P<4h) CVs at quiescence. Results obtained from eclipse timings and light curves morphology related to white dwarf stars, accretion disks and hot-spots are discussed for each system. Analysis of the short time coverage of data, obtained for SDSS J1227+5139 indicates a cyclical period change arisen from magnetic activity on the secondary st...

  20. Cataclysmic Variables from SDSS III. The Third Year

    CERN Document Server

    Szkody, P; Fraser, O J; Silvestri, N M; Bochanski, J J; Wolfe, M A; Agüeros, M A; Warner, B; Woudt, P; Tramposch, J; Homer, L; Schmidt, G; Knapp, G R; Anderson, S F; Covey, K; Harris, H; Hawley, S; Schneider, D P; Voges, W; Brinkmann, J; Szkody, Paula; Henden, Arne; Fraser, Oliver; Silvestri, Nicole; Bochanski, John; Wolfe, Michael A.; Ag\\"ueros, Marcel; Warner, Brian; Woudt, Patrick; Tramposch, Jonica; Homer, Lee; Schmidt, Gary; Knapp, Gillian R.; Anderson, Scott F.; Covey, Kevin; Harris, Hugh; Hawley, Suzanne; Schneider, Donald P.; Voges, Wolfgang

    2004-01-01

    This paper continues the series that identifies new cataclysmic variables found in the Sloan Digital Sky Survey. We present 36 cataclysmic variables and one possible symbiotic star from Sloan spectra obtained during 2002, of which 34 are new discoveries, 2 are known dwarf novae (BC UMa, KS UMa) and one is a known CV identified from the 2dF survey. The positions, colors and spectra of all 37 systems are presented, along with follow-up spectroscopic/photometric observations of 10 systems. As in the past 2 years of data, the new SDSS systems show a large variety of characteristics based on their inclination and magnetic fields, including 3 eclipsing systems, 4 with prominent He II emission, and 15 systems showing features of the underlying stars.

  1. White dwarf masses in cataclysmic variables

    CERN Document Server

    Wijnen, T P G; Schreiber, M R

    2015-01-01

    The white dwarf (WD) mass distribution of cataclysmic variables (CVs) has recently been found to dramatically disagree with the predictions of the standard CV formation model. The high mean WD mass among CVs is not imprinted in the currently observed sample of CV progenitors and cannot be attributed to selection effects. Two possibilities have been put forward: either the WD grows in mass during CV evolution, or in a significant fraction of cases, CV formation is preceded by a (short) phase of thermal time-scale mass transfer (TTMT) in which the WD gains a sufficient amount of mass. We investigate if either of these two scenarios can bring theoretical predictions and observations into agreement. We employed binary population synthesis models to simulate the present intrinsic CV population. We incorporated aspects specific to CV evolution such as an appropriate mass-radius relation of the donor star and a more detailed prescription for the critical mass ratio for dynamically unstable mass transfer. We also imp...

  2. Realistic MHD Modelling of Cataclysmic Variable Spin-Down

    Science.gov (United States)

    Lascelles, Alex; Garraffo, Cecilia; Drake, Jeremy J.; Cohen, Ofer

    2017-01-01

    The orbital evolution of cataclysmic variables with periods above the "period gap" (>3 hrs) is governed by angular momentum loss via the magnetized wind of the unevolved secondary star. The usual prescription to study such systems takes into account only the magnetic field of the secondary and assumes its field is dipolar. It has been shown that introduction of the white dwarf and its magnetic field can significantly impact the wind’s structure, leading to a change in angular momentum loss rate and evolutionary timescale by an order of magnitude. Furthermore, the complexity of the magnetic field can drastically alter stellar spin-down rates. We explore the effects of orbital separation and magnetic field configuration on mass and angular momentum loss rates through 3-D magnetohydrodynamic simulations. We present the results of a study of cataclysmic variable orbital evolution including these new ingredients.

  3. 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.

  4. NSV 1907 - A new eclipsing, nova-like cataclysmic variable

    CERN Document Server

    Hümmerich, Stefan; Hambsch, Franz-Josef; Dubois, Franky; Ashley, Richard; Gänsicke, Boris T; Vanaverbeke, Siegfried; Bernhard, Klaus; Wils, Patrick

    2016-01-01

    NSV 1907, formerly listed as an irregular variable in variability catalogues, was classified as an Algol-type eclipsing binary in the Catalina Surveys Periodic Variable Star Catalogue. We have identified NSV 1907 as an ultraviolet (UV) bright source using measurements from the GALEX space telescope and detected obvious out-of-eclipse variability in archival photometric data from the Catalina Sky Survey, which instigated a closer examination of the object. A spectrum and extensive multicolour photometric observations were acquired, from which we deduce that NSV 1907 is a deeply eclipsing, nova-like cataclysmic variable. Apart from the orbital variations (deep eclipses with a period of P ~ 6.63 hours), changes in mean brightness and irregular short-term variability (flickering) were observed. The presence of a secondary minimum at phase phi ~ 0.5 was established, which indicates a significant contribution of the companion star to the optical flux of the system. We find possible evidence for sinusoidal variation...

  5. 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.

  6. Novalike Cataclysmic Variables in the Infrared

    CERN Document Server

    Hoard, D W; Howell, Steve B; Wachter, Stefanie; Brinkworth, Carolyn S; Knigge, Christian; Drew, J E; Szkody, Paula; Kafka, S; Belle, Kunegunda; Ciardi, David R; Froning, Cynthia S; van Belle, Gerard T; Pretorius, M L

    2014-01-01

    Novalike cataclysmic variables have persistently high mass transfer rates and prominent steady state accretion disks. We present an analysis of infrared observations of twelve novalikes obtained from the Two Micron All Sky Survey, the Spitzer Space Telescope, and the Wide-field Infrared Survey Explorer All Sky Survey. The presence of an infrared excess at >3-5 microns over the expectation of a theoretical steady state accretion disk is ubiquitous in our sample. The strength of the infrared excess is not correlated with orbital period, but shows a statistically significant correlation (but shallow trend) with system inclination that might be partially (but not completely) linked to the increasing view of the cooler outer accretion disk and disk rim at higher inclinations. We discuss the possible origin of the infrared excess in terms of emission from bremsstrahlung or circumbinary dust, with either mechanism facilitated by the mass outflows (e.g., disk wind/corona, accretion stream overflow, and so on) present...

  7. NSV 1907 - A new eclipsing, nova-like cataclysmic variable

    Science.gov (United States)

    Hümmerich, Stefan; Gröbel, Rainer; Hambsch, Franz-Josef; Dubois, Franky; Ashley, Richard; Gänsicke, Boris T.; Vanaverbeke, Siegfried; Bernhard, Klaus; Wils, Patrick

    2017-01-01

    NSV 1907, formerly listed as an irregular variable in variability catalogues, was classified as an Algol-type eclipsing binary in the Catalina Surveys Periodic Variable Star Catalogue. We have identified NSV 1907 as an ultraviolet (UV) bright source using measurements from the GALEX space telescope and detected obvious out-of-eclipse variability in archival photometric data from the Catalina Sky Survey, which instigated a closer examination of the object. A spectrum and extensive multicolour photometric observations were acquired, from which we deduce that NSV 1907 is a deeply eclipsing, nova-like cataclysmic variable. Apart from the orbital variations (deep eclipses with a period of P ≈ 6.63 hours), changes in mean brightness and irregular short-term variability (flickering) were observed. The presence of a secondary minimum at phase φ ≈ 0.5 was established, which indicates a significant contribution of the companion star to the optical flux of the system. We find possible evidence for sinusoidal variations with a period of P ≈ 4.2 d, which we interpret as the nodal precession period of the accretion disc. No outbursts or VY Scl-like drops in brightness were detected either by the CSS or during our photometric monitoring. Because of its spectral characteristics and the observed variability pattern, we propose NSV 1907 as a new moderately bright long-period SW Sextantis star. Further photometric and spectroscopic observations are encouraged.

  8. Searching for nova shells around cataclysmic variables

    CERN Document Server

    Sahman, D I; Knigge, C; Marsh, T R

    2015-01-01

    We present the results of a search for nova shells around 101 cataclysmic variables (CVs), using Halpha images taken with the 4.2-m William Herschel Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric Halpha 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 approx.2.5 arcmin, indicative of a nova eruption approximately 120 years 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 4 asynchronous polars, but found no new shells around an...

  9. Novalike Cataclysmic Variables are Significant Radio Emitters

    CERN Document Server

    Coppejans, Deanne L; Miller-Jones, James C A; Rupen, Michael P; Knigge, Christian; Sivakoff, Gregory R; Groot, Paul J

    2015-01-01

    Radio emission from non-magnetic cataclysmic variables (CVs, accreting white dwarfs) could allow detailed studies of outflows and possibly accretion flows in these nearby, numerous and non-relativistic compact accretors. Up to now, however, very few CVs have been detected in the radio. We have conducted a VLA pilot survey of four close and optically-bright novalike CVs at 6 GHz, detecting three, and thereby doubling the number of radio detections of these systems. RW Sex, V603 Aql and the old nova TT Ari were detected in both of the epochs, while V1084 Her was not detected (to a $3\\sigma$ upper-limit of 7.8 $\\mu\\rm{Jy}\\,\\rm{beam}^{-1}$). These observations clearly show that the sensitivity of previous surveys was typically too low to detect these objects and that non-magnetic CVs can indeed be significant radio emitters. The three detected sources show a range of properties, including flaring and variability on both short ($\\sim$200 s) and longer-term (days) time-scales, as well as circular polarization level...

  10. The Magnetospheric Boundary in Cataclysmic Variables

    CERN Document Server

    Hellier, Coel

    2013-01-01

    The magnetic cataclysmic variables (MCVs) present a wealth of observational diagnostics for studying accretion flows interacting with a magnetosphere. Spin-period pulsations from the rotation of the white dwarf are seen in optical light, in the UV and X-ray bands, and in polarimetry, and modelling these can constrain the size and location of the accretion footprints on the white-dwarf surface. Tracing these back along field lines can tell us about the transition region between the stream or disk and the magnetosphere. Further, optical emission lines give us velocity information, while analysis of eclipses gives spatial information. I discuss MCVs (particularly FO Aqr, V405 Aur, XY Ari and EX Hya, but also mentioning PQ Gem, GK Per, V2400 Oph, HT Cam, TX Col, AO Psc, AE Aqr, WZ Sge, V1223 Sgr and DQ Her), reviewing what observations tell us about the disk-magnetosphere boundary. The spin-period variations are caused by a mixture of geometric effects and absorption by the accretion flow, and appear to show that...

  11. Cataclysmic variables in the SUPERBLINK proper motion survey

    Energy Technology Data Exchange (ETDEWEB)

    Skinner, Julie N.; Thorstensen, John R. [Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755-3528 (United States); Lépine, Sébastien, E-mail: jns@dartmouth.edu [Department of Physics and Astronomy, Georgia State University, 25 Park Place NE, Atlanta, GA 30303 (United States)

    2014-12-01

    We have discovered a new high proper motion cataclysmic variable (CV) in the SUPERBLINK proper motion survey, which is sensitive to stars with proper motions greater than 40 mas yr{sup −1}. This CV was selected for follow-up observations as part of a larger search for CVs selected based on proper motions and their near-UV−V and V−K{sub s} colors. We present spectroscopic observations from the 2.4 m Hiltner Telescope at MDM Observatory. The new CV's orbital period is near 96 minutes, its spectrum shows the double-peaked Balmer emission lines characteristic of quiescent dwarf novae, and its V magnitude is near 18.2. Additionally, we present a full list of known CVs in the SUPERBLINK catalog.

  12. Hunting for eclipses: high-speed observations of cataclysmic variables

    Science.gov (United States)

    Hardy, L. K.; McAllister, M. J.; Dhillon, V. S.; Littlefair, S. P.; Bours, M. C. P.; Breedt, E.; Butterley, T.; Chakpor, A.; Irawati, P.; Kerry, P.; Marsh, T. R.; Parsons, S. G.; Savoury, C. D. J.; Wilson, R. W.; Woudt, P. A.

    2017-03-01

    We present new time-resolved photometry of 74 cataclysmic variables (CVs), 47 of which are eclipsing. Thirteen of these eclipsing systems are newly discovered. For all 47 eclipsing systems, we show high cadence (1-20 s) light curves obtained with the high-speed cameras ULTRACAM and ULTRASPEC. We provide new or refined ephemerides, and supply mid-eclipse times for all observed eclipses. We assess the potential for light-curve modelling of all 47 eclipsing systems to determine their system parameters, finding 20 systems that appear to be suitable for future study. Systems of particular interest include V713 Cep, in which we observed a temporary switching-off of accretion; and ASASSN-14mv and CSS111019:233313-155744, which both have orbital periods well below the CV period minimum. The short orbital periods and light-curve shapes suggest that they may be double degenerate (AM CVn) systems or CVs with evolved donor stars.

  13. Cataclysmic Variables in the SUPERBLINK Proper Motion Survey

    CERN Document Server

    Skinner, Julie N; Lépine, Sébastien

    2014-01-01

    We have discovered a new high proper motion cataclysmic variable (CV) in the SUPERBLINK proper motion survey, which is sensitive to stars with proper motions greater than 40 mas/yr. This CV was selected for follow-up observations as part of a larger search for CVs selected based on proper motions and their NUV-V and V-K$_{s}$ colors. We present spectroscopic observations from the 2.4m Hiltner Telescope at MDM Observatory. The new CV's orbital period is near 96 minutes, its spectrum shows the double-peaked Balmer emission lines characteristic of quiescent dwarf novae, and its V magnitude is near 18.2. Additionally, we present a full list of known CVs in the SUPERBLINK catalog.

  14. IGR J18293-1213 is an eclipsing Cataclysmic Variable

    CERN Document Server

    Clavel, Maïca; Bodaghee, A; Chiu, J -L; Fornasini, F M; Hong, J; Krivonos, R; Ponti, G; Rahoui, F; Stern, D

    2016-01-01

    Studying the population of faint hard X-ray sources along the plane of the Galaxy is challenging because of high-extinction and crowding, which make the identification of individual sources more difficult. IGR J18293-1213 is part of the population of persistent sources which have been discovered by the INTEGRAL satellite. We report on NuSTAR and Swift/XRT observations of this source, performed on 2015 September 11. We detected three eclipsing intervals in the NuSTAR light curve, allowing us to constrain the duration of these eclipses, $\\Delta t = 30.8^{+6.3}_{-0.0}$ min, and the orbital period of the system, $T = 6.92\\pm0.01$ hr. Even though we only report an upper limit on the amplitude of a putative spin modulation, the orbital period and the hard thermal Bremsstrahlung spectrum of IGR J18293-1213 provide strong evidence that this source is a magnetic Cataclysmic Variable (CV). Our NuSTAR and Swift/XRT joint spectral analysis places strong constraints on the white dwarf mass $M_{\\rm wd} = 0.78^{+0.10}_{-0.0...

  15. Photometry of some neglected bright cataclysmic variables and candidates

    CERN Document Server

    Bruch, Albert

    2016-01-01

    As part of an effort to better characterize bright cataclysmic variables (CVs) which have received little attention in the past light curves of four confirmed systems (CZ Aql, BO Cet, V380 Oph and EF Tuc) and one candidate (Lib 3) are analyzed. For none of these stars time resolved photometry has been published previously. While no variability was found in the case of Lib 3, which thus cannot be confirmed as a CV, the light curves of all other targets are dominated by strong flickering. Modulations on hourly time scales superimposed on the flickering can probably be related to orbital variations in BO Cet and V380 Oph, but not in CZ Aql and EF Tuc. Variations on the time scale of 10 minutes in CZ Aql, while not yet constituting convincing evidence, together with previous suspicions of a magnetically channeled accretion flow may point at an intermediate polar nature of this star. Some properties of the flickering are quantified in an effort to enlarge the data base for future comparative flickering studies in ...

  16. Two Cataclysmic Variables Identified from ROSAT Bright Sources

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This paper presents the results of optical spectroscopic observations of two ROSAT bright sources, 1RXS J020928.9+283243 and 1RXS J042332.8+745300. The low-dispersion spectra suggest the cataclysmic variable classification for the two objects. Further photometric observations are expected to reveal the variable features and to confirm the classifications.

  17. Studies of an x ray selected sample of cataclysmic variables. Ph.D. Thesis

    Science.gov (United States)

    Silber, Andrew D.

    1986-01-01

    Just prior to the thesis research, an all-sky survey in hard x rays with the HEAO-1 satellite and further observations in the optical resulted in a catalog of about 700 x-ray sources with known optical counterparts. This sample includes 43 cataclysmic variables, which are binaries consisting of a detached white-dwarf and a Roche lobe filling companion star. This thesis consists of studies of the x-ray selected sample of catalcysmic variables.

  18. Dynamical formation of cataclysmic variables in globular clusters

    Science.gov (United States)

    Hong, Jongsuk; Vesperini, Enrico; Belloni, Diogo; Giersz, Mirek

    2017-01-01

    The formation and evolution of X-ray sources in globular clusters is likely to be affected by the cluster internal dynamics and the stellar interactions in the cluster dense environment. Several observational studies have revealed a correlation between the number of X-ray sources and the stellar encounter rate, and provided evidence of the role of dynamics in the formation of X-ray binaries. We have performed a survey of Monte Carlo simulations aimed at exploring the connection between the dynamics and formation of cataclysmic variables (CVs) and the origin of the observed correlation between the number of these objects, Ncv, and the stellar encounter rate, Γ. The results of our simulations show a correlation between Ncv and Γ, as found in observational data, illustrate the essential role played by the dynamics, and shed light on the dynamical history behind this correlation. CVs in our simulations are more centrally concentrated than single stars with masses close to those of turn-off stars, although this trend is stronger for CVs formed from primordial binaries undergoing exchange encounters, which include a population of more massive CVs absent in the group of CVs formed from binaries not suffering any component exchange.

  19. On the late spectral types of cataclysmic variable secondaries

    CERN Document Server

    Baraffe, I

    2000-01-01

    We investigate why the spectral type of most cataclysmic variable (CV) secondaries is significantly later than that of a ZAMS star with the same mean density. Using improved stellar input physics, tested against observations of low-mass stars at the bottom of the main sequence, we calculate the secular evolution of CVs with low-mass donors. We consider sequences with different mass transfer rates and with a different degree of nuclear evolution of the donor prior to mass transfer. Systems near the upper edge of the gap ($P \\sim 3 - 6$ h) can be reproduced by models with a wide range of mass transfer rates from $1.5 \\times 10^{-9} \\msolyr$ to $10^{-8} \\msolyr$. Evolutionary sequences with a small transfer rate and donors that are substantially evolved off the ZAMS (central hydrogen content $0.05-0.5$) reproduce CVs with late spectral types above $P \\simgr$ 6 h. Systems with the most discrepant (late) spectral type should have the smallest donor mass at any given $P$. Consistency with the period gap suggests th...

  20. Excess mid-IR emission in Cataclysmic Variables

    CERN Document Server

    Dubus, G; Kern, B; Taam, R E; Spruit, H C

    2004-01-01

    We present a search for excess mid-IR emission due to circumbinary material in the orbital plane of cataclysmic variables (CVs). Our motivation stems from the fact that the strong braking exerted by a circumbinary (CB) disc on the binary system could explain several puzzles in our current understanding of CV evolution. Since theoretical estimates predict that the emission from a CB disc can dominate the spectral energy distribution (SED) of the system at wavelengths > 5 microns, we obtained simultaneous visible to mid-IR SEDs for eight systems. We report detections of SS Cyg at 11.7 microns and AE Aqr at 17.6 microns, both in excess of the contribution from the secondary star. In AE Aqr, the IR likely originates from synchrotron-emitting clouds propelled by the white dwarf. In SS Cyg, we argue that the observed mid-IR variability is difficult to reconcile with simple models of CB discs and we consider free-free emission from a wind. In the other systems, our mid-IR upper limits place strong constraints on the...

  1. Cataclysmic Variables below the Period Gap: Mass Determinations of 14 Eclipsing Systems

    CERN Document Server

    Savoury, C D J; Dhillon, V S; Marsh, T R; Gaensicke, B T; Copperwheat, C M; Kerry, P; Hickman, R D G; Parsons, S G

    2011-01-01

    We present high-speed, three-colour photometry of the eclipsing cataclysmic variables CTCV 1300, CTCV 2354 and SDSS 1152. All three systems are below the observed "period gap" for cataclysmic variables. For each system we determine the system parameters by fitting a parameterised model to the observed eclipse light curve by chi-squared minimisation. We also present an updated analysis of all other eclipsing systems previously analysed by our group. New donor masses are generally between 1 and 2 sigma of those originally published, with the exception of SDSS 1502 and DV UMa. We note that the donor mass of SDSS 1501 has been revised upwards by 0.024Msun. This system was previously identified as having evolved passed the minimum orbital period for cataclysmic variables, but the new mass determination suggests otherwise. Our new analysis confirms that SDSS 1035 and SDSS 1433 have evolved past the period minimum for cataclysmic variables, corroborating our earlier studies. We find that the radii of donor stars are...

  2. Observations of the Cataclysmic Variable 1 RXPJ113123+4322.5

    Science.gov (United States)

    Holtgrewe, Kirk S.; Durig, Douglas T.

    We observed the cataclysmic variable star l RXPJ113123+4322.5 while it was undergoing its recent outburst. We collected data using R and V filters, alternating the filters every two minutes. We obtained two to three hour-long data sets on two different nights. The light curve was analyzed using Mathematica. The period determined was near 95 minutes and there was also some indication of a lower amplitude, higher frequency variation.

  3. Angular momentum transport in the magnetospheres of cataclysmic variable accretion discs

    Energy Technology Data Exchange (ETDEWEB)

    Koen, C.

    1986-12-01

    The theory of stellar magnetic braking is applied to circumstellar discs. The focus is concentrated on cataclysmic variable stars but results apply to any disc in which the rotational velocity is Keplerian. Calculations are done for two magnetic field configurations and numerical results given for a range of physical parameter values. It is found that magnetic processes could be efficient in the removal of angular momentum from such systems.

  4. Detached cataclysmic variables are crossing the orbital period gap

    CERN Document Server

    Zorotovic, Monica; Parsons, Steven G; Gänsicke, Boris T; Hardy, Adam; Agurto-Gangas, Carolina; Gómez-Morán, Ada Nebot; Rebassa-Mansergas, Alberto; Schwope, Axel D

    2016-01-01

    A central hypothesis in the theory of cataclysmic variable (CV) evolution is the need to explain the observed lack of accreting systems in the ~2-3 h orbital period range, known as the period gap. The standard model, disrupted magnetic braking (DMB), reproduces the gap by postulating that CVs transform into inconspicuous detached white dwarf (WD) plus main sequence (MS) systems, which no longer resemble CVs. However, observational evidence for this standard model is currently indirect and thus this scenario has attracted some criticism throughout the last decades. Here we perform a simple but exceptionally strong test of the existence of detached CVs (dCVs). If the theory is correct dCVs should produce a peak in the orbital period distribution of detached close binaries consisting of a WD and an M4-M6 secondary star. We measured six new periods which brings the sample of such binaries with known periods below 10 h to 52 systems. An increase of systems in the ~2-3 h orbital period range is observed. Comparing ...

  5. Dynamical Formation of Cataclysmic Variables in Globular Clusters

    CERN Document Server

    Hong, Jongsuk; Belloni, Diogo; Giersz, Mirek

    2016-01-01

    The formation and evolution of X-ray sources in globular clusters is likely to be affected by the cluster internal dynamics and the stellar interactions in the cluster dense environment.Several observational studies have revealed a correlation between the number of X-ray sources and the stellar encounter rate and provided evidence of the role of dynamics in the formation of X-ray binaries. We have performed a survey of Monte-Carlo simulations aimed at exploring the connection between the dynamics and formation of cataclysmic variables (CVs) and the origin of the observed correlation between the number of these objects, $N_{\\rm cv}$, and the stellar encounter rate, $\\Gamma$.The results of our simulations show a correlation between $N_{\\rm cv}$ and $\\Gamma$ as found in observational data, illustrate the essential role played by dynamics, and shed light on the dynamical history behind this correlation. CVs in our simulations are more centrally concentrated than single stars with masses close to those of turn-off...

  6. AE Aquarii represents a new subclass of Cataclysmic Variables

    CERN Document Server

    Ikhsanov, N R

    2012-01-01

    We analyze properties of the unique nova-like star AE Aquarii identified with a close binary system containing a red dwarf and a very fast rotating magnetized white dwarf. It cannot be assigned to any of the three commonly adopted sub-classes of Cataclysmic Variables: Polars, Intermediate Polars, and Accreting non-magnetized White Dwarfs. Our study has shown that the white dwarf in AE Aqr is in the ejector state and its dipole magnetic moment is $\\mu ~ 1.5 \\times 10^{34} G cm^3$. It switched into this state due to intensive mass exchange between the system components during a previous epoch. A high rate of disk accretion onto the white dwarf surface resulted in temporary screening of its magnetic field and spin-up of the white dwarf to its present spin period. Transition of the white dwarf to the ejector state had occurred at a final stage of the spin-up epoch as its magnetic field emerged from the accreted plasma due to diffusion. In the frame of this scenario AE Aqr represents a missing link in the chain of...

  7. Sky surveys of interest for cataclysmic variables

    Science.gov (United States)

    Szkody, Paula

    2016-07-01

    Sky Surveys provide much useful information for finding and understanding catacylsmic variables (CVs). Depending on the length of time the survey runs and the cadence used, the surveys can easily locate novae and dwarf novae based on the amplitude and shape of the light curves. For systems with high inclination or prominent hot spots and periods of hours, some orbital information can be derived from eclipses that are caught or repetitive modulations in the folded light curves. However, in most cases, detailed knowledge of the type of system and its orbital period must come from extended observations at other wavelengths, as most surveys take place in one filter or unfiltered. Currently, we are in the midst of an explosion of recently past, continuing and future plans for sky surveys. The Sloan Digital Sky Survey found about 300 CVs in its Legacy Mode, with small numbers continuing to be added through the extended phases. The CVs were primarily identified through spectroscopic coverage of selected objects from the photometric survey and subsequently found a wide variety of systems (polars, intermediate polars, novalikes, dwarf novae, objects with pulsating white dwarfs) due to spectroscopic differences among these types. The Palomar Transit Factory (PTF), Intermediate PTF and future Zwicky Transient Facilty (ZTF) operate in the same mode of candidate discovery via outbursts followed by spectroscopy for confirmation. The Catalina Real-Time Transient Survey primarily adds dwarf novae that are found from outbursts in the long time span of observations. The Kepler K2 mission operates with a much higher cadence (48-1440 observations/day) but shorter total length (70-80 days) and thus finds CVs through orbital variability as well as those with short outburst intervals. Gaia will provide distances for most of the objects under study, thus locating them in the galaxy. The upcoming Large Synoptic Survey Telescope (LSST) will go much fainter and cover variability on a 10 yr

  8. Searching for Cataclysmic Variables in the J-PLUS Survey

    Science.gov (United States)

    Abril, J.; Ederoclite, A.

    2017-03-01

    Cataclysmic Variables (CVs) are binary systems made of a white dwarf which is accreting mass from a less evolved companion. Depending on the physical properties of the system, the observational characteristics of CVs can be very diverse. Nevertheless, as we learned from projects like the Sloan Digital Sky Survey, CVs occupy the same locus of quasars in color- color diagrams, hence their discovery can be quite challenging. In this paper, we expose how the filter set of the J-PLUS project can help to efficiently separate CVs from other objects (mostly quasars) and even get their type. Through simulations and real data, we explain how accurate the method is and identify the following steps to finally get the first complete unbiased magnitude-limited sample of Cataclysmic Variables to date, a fundamental data set to be able to study the evolution of this type of objects.

  9. Cataclysmic variables in Globular clusters: First results on the analysis of the MOCCA simulations database

    CERN Document Server

    Belloni, Diogo; Askar, Abbas; Hypki, Arkadiusz

    2016-01-01

    In this first investigation of the MOCCA database with respect to cataclysmic variables, we found that for models with Kroupa initial distributions, considering the standard value of the efficiency of the common-envelope phase adopted in BSE, no single cataclysmic variable was formed only via binary stellar evolution, i. e., in order to form them, strong dynamical interactions have to take place. Our results also indicate that the population of cataclysmic variables in globular clusters are, mainly, in the last stage of their evolution and observational selection effects can change drastically the expected number and properties of observed cataclysmic variables.

  10. Hunting For Eclipses: High Speed Observations of Cataclysmic Variables

    CERN Document Server

    Hardy, Liam K; Dhillon, Vik S; Littlefair, Stuart P; Bours, Madelon C P; Breedt, Elme; Butterley, Tim; Chakpor, Anurak; Irawati, Puji; Kerry, Paul; Marsh, Tom R; Parsons, Steven G; Savoury, Chris D J; Wilson, Richard W; Woudt, Patrick A

    2016-01-01

    We present new time-resolved photometry of 74 cataclysmic variables (CVs), 47 of which are eclipsing. 13 of these eclipsing systems are newly discovered. For all 47 eclipsing systems we show high cadence (1-20 seconds) light curves obtained with the high-speed cameras ultracam and ultraspec. We provide new or refined ephemerides, and supply mid-eclipse times for all observed eclipses. We assess the potential for light curve modelling of all 47 eclipsing systems to determine their system parameters, finding 20 systems which appear to be suitable for future study.

  11. Followup Observations of SDSS and CRTS Candidate Cataclysmic Variables

    OpenAIRE

    Szkody, Paula; Everett, Mark E.; Howell, Steve B.; Landolt, Arlo U.; Bond, Howard E.; Silva, David R.; Vasquez-Soltero, Stephanie

    2014-01-01

    We present photometry of 11 and spectroscopy of 35 potential cataclysmic variables from the Sloan Digital Sky Survey, the Catalina Real-Time Transient Survey and vsnet-alerts. The photometry results include quasi-periodic oscillations during the decline of V1363 Cyg, nightly accretion changes in the likely Polar (AM Herculis binary) SDSS J1344+20, eclipses in SDSS J2141+05 with an orbital period of 76+/-2 min, and possible eclipses in SDSS J2158+09 at an orbital period near 100 min. Time-reso...

  12. The Magnetic Cataclysmic Variable LSQ1725-64

    CERN Document Server

    Fuchs, J T; Dennihy, E; O'Donoghue, D; Clemens, J C; Reichart, D E; Moore, J P; LaCluyze, A P; Haislip, J B; Ivarsen, K V

    2016-01-01

    We present new photometry and spectroscopy of the 94m eclipsing binary LSQ1725-64 that provide insight into the fundamental parameters and evolutionary state of this system. We confirm that LSQ1725-64 is a magnetic cataclysmic variable whose white dwarf has a surface-averaged magnetic field strength of $12.5 \\pm 0.5$ MG measured from Zeeman splitting. The spectral type and colour of the secondary, as well as the eclipse length, are consistent with other secondaries that have not yet evolved through the period minimum expected for cataclysmic variables. We observe two different states of mass transfer and measure the transition between the two to occur over about 45 orbital cycles. In the low state, we observe photometric variations that we hypothesize to arise predominantly from two previously heated magnetic poles of the white dwarf. Our precise eclipse measurements allow us to determine binary parameters of LSQ1725-64 and we find it contains a high mass ($0.97 \\pm 0.03\\ M_{\\odot}$) white dwarf if we assume ...

  13. The Formation of Cataclysmic Variables: The Influence of Nova Eruptions

    Science.gov (United States)

    Nelemans, G.; Siess, L.; Repetto, S.; Toonen, S.; Phinney, E. S.

    2016-01-01

    The theoretical and observed populations of pre-cataclysmic variables are dominated by systems with low-mass white dwarfs (WDs), while the WD masses in cataclysmic variables (CVs) are typically high. In addition, the space density of CVs is found to be significantly lower than in the theoretical models. We investigate the influence of nova outbursts on the formation and initial evolution of CVs. In particular, we calculate the stability of the mass transfer in the case where all of the material accreted on the WD is lost in classical novae and part of the energy to eject the material comes from a common-envelope-like interaction with the companion. In addition, we study the effect of an asymmetry in the mass ejection that may lead to small eccentricities in the orbit. We find that a common-envelope-like ejection significantly decreases the stability of the mass transfer, particularly for low-mass WDs. Similarly, the influence of asymmetric mass loss can be important for short-period systems and even more so for low-mass WDs; however, this influence likely disappears long before the next nova outburst due to orbital circularization. In both cases the mass-transfer rates increase, which may lead to observable (and perhaps already observed) consequences for systems that do survive to become CVs. However, a more detailed investigation of the interaction between nova ejecta and the companion and the evolution of slightly eccentric CVs is needed before definite conclusions can be drawn.

  14. Cataclysmic Variables from SDSS II. The Second Year

    CERN Document Server

    Szkody, P; Silvestri, N M; Henden, A A; Anderson, S F; Frith, W J; Lawton, B; Owens, E; Raymond, S; Schmidt, G; Wolfe, M; Bochanski, J J; Covey, K; Harris, H; Hawley, S; Knapp, G R; Margon, B; Voges, W; Walkowicz, L; Brinkmann, J; Lamb, D Q; Anderson, Scott F.; Bochanski, John; Covey, Kevin; Fraser, Oliver; Frith, James; Harris, Hugh; Hawley, Suzanne; Henden, Arne; Knapp, Gillian R.; Lawton, Brandon; Margon, Bruce; Owens, Ethan; Raymond, Sean; Schmidt, Gary; Silvestri, Nicole; Szkody, Paula; Voges, Wolfgang; Walkowicz, Lucianne; Wolfe, Michael

    2003-01-01

    The first full year of operation following the commissioning year of the Sloan Digital Sky Survey has revealed a wide variety of newly discovered cataclysmic variables. We show the SDSS spectra of forty-two cataclysmic variables observed in 2002, of which thirty-five are new classifications, four are known dwarf novae (CT Hya, RZ Leo, T Leo and BZ UMa), one is a known CV identified from a previous quasar survey (Aqr1) and two are known ROSAT or FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS positions, colors and spectra of all forty-two systems are presented. In addition, the results of follow-up studies of several of these objects identify the orbital periods, velocity curves and polarization that provide the system geometry and accretion properties. While most of the SDSS discovered systems are faint (>18th mag) with low accretion rates (as implied from their spectral characteristics), there are also a few bright objects which may have escaped previous surveys due to changes in the ...

  15. Rapid Oscillations in Cataclysmic Variables. XV. HT Camelopardalis (= RX J0757.0+6306)

    CERN Document Server

    Kemp, J; Thorstensen, J R; Fried, R E; Skillman, D R; Billings, G W; Kemp, Jonathan; Patterson, Joseph; Thorstensen, John; Fried, Robert; Skillman, David; Billings, Gary

    2002-01-01

    We present photometry and spectroscopy of HT Camelopardalis, a recently discovered X-ray-bright cataclysmic variable. The spectrum shows bright lines of H, He I, and He II, all moving with a period of 0.059712(1) d, which we interpret as the orbital period. The star's brightness varies with a strict period of 515.0592(2) s, and a mean full amplitude of 0.11 mag. These properties qualify it as a /bona fide/ DQ Herculis star (intermediate polar) -- in which the magnetism of the rapidly rotating white dwarf channels accretion flow to the surface. Normally at V=17.8, the star shows rare and very brief outbursts to V=12-13. We observed one in December 2001, and found that the 515 s pulse amplitude had increased by a factor of ~100 (in flux units). A transient orbital signal may also have appeared.

  16. On the White Dwarf Mass Problem of Cataclysmic Variables

    CERN Document Server

    Liu, Wei-Min

    2016-01-01

    Recent observations show that the white dwarfs (WDs) in cataclysmic Variables (CVs) have an average mass significantly higher than isolated WDs and WDs in post-common envelope binaries (PCEBs), which are thought to the progenitors of CVs. This suggests that either the WDs have grown in mass during the PCEB/CV evolution or the binaries with low-mass WDs are unable to evolve to be CVs. In this paper, we calculate the evolution of accreting WD binaries with updated hydrogen accumulation efficiency and angular momentum loss prescriptions. We show that thermal timescale mass transfer is not effective in changing the average WD mass distribution. The WD mass discrepancy is most likely related to unstable mass transfer in WD binaries in which an efficient mechanism of angular momentum loss is required.

  17. 2MASSJ22560844+5954299: the newly discovered cataclysmic star with the deepest eclipse

    CERN Document Server

    Kjurkchieva, D; Dimitrov, D; Groebel, R; Ibryamov, S; Nikolov, G

    2015-01-01

    Context: The SW Sex stars are assumed to represent a distinguished stage in CV evolution, making it especially important to study them. Aims: We discovered a new cataclysmic star and carried out prolonged and precise photometric observations, as well as medium-resolution spectral observations. Modelling these data allowed us to determine the psysical parameters and to establish its peculiarities. Results: The newly discovered vataclysmic variable 2MASSJ22560844+5954299 shows the deepest eclipse amongst the known nova-like stars. It was reproduced by totally covering a very luminous accretion disk by a red secondary component. The temperature distribution of the disk is flatter than that of steady-state disk. The target is unusual with the combination of a low mass ratio q~1.0 (considerably below the limit q=1.2 of stable mass transfer of CVs) and an M-star secondary. The intensity of the observed three emission lines, H_alpha, He 5875, and He 6678, sharply increases around phase 0.0, accompanied by a Doppler ...

  18. Orbital periods of cataclysmic variables identified by the SDSS. VII. Four new eclipsing systems

    CERN Document Server

    Southworth, John; Gansicke, B T; Pyrzas, S

    2009-01-01

    We present photometry of nine cataclysmic variable stars identified by the Sloan Digital Sky Survey, aimed at measuring the orbital periods of these systems. Four of these objects show deep eclipses, from which we measure their orbital periods. The light curves of three of the eclipsing systems are also analysed using the LCURVE code, and their mass ratios and orbital inclinations determined. SDSS J075059.97+141150.1 has an orbital period of 134.1564 +/- 0.0008 min, making it a useful object with which to investigate the evolutionary processes of cataclysmic variables. SDSS J092444.48+080150.9 has a period of 131.2432 +/- 0.0014 min and is probably magnetic. The white dwarf ingress and egress phases are very deep and short, and there is no clear evidence that this object has an accretion disc. SDSS J115207.00+404947.8 and SDSS J152419.33+220920.1 are nearly identical twins, with periods of 97.5 +/- 0.4 and 93.6 +/- 0.5 min and mass ratios of 0.14 +/- 0.03 and 0.17 +/- 0.03, respectively. Their eclipses have w...

  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. SPECTROSCOPIC ORBITAL PERIODS FOR 29 CATACLYSMIC VARIABLES FROM THE SLOAN DIGITAL SKY SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Thorstensen, John R.; Taylor, Cynthia J.; Peters, Christopher S.; Skinner, Julie N. [Department of Physics and Astronomy 6127 Wilder Laboratory, Dartmouth College Hanover, NH 03755-3528 (United States); Southworth, John [Astrophysics Group Keele University Staffordshire ST5 5BG (United Kingdom); Gänsicke, Boris T. [Department of Physics University of Warwick Coventry CV4 7AL (United Kingdom)

    2015-04-15

    We report follow-up spectroscopy of 29 cataclysmic variables from the Sloan Digital Sky Survey (SDSS), 22 of which were discovered by SDSS and seven of which are previously known systems that were recovered in SDSS. The periods for 16 of these objects were included in the tabulation by Gänsicke et al. While most of the systems have periods less than 2 hr, only one has a period in the 80–86 minutes “spike” found by Gänsicke et al., and 11 have periods longer than 3 hr, indicating that the present sample is skewed toward longer-period, higher-luminosity objects. Seven of the objects have spectra resembling dwarf novae, but have apparently never been observed in outburst, suggesting that many cataclysmics with relatively low variability amplitude remain to be discovered. Some of the objects are notable. SDSS J07568+0858 and SDSS J08129+1911 were previously known to have deep eclipses; in addition to spectroscopy, we use archival data from the Catalina Real Time Transient Survey to refine their periods. We give a parallax-based distance of 195 (+54, −39) pc for LV Cnc (SDSS J09197+0857), which at P{sub orb} = 81 m has the shortest orbital period in our sample. SDSS J08091+3814 shows both the spectroscopic phase offset and phase-dependent absorption found in SW Sextantis stars. The average spectra of SDSS J08055+0720 and SDSS J16191+1351 show contributions from K-type secondaries, and SDSS J080440+0239 shows a contribution from an early M star. We use these to constrain the distances. SDSS J09459+2922 has characteristics typical of a magnetic system. SDSS11324+6249 may be a novalike variable, and if so, its orbital period (99 minutes) is unusually short for that subclass.

  1. Interferometric Astrometry with Hubble Space Telescope Fine Guidance Sensor 3 The Parallax of the Cataclysmic Variable TV Columbae

    CERN Document Server

    McArthur, B E; Lee, J; Van Altena, W F; Slesnick, C L; Rhee, J T; Patterson, R J; Fredrick, L W; Spiesman, W J; Nelan, E; Duncombe, R L; Hemenway, P D; Jefferys, W H; Shelus, P J; Franz, O G; Wasserman, L H

    2001-01-01

    TV Columbae (TV Col) is a 13th magnitude Intermediate Polar (IP) Cataclysmic Variable (CV), with multiple periods found in the light curves. Past estimates predicted a distance of 400 parsec to greater than 500 parsec. Recently completed Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) interferometric observations allow us to determine the first trigonometric parallax to TV Col. This determination puts the distance of TV Col at 368 -15+17 parsecs. CD-32 2376, a 10th magnitude Tycho Catalog star, is a reference star in the TV Col frame. We find a distance of $127.7 -1+1 parsecs.

  2. A spectroscopic search for faint secondaries in cataclysmic variables

    CERN Document Server

    Putte, D V; Hawkins, N A; Martin, J S; Smith, Robert Connon

    2003-01-01

    The secondary in cataclysmic variables (CV's) is usually detected by cross-correlation of the CV spectrum with that of a K or M dwarf template, to produce a radial velocity curve. Although this method has demonstrated its power, it has its limits in the case of noisy spectra, such as are found when the secondary is faint. A method of co-adding spectra, called skew mapping, has been proposed in the past. Gradually, examples of its application are being published. Nonetheless, so far no journal article has described the technique in detail. To answer this need, this paper explores in detail the capabilities of skew mapping when determining the amplitude of the radial velocity for faint secondaries. It demonstrates the method's power over techniques that are more conventional, when the signal-to-noise (s/n) ratio is poor. The paper suggests an approach to assessing the quality of results. This leads in the case of the investigated objects to a first tier of results, where we find K2=127+-23 km/s for SY Cnc, K2=1...

  3. A possible giant planet orbiting the cataclysmic variable LX Ser

    Science.gov (United States)

    Li, Kai; Hu, Shaoming; Zhou, Jilin; Wu, Donghong; Guo, Difu; Jiang, Yunguo; Gao, Dongyang; Chen, Xu; Wang, Xianyu

    2017-02-01

    LX Ser is a deeply eclipsing cataclysmic variable with an orbital period of 0.1584325 d. 62 new eclipse times were determined by our observations and the AAVSO International Data base. Combining all available eclipse times, we analyzed the O - C behavior of LX Ser. We found that the O - C diagram of LX Ser shows a sinusoidal oscillation with a period of 22.8 yr and an amplitude of 0.00035 d. Two mechanisms (i.e., the Applegate mechanism and the light-travel time effect) are applied to explain the cyclic modulation. We found that it is difficult to apply the Applegate mechanism to explain the cyclic oscillation in the orbital period. Therefore, the cyclic period change is most likely to be caused by the light-travel time effect due to the presence of a third body. The mass of the tertiary component was determined to be M3 ∼ 7.5 MJup. We supposed that the tertiary companion is plausibly a giant planet. The stability of the giant planet was checked, and we found that the multiple system is stable.

  4. The formation of Cataclysmic Variables: the influence of nova eruptions

    CERN Document Server

    Nelemans, G; Repetto, S; Toonen, S; Phinney, E S

    2015-01-01

    The theoretical and observed populations of pre-cataclysmic variables (pre-CVs) are dominated by systems with low-mass white dwarfs (WDs), while the WD masses in CVs are typically high. In addition, the space density of CVs is found to be significantly lower than theoretical models. We investigate the influence of nova outbursts on the formation and (initial) evolution of CVs. In particular, we calculate the stability of the mass transfer in case all the material accreted on the WD is lost in classical novae, and part of the energy to eject the material comes from a common-envelope like interaction with the companion. In addition, we study the effect of an asymmetry in the mass ejection, that may lead to small eccentricities in the orbit. We find that a common-envelope like ejection significantly decreases the stability of the mass transfer, in particular for low-mass WD. Similarly, the influence of asymmetric mass loss can be important for short-period systems and even more so for low-mass WD, but likely dis...

  5. A possible giant planet orbiting the cataclysmic variable LX Ser

    CERN Document Server

    Li, K; Zhou, J -L; Wu, D -H; Guo, D -F; Jiang, Y -G; Gao, D -Y; Chen, X; Wang, X -Y

    2016-01-01

    LX Ser is a deeply eclipsing cataclysmic variable with an orbital period of $0.^d 1584325$. Sixty two new eclipse times were determined by our observations and the AAVSO International Data base. Combining all available eclipse times, we analyzed the O-C behavior of LX Ser. We found that the O-C diagram of LX Ser shows a sinusoidal oscillation with a period of 22.8 yr and an amplitude of 0.00035 days. Two mechanisms (i.e., the Applegate mechanism and the light travel time effect) are applied to explain the cyclic modulation. We found that the Applegate mechanism is difficult to explain the cyclic oscillation in the orbital period. Therefore, the cyclic period change is most likely to be caused by the light travel time effect due to the presence of a third body. The mass of the tertiary component was determined to be $M_3\\sim7.5 M_{Jup}$. We supposed that the tertiary companion is plausible a giant planet. The stability of the giant planet was checked, and we found that the multiple system is stable.

  6. ULTRACAM photometry of the eclipsing cataclysmic variable OU Vir

    CERN Document Server

    Feline, W J; Marsh, T R; Stevenson, M J; Watson, C A; Brinkworth, C S

    2004-01-01

    We present high-speed, three-colour photometry of the faint eclipsing cataclysmic variable OU Vir. For the first time in OU Vir, separate eclipses of the white dwarf and bright spot have been observed. We use timings of these eclipses to derive a purely photometric model of the system, obtaining a mass ratio of q = 0.175 +/- 0.025, an inclination of i = 79.2 +/- 0.7 degrees and a disc radius of Rd/a = 0.2315 +/- 0.0150. We separate the white dwarf eclipse from the lightcurve and, by fitting a blackbody spectrum to its flux in each passband, obtain a white dwarf temperature of T = 13900 +/- 600 K and a distance of D = 51 +/- 17 pc. Assuming that the primary obeys the Nauenberg (1972) mass-radius relation for white dwarfs and allowing for temperature effects, we also find a primary mass Mw/Msun = 0.89 +/- 0.20, primary radius Rw/Rsun = 0.0097 +/- 0.0031 and orbital separation a/Rsun = 0.74 +/- 0.05.

  7. Exploring inside-out Doppler tomography: magnetic cataclysmic variables

    CERN Document Server

    Kotze, Enrico J; McBride, Vanessa A

    2016-01-01

    We present the results of applying our inside-out velocity projection and flux modulation mapping techniques to the Doppler tomography of magnetic cataclysmic variables. The inside-out tomogram is constructed by directly projecting phase-resolved spectra onto the inside-out framework. In addition, our flux modulation mapping technique extracts any information related to the modulation of the line flux by utilising consecutive half-phase tomograms. We apply this to both the standard and the inside-out techniques. Our test cases, the polars HU Aqr and V834 Cen, and the intermediate polar PQ Gem, were chosen because of their known accretion characteristics, namely ballistic, magnetic and curtain dominated accretion, respectively. In all three cases the inside-out tomogram better exposes low-velocity emission details which are overly compacted in the standard tomogram. This is especially apparent for the mid-inclination V834 Cen where the almost blob-like blended lower velocity emission in the standard tomogram i...

  8. Characterization of new hard X-ray Cataclysmic Variables

    CERN Document Server

    Bernardini, F; Falanga, M; Mukai, K; Matt, G; Bonnet-Bidaud, J -M; Masetti, N; Mouchet, M

    2012-01-01

    We aim at characterizing a sample of 9 new hard X-ray selected Cataclysmic Variable (CVs), to unambiguously identify them as magnetic systems of the Intermediate Polar (IP) type. We performed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM-Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Strong X-ray pulses at the White Dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGR J08390-4833, IGR J18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 posses a soft X-ray optica...

  9. New Southern Cataclysmic Variables: Discoveries from MASTER-SAAO

    Science.gov (United States)

    Buckley, D. A. H.; Potter, S. B.; Kniazev, A.; Lipunov, V.; Gorbovskoy, E.; Tiurina, N.

    2017-03-01

    In this paper we report on new cataclysmic variables (CVs) discovered by the first local optical transient detection system established at the SAAO Sutherland station, namely MASTER-SAAO. The characteristics of the MASTER-SAAO system are described and the parameters of the survey compared to the Catalina Real Time Survey (CRTS). To date MASTER-SAAO has discovered over 200 (non-Solar System) optical transients with about 75% of these being likely new CVs, most being dwarf novae (DNe). Approximately 50% of the DNe have outburst amplitudes in excess of 4 magnitudes, with some extreme amplitude (> 7 mag), probable WZ Sge systems. The MASTER-SAAO detection limit of B = 19–20 is comparable to the ˜20 magnitude limit of the CRTS (depending on CV colour). Based on the CV detection statistics of CRTS, we believe that MASTER-SAAO is detecting essentially the same CV population as CRTS, for a detection outburst amplitude threshold >2.2 magnitudes. We also present results of the initial follow-up program on CVs discovered by MASTER, including dwarf novae, a bright new VY Scl system and a new eclipsing polar.

  10. Nova-like cataclysmic variables in the infrared

    Energy Technology Data Exchange (ETDEWEB)

    Hoard, D. W. [Eureka Scientific, Inc., Oakland, CA (United States); Long, Knox S. [Space Telescope Science Institute, Baltimore, MD (United States); Howell, Steve B. [NASA Ames Research Center, Moffett Field, CA (United States); Wachter, Stefanie [Max Planck Institut für Astronomie, D-69117 Heidelberg (Germany); Brinkworth, Carolyn S. [Spitzer Science Center, California Institute of Technology, Pasadena, CA (United States); Knigge, Christian [Physics and Astronomy, University of Southampton, Southampton (United Kingdom); Drew, J. E. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield (United Kingdom); Szkody, Paula [Department of Astronomy, University of Washington, Seattle, WA (United States); Kafka, S. [Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC (United States); Belle, Kunegunda [Los Alamos National Laboratory, Los Alamos, NM (United States); Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA (United States); Froning, Cynthia S. [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO (United States); Van Belle, Gerard T. [Lowell Observatory, Flagstaff, AZ (United States); Pretorius, M. L., E-mail: hoard@mpia.de [Department of Physics, University of Oxford, Oxford (United Kingdom)

    2014-05-01

    Nova-like (NL) cataclysmic variables have persistently high mass transfer rates and prominent steady state accretion disks. We present an analysis of infrared observations of 12 NLs obtained from the Two Micron All Sky Survey, the Spitzer Space Telescope, and the Wide-field Infrared Survey Explorer All Sky Survey. The presence of an infrared excess at λ ≳ 3-5 μm over the expectation of a theoretical steady state accretion disk is ubiquitous in our sample. The strength of the infrared excess is not correlated with orbital period, but shows a statistically significant correlation (but shallow trend) with system inclination that might be partially (but not completely) linked to the increasing view of the cooler outer accretion disk and disk rim at higher inclinations. We discuss the possible origin of the infrared excess in terms of emission from bremsstrahlung or circumbinary dust, with either mechanism facilitated by the mass outflows (e.g., disk wind/corona, accretion stream overflow, and so on) present in NLs. Our comparison of the relative advantages and disadvantages of either mechanism for explaining the observations suggests that the situation is rather ambiguous, largely circumstantial, and in need of stricter observational constraints.

  11. On the diversity and similarity of outbursts of symbiotic binaries and cataclysmic variables

    CERN Document Server

    Skopal, Augustin

    2015-01-01

    Outbursts in two classes of interacting binary systems, the symbiotic stars (SSs) and the cataclysmic variables (CVs), show a number of similarities in spite of very different orbital periods. Typical values for SSs are in the order of years, whereas for CVs they are of a few hours. Both systems undergo unpredictable outbursts, characterized by a brightening in the optical by 1 - 3 and 7 - 15 mag for SSs and CVs, respectively. By modelling the multiwavelength SED of selected examples from both groups of these interacting binaries, I determine their basic physical parameters at a given time of the outburst evolution. In this way I show that the principal difference between outbursts of these objects is their violence, whereas the ionization structure of their ejecta is basically very similar. This suggests that the mechanism of the mass ejection by the white dwarfs in these systems is also similar.

  12. Investigations of a new eclipsing cataclysmic variable HBHA 4705-03

    CERN Document Server

    Yakin, D G; Shimansky, V V; Vlasyuk, V V; Spiridonova, O I

    2012-01-01

    Results of photometric and spectroscopic investigations of the recently discovered eclipsing cataclysmic variable star HBHA 4705-03 are presented. The emission spectra of the system show broad hydrogen and helium emission lines. The bright spots with an approximately zero velocity components are found in the Doppler maps for the hydrogen and ionized helium lines. The disc structure is more prominent in the maps for the neutral helium lines. The masses of the components (M_WD = 0.54 \\pm 0.10 M_sun and M_RD = 0.45 \\pm 0.05 M_sun), and the orbit inclination (i = 71.8 \\pm 0.^7 deg) were estimated using the radial velocity light curve and the eclipse width. The modeling of the light curve allows us to evaluate the bright spot parameters and the mass accretion rate (\\dot M \\approx 2 10^{17} g s^{-1}).

  13. BK Lyncis: The Oldest Old Nova?... And a Bellwether for Cataclysmic-Variable Evolution

    CERN Document Server

    Patterson, Joseph; Kemp, Jonathan; de Miguel, Enrique; Krajci, Thomas; Foote, Jerry; Hambsch, Franz-Josef; Campbell, Tut; Roberts, George; Cejudo, David; Dvorak, Shawn; Vanmunster, Tonny; Koff, Robert; Skillman, David; Harvey, David; Martin, Brian; Rock, John; Boyd, David; Oksanen, Arto; Morelle, Etienne; Ulowetz, Joseph; Kroes, Anthony; Sabo, Richard; Jensen, Lasse

    2012-01-01

    We summarize the results of a 20-year campaign to study the light curves of BK Lyncis, a nova-like star strangely located below the 2-3 hour orbital period gap in the family of cataclysmic variables. Two apparent "superhumps" dominate the nightly light curves - with periods 4.6% longer, and 3.0% shorter, than P_orb. The first appears to be associated with the star's brighter states (V~14), while the second appears to be present throughout and becomes very dominant in the low state (V~15.7). Starting in the year 2005, the star's light curve became indistinguishable from that of a dwarf nova - in particular, that of the ER UMa subclass. Reviewing all the star's oddities, we speculate: (a) BK Lyn is the remnant of the probable nova on 30 December 101, and (b) it has been fading ever since, but has taken ~2000 years for the accretion rate to drop sufficiently to permit dwarf-nova eruptions. If such behavior is common, it can explain other puzzles of CV evolution. One: why the ER UMa class even exists (because all...

  14. Variable stars with the Kepler space telescope

    CERN Document Server

    Molnár, László; Plachy, Emese

    2016-01-01

    The Kepler space telescope has revolutionised our knowledge about exoplanets and stars and is continuing to do so in the K2 mission. The exquisite photometric precision, together with the long, uninterrupted observations opened up a new way to investigate the structure and evolution of stars. Asteroseismology, the study of stellar oscillations, allowed us to investigate solar-like stars and to peer into the insides of red giants and massive stars. But many discoveries have been made about classical variable stars too, ranging from pulsators like Cepheids and RR Lyraes to eclipsing binary stars and cataclysmic variables, and even supernovae. In this review, which is far from an exhaustive summary of all results obtained with Kepler, we collected some of the most interesting discoveries, and ponder on the role for amateur observers in this golden era of stellar astrophysics.

  15. Cataclysmic Variables and a Candidate Helium White Dwarf in the Globular Cluster NGC 6397

    CERN Document Server

    Edmonds, P D; Cool, A M; Cohn, H N; Lugger, P M; Bailyn, C D; Edmonds, Peter D.; Grindlay, Jonathan E.; Cool, Adrienne M.; Cohn, Haldan N.; Lugger, Phyllis N.; Bailyn, Charles D.

    1999-01-01

    We have used HST/FOS to study faint UV stars in the core of the nearby globular cluster NGC 6397. We confirm the presence of a 4th cataclysmic variable (CV) in NGC 6397 (CV 4), and we use the photometry of Cool et al. (1998) to present evidence that CVs 1--4 all have faint disks and probably low accretion rates. By combining these results with new UV spectra of CV 1 and the published spectra of Grindlay et al. (1995) we present new evidence that CVs 1--3 may be DQ Her systems, and we show that CV 4 may either be a dwarf nova or another magnetic system. Another possibility is that the CVs could be old novae in hibernation between nova eruptions. We also present the first spectrum of a member of a new class of UV bright stars in NGC 6397. These faint, hot stars do not vary, unlike the CVs, and are thus denoted as ``non-flickerers'' (NFs). Like the CVs, their spatial concentration is strongly concentrated toward the cluster center. Using stellar atmosphere models we have determined log g = 6.25, and T_eff = 17,5...

  16. Short-period cataclysmic variables at Observatorio Astronomico Nacional IA UNAM.

    Science.gov (United States)

    Zharikov, S.

    2014-03-01

    We present results of time-resolved spectroscopy and photometry of faint (∼17-19 mag) Cataclysmic Variable stars with periods around the minimum orbital period (∼80 min). In this work we concentrated to our results of study of CVs systems which have evolved beyond the period minimum (so-called bounce-back systems). Using various instruments attached to 2.1m, 1.5m and 0.84m telescopes of OAN SPM of IA UNAM we explored conditions and structure of accretion disks in those short-period Cataclysmic Variables. We showed that the accretion disk in a system with an extremely low mass ratio (≤0.05) grows in the size reaching 2:1 resonance radius and is relatively cool. The disk in such systems also becomes largely optically thin in the continuum, contributing to the total flux less than the stellar components of the system. In contrast, the viscosity and the temperature in spiral arms formed at the outer edge of the disk are higher and their contribution in continuum plays an increasingly important role. We model such disks and generate light curves which successfully simulate the observed double-humped light curves in the quiescence. Thanks to support of our programs by the Time Allocation Commission of OAN SPM, the perfect astroclimate in the observatory, and the phase-locked method of spectroscopic observations, the significant progress in the study of bounce-back systems using a small size telescope was reached.

  17. KIC 9406652: An Unusual Cataclysmic Variable in the Kepler Field of View

    CERN Document Server

    Gies, Douglas R; Howell, Steve B; Still, Martin D; Boyajian, Tabetha S; Hoekstra, Abe J; Jek, Kian J; LaCourse, Daryll; Winarski, Troy

    2013-01-01

    KIC 9406652 is a remarkable variable star in the Kepler field of view that shows both very rapid oscillations and long term outbursts in its light curve. We present an analysis of the light curve over quarters 1 to 15 and new spectroscopy that indicates that the object is a cataclysmic variable with an orbital period of 6.108 hours. However, an even stronger signal appears in the light curve periodogram for a shorter period of 5.753 hours, and we argue that this corresponds to the modulation of flux from the hot spot region in a tilted, precessing disk surrounding the white dwarf star. We present a preliminary orbital solution from radial velocity measurements of features from the accretion disk and the photosphere of the companion. We use a Doppler tomography algorithm to reconstruct the disk and companion spectra, and we also consider how these components contribute to the object's spectral energy distribution from ultraviolet to infrared wavelengths. This target offers us a remarkable opportunity to invest...

  18. Characterization of New Hard X-ray Cataclysmic Variables

    Science.gov (United States)

    Bernardini, F.; deMartino, D.; Falanga, M.; Mukai, K.; Matt, G.; Bonnet-Bidaud, J.-M.; Masetti, N.; Mouchet, M.

    2012-01-01

    Aims. We aim at characterizing a sample of nine new hard X-ray selected Cataclysmic Variable (CVs), to unambiguously identify them as magnetic systems of the Intermediate Polar (IP) type. Methods. We performed detailed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM-Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The broad band X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Results. Strong X-ray pulses at the White Dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGRJ08390-4833, IGRJ18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 poses a soft X-ray optically thick component at kT approx. 80 eV. An intense K (sub alpha) Fe line at 6.4 keV is detected in all sources. An absorption edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and lower limits to the accretion rates are also estimated. Conclusions. We found all sources to be IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors, while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535 display a disc-overflow accretion mode. All sources show a temperature gradient in the post-shock regions and a highly absorbed emission from material located in the pre-shock flow which is also responsible for the X-ray pulsations. Reflection at the WD surface is likely the origin of the fluorescent iron line. There is an increasing evidence for the presence of a warm absorber in IPs, a feature that needs future exploration. The addition of two systems to the subgroup of

  19. Physical parameters and orbital period variation of a newly discovered cataclysmic variable GSC 4560–02157

    Science.gov (United States)

    Han, Zhong-Tao; Qian, Sheng-Bang; Voloshina, Irina; Metlov, Vladimir G.; Zhu, Li-Ying; Li, Lin-Jia

    2016-10-01

    GSC 4560–02157 is a new eclipsing cataclysmic variable with an orbital period of 0.265359 days. By using the published V ‑ and R ‑ band data together with our observations, we discovered that the O ‑ C curve of GSC 4560–02157 may show a cyclic variation with a period of 3.51 years and an amplitude of 1.40 min. If this variation is caused by a light travel-time effect via the existence of a third body, then its mass can be derived as M 3 sin i' ≈ 91.08 M Jup, and it should be a low-mass star. In addition, several physical parameters were measured. The color of the secondary star was determined to be V ‑ R = 0.77(±0.03) which corresponds to a spectral type of K2–3. The secondary star's mass was estimated as M 2 = 0.73(±0.02) M ⊙ by combing the derived V ‑ R value around phase 0 with the assumption that it obeys the mass-luminosity relation for main sequence stars. This mass is consistent with the mass—period relation for CV donor stars. For the white dwarf, the eclipse durations and contacts of the white dwarf yield an upper limit on the white dwarf's radius corresponding to a lower limit on mass of M 1 ≈ 0.501 M ⊙. The overestimated radius and previously published spectral data indicate that the boundary layer may have a very high temperature.

  20. Roche tomography of cataclysmic variables - VII. The long-term magnetic activity of AE Aqr

    CERN Document Server

    Hill, C A; Steeghs, D; Dhillon, V S; Shahbaz, T

    2016-01-01

    We present a long-term study of the secondary star in the cataclysmic variable AE~Aqr, using Roche tomography to indirectly image starspots on the stellar surface spanning 8~years of observations. The 7 maps show an abundance of spot features at both high and low latitudes. We find that all maps have at least one large high-latitude spot region, and we discuss its complex evolution between maps, as well as its compatibility with current dynamo theories. Furthermore, we see the apparent growth in fractional spot coverage, $f_{\\mathrm{s}}$, around $45^{\\circ}$~latitude over the duration of observations, with a persistently high $f_{\\mathrm{s}}$ near latitudes of $20^{\\circ}$. These bands of spots may form as part of a magnetic activity cycle, with magnetic flux tubes emerging at different latitudes, similar to the `butterfly' diagram for the Sun. We discuss the nature of flux tube emergence in close binaries, as well as the activity of AE~Aqr in the context of other stars.

  1. Evolution of Cataclysmic Variables and Related Binaries Containing a White-Dwarf

    CERN Document Server

    Kalomeni, B; Rappaport, S; Molnar, M; Quintin, J; Yakut, K

    2016-01-01

    We present a binary evolution study of cataclysmic variables (CVs) and related systems with white dwarf accretors, including for example, AM CVn systems, classical novae, supersoft X-ray sources, and systems with giant donor stars. Our approach intentionally avoids the complications associated with population synthesis algorithms thereby allowing us to present the first truly comprehensive exploration of all of the subsequent binary evolution pathways that ZACVs might follow (assuming fully non-conservative, Roche-lobe overflow onto an accreting WD) using the sophisticated binary stellar evolution code MESA. The grid consists of 56,000 initial models, including 14 white dwarf accretor masses, 43 donor-star masses ($0.1-4.7$ $M_{\\odot}$), and 100 orbital periods. We explore evolution tracks in the orbital period and donor-mass ($P_{\\rm orb}-M_{\\rm don}$) plane in terms of evolution dwell times, masses of the white dwarf accretor, accretion rate, and chemical composition of the center and surface of the donor s...

  2. Roche tomography of cataclysmic variables - VI. Differential rotation of AE Aqr - Not tidally locked!

    CERN Document Server

    Hill, Colin; Shahbaz, Tariq; Steeghs, Danny; Dhillon, Vik

    2014-01-01

    We present Roche tomograms of the K4V secondary star in the cataclysmic variable AE Aqr, reconstructed from two datasets taken 9 days apart, and measure the differential rotation of the stellar surface. The tomograms show many large, cool starspots, including a large high-latitude spot and a prominent appendage down the trailing hemisphere. We find two distinct bands of spots around 22$^{\\circ}$ and 43$^{\\circ}$ latitude, and estimate a spot coverage of 15.4-17% on the northern hemisphere. Assuming a solar-like differential rotation law, the differential rotation of AE Aqr was measured using two different techniques. The first method yields an equator-pole lap time of 269 d and the second yields a lap time of 262 d. This shows the star is not fully tidally locked, as was previously assumed for CVs, but has a co-rotation latitude of $\\sim 40^{\\circ}$. We discuss the implications that these observations have on stellar dynamo theory, as well as the impact that spot traversal across the first Lagrangian point ma...

  3. Variable Star Network: World Center for Transient Object Astronomy and Variable Stars

    Science.gov (United States)

    Kato, Taichi; Uemura, Makoto; Ishioka, Ryoko; Nogami, Daisaku; Kunjaya, Chatief; Baba, Hajime; Yamaoka, Hitoshi

    2004-03-01

    Variable Star Network (VSNET) is a global professional-amateur network of researchers in variable stars and related objects, particularly in transient objects, such as cataclysmic variables, black-hole binaries, supernovae, and gamma-ray bursts. The VSNET has been playing a pioneering role in establishing the field of transient object astronomy, by effectively incorporating modern advances in observational astronomy and global electronic networks, as well as collaborative progress in theoretical astronomy and astronomical computing. The VSNET is now one of the best-featured global networks in this field of astronomy. We review the historical progress, design concept, associated technology, and a wealth of scientific achievements powered by VSNET.

  4. Observations of GAIA-identified Cataclysmic Variables Using the TUBITAK National Observatory

    Science.gov (United States)

    Esenoglu, Hasan H.; Kirbiyik, Halil; Kaynar, Suleyman; Okuyan, Oguzhan; Hamitoglu, Irek; Galeev, Almaz; Uluc, Kadir; Kocak, Murat; Kilic, Sila E.; Parmaksizoglu, Murat; Erece, Orhan; Ozisik, Tuncay; Gulsecen, Hulusi

    2016-07-01

    TUBITAK National Observatory supports the GAIA alerts with observations using three telescopes (RTT150, T100, T60) at the site with a limited time quota. We have observed 10 variable stars among GAIA sources discovered in the years 2014-2016 that may be candidate Cataclysmic Variables (CVs). Our TUG observations at this stage involve photometry and spectroscopy to aid the identification of these sources. The first preliminary result of our observations of Gaia14aat among them showed a dwarf nova outburst with an amplitude of 2.69 mag. We aim to construct a GAIA astrophysics group to study CVs along with supported studies using the SRG (Spectrum Roentgen Gamma astrophysical observatory) after the year of 2016. These observations will basically involve spectroscopy, narrow-band CCD imaging and photometry using several filters to aid the identification of these sources. RTT150 observations with very narrow filters (like H-alpha, SII, OIII with band width of range of 2 to 5 nm) will reveal whether shell around the SRG sources to aid identification novae among them.

  5. PHL 1445: An eclipsing cataclysmic variable with a substellar donor near the period minimum

    CERN Document Server

    McAllister, M J; Baraffe, I; Dhillon, V S; Marsh, T R; Bento, J; Bochinski, J; Bours, M C P; Breedt, E; Copperwheat, C M; Hardy, L K; Kerry, P; Parsons, S G; Rostron, J W; Sahman, D I; Savoury, C D J; Tunnicliffe, R L

    2015-01-01

    We present high-speed, three-colour photometry of the eclipsing dwarf nova PHL 1445, which, with an orbital period of 76.3 min, lies just below the period minimum of ~82 min for cataclysmic variable stars. Averaging four eclipses reveals resolved eclipses of the white dwarf and bright spot. We determined the system parameters by fitting a parameterised eclipse model to the averaged lightcurve. We obtain a mass ratio of q = 0.087 +- 0.006 and inclination i = 85.2 +- 0.9 degrees. The primary and donor masses were found to be Mw = 0.73 +- 0.03 Msun and Md = 0.064 +- 0.005 Msun, respectively. Through multicolour photometry a temperature of the white dwarf of Tw = 13200 +- 700 K and a distance of 220 +- 50 pc were determined. The evolutionary state of PHL 1445 is uncertain. We are able to rule out a significantly evolved donor, but not one that is slightly evolved. Formation with a brown dwarf donor is plausible; though the brown dwarf would need to be no older than 600 Myrs at the start of mass transfer, requirin...

  6. The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole Survey

    CERN Document Server

    Pretorius, M L; O'Donoghue, D; Henry, J P; Gioia, I M; Mullis, C R

    2007-01-01

    We use the ROSAT North Ecliptic Pole (NEP) survey to construct a small, but purely X-ray flux-limited sample of cataclysmic variable stars (CVs). The sample includes only 4 systems, 2 of which (RX J1715.6+6856 and RX J1831.7+6511) are new discoveries. We present time-resolved spectroscopy of the new CVs and measure orbital periods of 1.64 \\pm 0.02 h and 4.01\\pm 0.03 h for RX 1715.6+6856 and RX J1831.7+6511, respectively. We also estimate distances for all the CVs in our sample, based mainly on their apparent brightness in the infrared. The space density of the CV population represented by our small sample is (1.1 +2.3/-0.7) 10^-5 pc^-3. We can also place upper limits on the space density of any sub-population of CVs too faint to be included in the NEP survey. In particular, we show that if the overall space density of CVs is as high as 2 10^-4 pc^-3 (as has been predicted theoretically), the vast majority of CVs must be fainter than L_X \\simeq 2 10^29 erg/s.

  7. ULTRACAM photometry of the eclipsing cataclysmic variables XZ Eri and DV UMa

    CERN Document Server

    Feline, W J; Marsh, T R; Brinkworth, C S

    2004-01-01

    We present high-speed, three-colour photometry of the faint eclipsing cataclysmic variables XZ Eri and DV UMa. We determine the system parameters through two techniques: first, timings of the eclipse contact phases of the white dwarf and bright-spot using the derivative of the light curve; and secondly, a parameterized model of the eclipse fitted to the observed light curve by chi-squared minimisation. For both objects, we prefer the latter method, as it is less affected by photon noise and rapid flickering. For XZ Eri we obtain a mass ratio q = 0.1098 +/- 0.0017 and an orbital inclination i = 80.16 +/- 0.09 degrees. For DV UMa we derive figures of q = 0.1506 +/- 0.0009 and i = 84.24 +/- 0.07 degrees. The secondary star in XZ Eri has a very low mass Mr/Msun = 0.0842 +/- 0.0024, placing it close to the upper limit on the mass of a brown dwarf.

  8. ULTRACAM photometry of the eclipsing cataclysmic variables GY Cnc, IR Com and HT Cas

    CERN Document Server

    Feline, W J; Marsh, T R; Watson, C A; Littlefair, S P

    2005-01-01

    We present high-speed, three-colour photometry of the eclipsing cataclysmic variables GY Cnc, IR Com and HT Cas. We find that the sharp eclipses in GY Cnc and IR Com are due to eclipses of the white dwarf. There is some evidence for a bright spot on the edge of the accretion disc in GY Cnc, but not in IR Com. Eclipse mapping of HT Cas is presented which shows changes in the structure of the quiescent accretion disc. Observations in 2002 show the accretion disc to be invisible except for the presence of a bright spot at the disc edge. 2003 observations, however, clearly show a bright inner disc and the bright spot to be much fainter than in 2002. Although no outburst was associated with either set of quiescent observations, the system was ~0.6 mJy brighter in 2003, mainly due to the enhanced emission from the inner disc. We propose that these changes are due to variations in the mass transfer rate from the secondary star and through the disc. The disc colours indicate that it is optically thin in both its inne...

  9. The newly discovered eclipsing cataclysmic star 2MASS J16211735 + 4412541 and its peculiarity

    Science.gov (United States)

    Kjurkchieva, Diana P.; Popov, Velimir A.; Vasileva, Doroteya L.; Petrov, Nikola I.

    2017-04-01

    We present our observations of the newly discovered, eclipsing cataclysmic star 2MASS J16211735 + 4412541 carried out two weeks after its outburst at the beginning of June 2016. Its main peculiarity is the big increasing of eclipse depth during outburst. We qualitatively modelled the folded light curves at quiescence and outburst in order to explain the reason for increase of the primary luminosity about two hundred times. The light curve fits revealed that such an effect can be reproduced by a flat disc whose radius and temperature are several times bigger than those of the primary at quiescence.

  10. The long-term light curve of the cataclysmic variable V794 Aquilae

    Energy Technology Data Exchange (ETDEWEB)

    Honeycutt, R. K. [Astronomy Department, Indiana University, Swain Hall West, Bloomington, IN 47405 (United States); Kafka, S. [Department of Terrestrial Magnetism, Carnegie Inst. of Washington, 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Robertson, J. W., E-mail: honey@astro.indiana.edu, E-mail: skafka@aip.org, E-mail: Jeff.Robertson@atu.edu [Arkansas Tech University, Department of Physical Sciences, 1701 N. Boulder, Russellville, AR 72801-2222 (United States)

    2014-01-01

    The 1990-2012 light curve of the nova-like (NL) cataclysmic variable V794 Aql is studied in order to characterize and better understand the transitions to and from the faint state, and the variations within the bright state. Investigations of earlier portions of this data had concluded that the transitions to the low state were much slower than the rapid recovery, giving a sawtoothed appearance to the light curve. This behavior differs from that of most other VY Scl stars, which led to an interpretation of the large amplitude sawtooths as being due to an accretion disk (AD) instability. However, more recent photometry strongly suggests that the bright state itself has transitions of 1-1.5 mag, and that earlier studies had intermixed these bright state variations with the transitions to the low state. These newly recognized variations within the bright state sometimes appear as small outbursts (OBs) with typical amplitudes of 0.5-1.5 mag and spacings of ∼15-50 days. The rise times of the OBs are 2-3 times faster than the decline times. We argue that the V794 Aql bright state variations are due to AD behavior similar to that seen in dwarf novae, but with varying degrees of stability. Similar regular small OBs have also been reported in other NL CVs, which we compare with V794 Aql. The true deep low states in V794 Aql appear to be normal, having transition speeds and shapes very similar to the transitions in other VY Scl stars.

  11. A Far-Ultraviolet Survey of 47 Tucanae.II The Long-Period Cataclysmic Variable AKO 9

    CERN Document Server

    Knigge, C; Shara, M M; Long, K S; Gilliland, R L; Knigge, Christian; Zurek, David. R.; Shara, Michael M.; Long, Knox S.; Gilliland, Ronald L.

    2003-01-01

    We present time-resolved, far-ultraviolet (FUV) spectroscopy and photometry of the 1.1 day eclipsing binary system AKO 9 in the globular cluster 47 Tucanae. AKO 9's FUV spectrum is blue and exhibits prominent C IV and He II emission lines. The spectrum broadly resembles that of long-period, cataclysmic variables in the galactic field. Combining our time-resolved FUV data with archival optical photometry of 47 Tuc, we refine AKO 9's orbital period and define an accurate ephemeris for the system. We also place constraints on several other system parameters, using a variety of observational constraints. We find that all of the empirical evidence is consistent with AKO 9 being a long-period dwarf nova in which mass transfer is driven by the nuclear expansion of a sub-giant donor star. We therefore conclude that AKO 9 is the first spectroscopically confirmed cataclysmic variable in 47 Tuc. We also briefly consider AKO 9's likely formation and ultimate evolution. Regarding the former, we find that the system was al...

  12. Archival Ultraviolet Spectroscopic Analysis of Disk-Dominated Cataclysmic Variables: The Importance of the Boundary Layer

    Science.gov (United States)

    Godon, Patrick

    We propose to carry out a systematic ultraviolet (UV) spectral analysis of 43 disk- dominated systems in cataclysmic variable (CV) binaries with the inclusion of the contribution from the boundary layer, from NASA UV Space Missions such as HST, FUSE, HUT, IUE and ORFEUS. The mass accretion in CVs is a badly needed parameter to verify the theory of the evolution of CVs, to understand the accretion process itself and the disk instability. However, many disk-dominated systems unexpectedly prove impossible to model using only standard accretion disks and white dwarfs in combination. Our objective is to overcome this difficulty by modeling the UV spectrum of the boundary layer between the star and disk, including its effect on the spectrum of the disk and star for the first time. This will provide the first step needed for the improvement of the disk model in UV spectroscopic analysis of disk-dominated systems in CVs. At the same time the results of this spectral analysis will provide information on the boundary layer and accretion disk of these systems. As a by-product, we will create a web-based catalog of all the archival UV spectra of disk-dominated CVs, which will be added and fused to our existing and growing web-based catalog of FUSE spectra of CVs. Since the WD is the most common end-product of stellar evolution (approx 90% of all the stars in the Galaxy have or will evolve into white dwarfs), and the accretion disk is the most common universal structure resulting from mass transfer with angular momentum, and since both can be directly viewed in CVs in the ultraviolet (UV), an understanding of the consequences of accretion in these systems is the first step in a global understanding of accretion in other systems throughout the universe. These include Young Stellar Objects, galactic binaries (accretion onto neutron stars and black holes) and the most difficult to study, Active Galactic Nuclei. In addition, the formation history of WDs is closely linked to the

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

    CERN Document Server

    Oliveira, A S; Cieslinski, D; Jablonski, F J; Silva, K M G; Almeida, L A; Rodriguez-Ardila, A; Palhares, M S

    2016-01-01

    The increasing number of synoptic surveys made by small robotic telescopes, as the photometric Catalina Real-Time Transient Survey (CRTS), represents a unique opportunity for the discovery of new variable objects, improving the samples of many classes of variables. Our goal is the discovery of new magnetic Cataclysmic Variables (mCVs). They are rare objects, which probe interesting accretion scenarios controlled by the white-dwarf magnetic field. We performed an optical spectroscopic survey to search for signatures of magnetic accretion on 47 variable objects selected mostly from CRTS. Our sample includes 13 polar strong candidates, from which 5 are new discoveries. Accretion disks seem to be present in other 19 objects. One is a previously known probable intermediate polar. We suggest 8 other objects could also be of this class. In particular, 7 of them have spectra consistent with short-period intermediate polars. We suggest one object is a novalike of the VY~Scl class. We also caught one dwarf nova in erup...

  14. [Data mining for cataclysmic variables candidates in SDSS-DR8].

    Science.gov (United States)

    Jiang, Bin; Pan, Jing-Chang; Wang, Wei

    2013-02-01

    An automatic and efficient method for cataclysmic variables candidates is presented in this paper. The nonlinear locally linear embedding-LLE method is applied in the newly released SDSS-DR8 spectra. Spectra are dimension-reduced by LLE and classified by artificial neural network. The greatly reduced final candidates can be identified manually. 6 new CVs candidates were found in the experiment, and the compare between LLE with PCA shows the feasibility of nonlinear method in data mining in astronomical data.

  15. MOCCA-SURVEY Database I. Accreting White Dwarf Binary Systems in Globular Clusters I. Cataclysmic Variables -- present-day population

    CERN Document Server

    Belloni, Diogo T; Askar, Abbas; Leigh, Nathan; Hypki, Arkadiusz

    2016-01-01

    In this paper, which is the first in a series of papers associated with cataclysmic variables and related objects, we introduce the CATUABA code, a numerical machinery written for analysis of the MOCCA simulations, and show some first results by investigating the present-day population of cataclysmic variables in globular clusters. Emphasis was given on their properties and the observational selection effects when observing and detecting them. In this work we analysed in this work six models, including three with Kroupa distributions of the initial binaries. We found that for models with Kroupa initial distributions, considering the standard value of the efficiency of the common envelope phase adopted in BSE, no single cataclysmic variable was formed only via binary stellar evolution, i. e., in order to form them, strong dynamical interactions have to take place. We show and explain why this is inconsistent with observational and theoretical results. Our results indicate that the population of cataclysmic var...

  16. Gaia and Variable Stars

    CERN Document Server

    Udalski, A; Skowron, D M; Skowron, J; Pietrukowicz, P; Mróz, P; Poleski, R; Szymański, M K; Kozłowski, S; Wyrzykowski, Ł; Ulaczyk, K; Pawlak, M

    2016-01-01

    We present a comparison of the Gaia DR1 samples of pulsating variable stars - Cepheids and RR Lyrae type - with the OGLE Collection of Variable Stars aiming at the characterization of the Gaia mission performance in the stellar variability domain. Out of 575 Cepheids and 2322 RR Lyrae candidates from the Gaia DR1 samples located in the OGLE footprint in the sky, 559 Cepheids and 2302 RR Lyrae stars are genuine pulsators of these types. The number of misclassified stars is low indicating reliable performance of the Gaia data pipeline. The completeness of the Gaia DR1 samples of Cepheids and RR Lyrae stars is at the level of 60-75% as compared to the OGLE Collection dataset. This level of completeness is moderate and may limit the applicability of the Gaia data in many projects.

  17. 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

  18. 1H 1752 + 081: an eclipsing cataclysmic variable with a small accretion disk

    Science.gov (United States)

    Silber, Andrew D.; Remillard, Ronald A.; Horne, Keith; Bradt, Hale V.

    1994-04-01

    We announce the discovery of an eclipsing nova-like cataclysmic variable (CV) as the optical counterpart to the HEAO 1 X-ray source 1H1752 + 081. This CV has an orbital period of 1.882801 hr, a high equivalent width of H-beta, and an average mv of 16.4 out of the eclipse. A geometric model is constructed from observations of the eclipse ingress and egress in many optical bandpasses. The broad-band emission originates primarily in two regions; the disk/accretion stream 'hot spot' and a compact central component, which may be a spot on the white dwarf surface, the entire white dwarf surface or the boundary layer between the accretion disk and the white dwarf surface. Based on the durations and offsets of the two eclipses we determined the mass ratio q = 2.5 +/- 0.6 and the angle of inclination i = 77 deg +/- 2 deg. If the central component is the entire white dwarf surface the masses of the stars are M1 = 0.80 +/- 0.06 solar masses and M2 = 0.32 +/- 0.06 solar masses. The disk is faint and small (RD = 0.25 +/- 0.05 rL1, where rL1 is the distance from the primary to the L1 point), compared to other eclipsing CVs. The small disk may result from the removal of angular momentum from the accretion disk by the magnetic field of the white dwarf; this CV may be a DQ Her type with a slowly rotating white dwarf. The emission-line velocities do not show the 'Z-wave' expected from the eclipse of a Keplerian accretion disk, nor do they have the correct phasing to originate near the white dwarf. The most likely origin of the line emission is the hot spot. The secondary star is visible at wavelengths greater than or equal to 6000 A during eclipse. We estimate a spectral type approximately M6 which, together with the observed m1 = 16.94 during eclipse, results in a distance estimate of 150 +/- 27 pc.

  19. First Spitzer Space Telescope Observations of Magnetic Cataclysmic Variables: Evidence for Excess Emission at 3--8 microns

    CERN Document Server

    Howell, S B; Hoard, D W; Wachter, S; Harrison, T; Thomas, H C B; Stefaniak, L; Ciardi, D R; Szkody, P; Van Belle, G T; Howell, Steve B.; Brinkworth, Carolyn; Wachter, Stefanie; Harrison, Thomas; Thomas, Howard Chun Beth; Stefaniak, Linda; Ciardi, David R.; Szkody, Paula; Belle, Gerard van

    2006-01-01

    We present the first observations of magnetic cataclysmic variables with the Spitzer Space Telescope. We used the Infrared Array Camera to obtain photometry of the polars EF Eri, GG Leo, V347 Pav, and RX J0154.0-5947 at 3.6, 4.5, 5.8, and 8.0 $\\mu$m. In all of our targets, we detect excess mid-infrared emission over that expected from the component stars alone. We explore the origin of this IR excess by examining bremsstrahlung, cyclotron emission, circumbinary dust, and L/T brown dwarf secondary stars. Bremsstrahlung and cyclotron emission appear unlikely to be significant contributors to the observed fluxes. At present, the most likely candidate for the excess emission is dust that is probably located in a circumbinary disk with an inner temperature near 800 K. However, a simple dust disk plus any reasonable low mass or brown dwarf-like secondary star is unable to fully explain the observed flux densities in the 3--8 $\\mu$m region.

  20. On the origin of the peculiar cataclysmic variable AE Aquarii

    CERN Document Server

    Beskrovnaya, N G

    2014-01-01

    The nova-like variable AE Aquarii is a close binary system containing a red dwarf and a magnetized white dwarf rotating with the period of 33 seconds. A short spin period of the white dwarf is caused by an intensive mass exchange between the system components during a previous epoch. We show that a high rate of disk accretion onto the white dwarf surface resulted in temporary screening of its magnetic field and spin-up of the white dwarf to its present spin period. Transition of the white dwarf to the ejector state occurred at a final stage of the spin-up epoch after its magnetic field had emerged from the accreted plasma due to diffusion. In the frame of this scenario AE Aqr represents a missing link in the chain of Polars evolution and the white dwarf resembles a recycled pulsar.

  1. Boundary-layer temperatures in high accretion rate cataclysmic variables

    Energy Technology Data Exchange (ETDEWEB)

    Hoare, M.G.; Drew, J.E. (Oxford Univ. (UK). Dept. of Physics Oxford Univ. (UK). Dept. of Astrophysics)

    1991-04-01

    We use the Zanstra method to derive limits on boundary-layer temperatures in eclipsing dwarf novae during outburst and nova-like variables, using the observed He II {lambda}1640 and {lambda}4686 recombination lines. It is assumed that all the emission is produced in the wind rather than the accretion disc. This method constrains the boundary-layer temperatures to between 50 000 and 100 000 K depending on the degree of wind bipolarity. These estimates are lower than the T>or approx200 000 K predicted theoretically. Possible explanations include rapid rotation of the white dwarf and spreading of the boundary layer over the entire white-dwarf surface. (author).

  2. Variable Star Network: World Center for Transient Object Astronomy and Variable Stars

    CERN Document Server

    Kato, T; Ishioka, R; Nogami, D; Kunjaya, C; Baba, H; Yamaoka, H

    2003-01-01

    Variable Star Network (VSNET, http://www.kusastro.kyoto-u.ac.jp/vsnet/) is a global professional-amateur network of researchers in variable stars and related objects, particularly in transient objects, such as cataclysmic variables, black hole binaries, supernovae and gamma-ray bursts. The VSNET has been playing a pioneering role in establishing the field of "transient object astronomy", by effectively incorporating modern advance in observational astronomy and global electronic network, as well as collaborative progress in theoretical astronomy and astronomical computing. The VSNET is now one of the best-featured global networks in this field of astronomy. We review on the historical progress, design concept, associated technology, and a wealth of scientific achievements powered by the VSNET.

  3. AN ONLINE CATALOG OF CATACLYSMIC VARIABLE SPECTRA FROM THE FAR-ULTRAVIOLET SPECTROSCOPIC EXPLORER

    Energy Technology Data Exchange (ETDEWEB)

    Godon, Patrick; Sion, Edward M. [Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States); Levay, Karen [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Linnell, Albert P.; Szkody, Paula [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Barrett, Paul E. [United States Naval Observatory, Washington, DC 20392 (United States); Hubeny, Ivan [Steward Observatory and Department of Astronomy and Astrophysics, University of Arizona, Tucson, AZ 85721 (United States); Blair, William P., E-mail: patrick.godon@villanova.edu, E-mail: edward.sion@villanova.edu, E-mail: klevay@stsci.edu, E-mail: linnell@astro.washington.edu, E-mail: szkody@astro.washington.edu, E-mail: barrett.paul@usno.navy.mil, E-mail: hubeny@as.arizona.edu, E-mail: wpb@pha.jhu.edu [Henry A. Rowland Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218 (United States)

    2012-12-15

    We present an online catalog containing spectra and supporting information for cataclysmic variables that have been observed with the Far-Ultraviolet Spectroscopic Explorer (FUSE). For each object in the catalog we list some of the basic system parameters such as (R.A., decl.), period, inclination, and white dwarf mass, as well as information on the available FUSE spectra: data ID, observation date and time, and exposure time. In addition, we provide parameters needed for the analysis of the FUSE spectra such as the reddening E(B - V), distance, and state (high, low, intermediate) of the system at the time it was observed. For some of these spectra we have carried out model fits to the continuum with synthetic stellar and/or disk spectra using the codes TLUSTY and SYNSPEC. We provide the parameters obtained from these model fits; this includes the white dwarf temperature, gravity, projected rotational velocity, and elemental abundances of C, Si, S, and N, together with the disk mass accretion rate, the resulting inclination, and model-derived distance (when unknown). For each object one or more figures are provided (as gif files) with line identification and model fit(s) when available. The FUSE spectra and the synthetic spectra are directly available for download as ASCII tables. References are provided for each object, as well as for the model fits. In this article we present 36 objects, and additional ones will be added to the online catalog in the future. In addition to cataclysmic variables, we also include a few related objects, such as a wind-accreting white dwarf, a pre-cataclysmic variable, and some symbiotics.

  4. On the long term evolution of white dwarfs in cataclysmic variables and their recurrence times

    Science.gov (United States)

    Sion, E. M.; Starrfield, S. G.

    1985-01-01

    The relevance of the long term quasi-static evolution of accreting white dwarfs to the outbursts of Z Andromeda-like symbiotics; the masses and accretion rates of classical nova white dwarfs; and the observed properties of white dwarfs detected optically and with IUE in low M dot cataclysmic variables is discussed. A surface luminosity versus time plot for a massive, hot white dwarf bears a remarkable similarity to the outburst behavior of the hot blue source in Z Andromeda. The long term quasi-static models of hot accreting white dwarfs provide convenient constraints on the theoretically permissible parameters to give a dynamical (nova-like) outburst of classic white dwarfs.

  5. Cataclysmic Variables From the Sloan Digital Sky Survey. VI. the Sixth Year (2005)

    Energy Technology Data Exchange (ETDEWEB)

    Szkody, Paula; /Washington U., Seattle, Astron. Dept.; Henden, Arne; /Naval Observ., Flagstaff /AAVSO, Cambridge; Mannikko, Lee; Mukadam, Anjum; /Washington U., Seattle,; Schmidt, Gary D.; /Arizona U., Astron. Dept. - Steward Observ.; Bochanski, John J.; Agueros, Marcel; Anderson, Scott F.; Silvestri, Nicole M.; /Washington U., Seattle,; Dahab, William E.; /Princeton U. Observ.; Oguri, Masamune; /Princeton U. Observ. /KIPAC, Menlo Park; Schneider, Donald P.; /Penn State U., Astron. Astrophys.; Shin,; Strauss, Michael A.; Knapp, Gillian R.; /Princeton U. Observ.; West, Andrew A.; /Washington U., Seattle, Astron. Dept.

    2007-06-15

    The 28 cataclysmic variables found in 2005 in the Sloan Digital Sky Survey are presented with their coordinates, magnitudes and spectra. Five of these systems are previously known CVs (HH Cnc, SX LMi, QZ Ser, RXJ1554.2+2721 and HS1016+3412) and the rest are new discoveries. Additional spectroscopic, photometric and/or polarimetric observations of 10 systems were carried out, resulting in estimates of the orbital periods for seven of the new binaries. The 23 new CVs include one eclipsing system, one new Polar and five systems whose spectra clearly reveal atmospheric absorption lines from the underlying white dwarf.

  6. Substellar secondaries in zero-age cataclysmic variables

    Directory of Open Access Journals (Sweden)

    M. Politano

    2004-01-01

    Full Text Available Se investiga la formaci on actual de variables catacl smicas (CVs con secundarias de enanas marrones (BD utilizando la t ecnica de s ntesis de poblaci on. En el c odigo de s ntesis de poblaci on se incorporaron resultados de los ultimos modelos detallados para las BDs. Encontramos que CVs de edad cero (ZACVs con secundarias BDs poseen per odos orbitales comprendidos en el intervalo 46 min { 2.5 horas, formando el 18% del total de la poblaci on actual de ZACVs. Por lo tanto encontramos que el 15% de la poblaci on actual de ZACVs deber a tener per odos orbitales m as cortos que el per odo orbital m nimo observado para CVs. Investigamos tambi en la dependencia de la tasa actual de formaci on de CVs con secundarias BD con el valor asumido del par ametro de e ciencia de la envolvente com un CE, asumiendo tres distribuciones de cociente de masas diferentes para binarias ZAMS. Encontramos que el proceso de la envolvente com un debe de ser extremadamente ine ciente ( CE < 0:1 como para que no se formen CVs con BD secundarias. Finalmente encontramos que las binarias progenitoras de ZACVs con secundarias BD poseen separaciones orbitales < 3AU y masas primarias entre 1 y 10 M con 75% de las masas primarias menores que 1.6 M . Es interesante se~nalar que estos intervalos en separaci on orbital y masa primaria colocan a la mayor a de estas binarias progenitoras dentro del llamado \\desierto de enanas marrones".

  7. Emission line tomography of the short period cataclysmic variables CC Scl and V2051 Oph

    CERN Document Server

    Longa-Peña, P; Marsh, T

    2014-01-01

    We present time-series spectroscopy of two short period cataclysmic variables, CC Scl and V2051 Oph, to test the efficiency of Doppler tomography-based methods in constraining orbital parameters of evolved cataclysmic variables. We find that the Ca~II triplet lines offer superior diagnostics, revealing emission components from the mass donors and sharp images of the accretion discs. Furthermore, we use Monte-Carlo methods to estimate the uncertainties from ensembles of Doppler maps. We compare our new methods against traditional radial velocity methods and show that they offer a valid route towards system parameter determination. Our analysis of CC Scl suggests a low mass ratio of $q=0.08\\pm0.03$ with a primary velocity of $K_1=37\\pm14$ km/s. This mass ratio is in between the pre- and post-period minimum status, however our $K_1$ solution favours a post-period minimum system. Our derived parameters for V2051 Oph ($q= 0.16\\pm 0.03$, $K_1=97\\pm10$ km/s) are in agreement with the eclipse solution ($q=0.19\\pm0.03...

  8. Spectroscopic Orbital Periods for 29 Cataclysmic Variables from the Sloan Digital Sky Survey

    CERN Document Server

    Thorstensen, John R; Peters, Christopher S; Skinner, Julie N; Southworth, John; Gaensicke, Boris T

    2015-01-01

    We report follow-up spectroscopy of 29 cataclysmic variables from the Sloan Digital Sky Survey (SDSS), 22 of which were discovered by SDSS and seven other previously known systems that were recovered in SDSS. The periods for 16 of these objects were included in the tabulation by Gaensicke et al. (2009). While most of the systems have periods less than 2 hours, only one has a period in the 80-86 minute 'spike' found by Gaensicke et al. (2009), and 11 have periods longer than 3 hours, indicating that the present sample is skewed toward longer-period, higher-luminosity objects. Seven of the objects have spectra resembling dwarf novae, but have apparently never been observed in outburst, suggesting that many cataclysmics with relatively low variability amplitude remain to be discovered. Some of the objects are notable. SDSS J07568+0858 and SDSS J08129+1911 were previously known to have deep eclipses; in addition to spectroscopy, we use archival data from the CRTTS to refine their periods. We give a parallax-based...

  9. Evolution of accretion disc flow in cataclysmic variables. 3. Outburst properties of constant and uniform-. cap alpha. model discs

    Energy Technology Data Exchange (ETDEWEB)

    Lin, D.N.C.; Faulkner, J. (Lick Observatory, Santa Cruz, CA (USA); California Univ., Santa Cruz (USA). Board of Studies in Astronomy and Astrophysics); Papaloizou, J. (Queen Mary Coll., London (UK). Dept. of Applied Mathematics)

    1985-01-01

    The investigation of accretion disc models relevant to cataclysmic-variable systems is continued. This paper examines the stability and evolution of some simple accretion disc models in which the viscosity is prescribed by an ad hoc uniform-..cap alpha.. model. It is primarily concerned with systems in which the mass-input rate from the secondary to the disc around the primary is assumed to be constant. However, initial calculations with variable mass-input rates are also performed. The time-dependent visual magnitude light-curves are constructed for cataclysmic binaries with a range of disc size, primary mass, mass-input rate, and magnitude of viscosity.

  10. Barnes-Evans relations for dwarfs with an application to the determination of distances to cataclysmic variables

    CERN Document Server

    Beuermann, K

    2006-01-01

    Barnes-Evans type relations provide an empirical relationship between the surface brightness of stars and their color. They are widely used for measuring the distances to stars of known radii, as the Roche-lobe filling secondaries in cataclysmic variables (CVs). The calibration of the surface brightness of field dwarfs of near-solar metalicity with spectral types A0 to L8 covers all secondary spectral types detectable in CVs and related objects and will aid in the measurement of their distances. The calibrations are based on the radii of field dwarfs measured by the Infrared Flux Method and by interferometry. Published photometry is used and homogenized to the Cousins Rc and Ic and the CIT JHK photometric systems. The narrow band surface brightness at 7500A is based on our own and published spectrophotometry. Care is taken to select the dwarfs for near-solar metalicity, appropriate to CVs, and to avoid errors caused by unrecognized binarity. Relations are provided for the surface brightness in V, Rc, Ic, J, H...

  11. A Critical Examination of the Paradigm for the 2-3 Hour Period Gap in Cataclysmic Variables

    CERN Document Server

    Howell, S B; Rappaport, S; Howell, Steve B.; Nelson, Lorne A.

    2000-01-01

    We critically examine the basic paradigm for the origin of the 2-3 hr period gap in cataclysmic variables (CVs). We carry out an extensive population synthesis study of CVs starting from ~ 3 x 10^6 primordial binaries, and evolving some ~ 2 x 10^4 surviving systems through their CV phase. In particular we study current-epoch distributions of CVs in the $\\dot M-P_{orb}$, R_{2}-P_{orb}, M_{2}-P_{orb}, q-P_{orb}, T_{eff}-P_{orb}, and L_{2}-P_{orb} planes, where $\\dot M$ is the mass transfer rate, q is the mass ratio M_2/M_1, and M_2, R_2, T_{eff}, and L_2 are the donor star mass, radius, effective temperature, and luminosity, respectively. This work presents a new perspective on theoretical studies of the long-term evolution of CVs. In particular, we show that if the current paradigm is correct, the secondary masses in CVs just above the period gap should be as much as ~ 50% lower than would be inferred if one assumes a main-sequence radius-mass relation for the donor star.

  12. MASTER OT J190519.41+301524.4: New Eclipsing Cataclysmic Variable of VY Scl Type

    CERN Document Server

    Martinelli, F

    2016-01-01

    MASTER OT J190519.41+301524.4 was discovered as an optical transient of 15.7m by the Mobile Astronomical System of TElescope-Robots in March 2014. We report the results of photometric observations of this variable performed at Lajatico Astronomical Center in June-July 2015. The light curve is showing deep V-shaped eclipses with an amplitude of two magnitudes. The orbital period was determined to be 0.129694 d (3.113 h). Based on the archival observations and the shape of the orbital curve we suggest that MASTER OT J190519.41+301524.4 is a new cataclysmic variable of VY Scl type ("anti-nova") with an inclination angle close to 90 deg.

  13. Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs): I. The Importance of Spiral Shocks

    CERN Document Server

    Ju, Wenhua; Zhu, Zhaohuan

    2016-01-01

    We present results from the first global 3D MHD simulations of accretion disks in Cataclysmic Variable (CV) systems in order to investigate the relative importance of angular momentum transport via turbulence driven by the magnetorotational instability (MRI) compared to that driven by spiral shock waves. Remarkably, we find that even with vigorous MRI turbulence, spiral shocks are an important component to the overall angular momentum budget, at least when temperatures in the disk are high (so that Mach numbers are low). In order to understand the excitation, propagation, and damping of spiral density waves in our simulations more carefully, we perform a series of 2D global hydrodynamical simulations with various equation of states and both with and without mass inflow via the Lagrangian point (L1). Compared with previous similar studies, we find the following new results. 1) Linear wave dispersion relation fits the pitch angles of spiral density waves very well. 2) We demonstrate explicitly that mass accreti...

  14. Statistical properties of dwarf novae-type cataclysmic variables: The Outburst Catalogue

    CERN Document Server

    Coppejans, Deanne L; Knigge, Christian; Pretorius, Margaretha L; Woudt, Patrick A; Groot, Paul J; Van Eck, Cameron L; Drake, Andrew J

    2015-01-01

    The Outburst Catalogue contains a wide variety of observational properties for 722 dwarf nova-type (DN) cataclysmic variables (CVs) and 309 CVs of other types from the Catalina Real-time Transient Survey. In particular, it includes the apparent outburst and quiescent V-band magnitudes, duty cycles, limits on the recurrence time, upper- and lower-limits on the distance and absolute quiescent magnitudes, colour information, orbital parameters, and X-ray counterparts. These properties were determined by means of a classification script presented in this paper. The DN in the catalogue show a correlation between the outburst duty cycle and the orbital period (and outburst recurrence time), as well as between the quiescent absolute magnitude and the orbital period (and duty cycle). This is the largest sample of dwarf nova properties collected to date. Besides serving as a useful reference for individual systems and a means of selecting objects for targeted studies, it will prove valuable for statistical studies tha...

  15. A 6.3-h superhump in the cataclysmic variable TV Columbae the longest yet seen

    CERN Document Server

    Retter, A; Augusteijn, T; Naylor, T; Bedding, T R; Bembrick, C; McCormick, J; Velthuis, F

    2002-01-01

    We present results from a two week multi-longitude photometric campaign on TV Col held in 2001 January. The data confirm the presence of a permanent positive superhump found in re-examination of extensive archive photometric data of TV Col. The 6.3-h period is 15 per cent longer than the orbital period and obeys the well known relation between superhump period excess and binary period. At 5.5-h, TV Col has an orbital period longer than any known superhumping cataclysmic variable and, therefore, a mass ratio which might be outside the range at which superhumps can occur according to the current theory. We suggest several solutions for this problem.

  16. Two Rare Magnetic Cataclysmic Variables with Extreme Cyclotron Features Identified in the Sloan Digital Sky Survey

    CERN Document Server

    Szkody, P; Schmidt, G; Hall, P B; Margon, B; Miceli, A; Subba-Rao, M; Frith, W J; Harris, H; Szkody, Paula; Anderson, Scott F.; Schmidt, Gary; Hall, Patrick B.; Margon, Bruce; Miceli, Antonino; Rao, Mark Subba; Frith, James; Harris, Hugh

    2003-01-01

    Two newly identified magnetic cataclysmic variables discovered in the Sloan Digital Sky Survey (SDSS), SDSSJ155331.12+551614.5 and SDSSJ132411.57+032050.5, have spectra showing highly prominent, narrow, strongly polarized cyclotron humps with amplitudes that vary on orbital periods of 4.39 and 2.6 hrs, respectively. In the former, the spacing of the humps indicates the 3rd and 4th harmonics in a magnetic field of ~60 MG. The narrowness of the cyclotron features and the lack of strong emission lines imply very low temperature plasmas and very low accretion rates, so that the accreting area is heated by particle collisions rather than accretion shocks. The detection of rare systems like these exemplifies the ability of the SDSS to find the lowest accretion rate close binaries.

  17. Using Gaussian processes to model light curves in the presence of flickering: the eclipsing cataclysmic variable ASASSN-14ag

    CERN Document Server

    McAllister, M J; Dhillon, V S; Marsh, T R; Ashley, R P; Bours, M C P; Breedt, E; Hardy, L K; Hermes, J J; Kengkriangkrai, S; Kerry, P; Rattanasoon, S; Sahman, D I

    2016-01-01

    The majority of cataclysmic variable (CV) stars contain a stochastic noise component in their light curves, commonly referred to as flickering. This can significantly affect the morphology of CV eclipses and increases the difficulty in obtaining accurate system parameters with reliable errors through eclipse modelling. Here we introduce a new approach to eclipse modelling, which models CV flickering with the help of Gaussian processes (GPs). A parameterised eclipse model - with an additional GP component - is simultaneously fit to 8 eclipses of the dwarf nova ASASSN-14ag and system parameters determined. We obtain a mass ratio $q$ = 0.149 $\\pm$ 0.016 and inclination $i$ = 83.4 $^{+0.9}_{-0.6}$ $^{\\circ}$. The white dwarf and donor masses were found to be $M_{w}$ = 0.63 $\\pm$ 0.04 $M_{\\odot}$ and $M_{d}$ = 0.093 $^{+0.015}_{-0.012}$ $M_{\\odot}$, respectively. A white dwarf temperature $T_{w}$ = 14000 $^{+2200}_{-2000}$ K and distance $d$ = 146 $^{+24}_{-20}$ pc were determined through multicolour photometry. W...

  18. Orbital periods of cataclysmic variables identified by the SDSS. IX. NTT photometry of eight eclipsing and three magnetic systems

    CERN Document Server

    Southworth, John; Gaensicke, B T; Copperwheat, C M

    2014-01-01

    We report the discovery of eclipses and the first orbital period measurements for four cataclysmic variables, plus the first orbital period measurements for one known eclipsing and two magnetic systems. SDSS J093537.46+161950.8 exhibits 1-mag deep eclipses with a period of 92.245 min. SDSS J105754.25+275947.5 has short and deep eclipses and an orbital period of 90.44 min. Its light curve has no trace of a bright spot and its spectrum is dominated by the white dwarf component, suggesting a low mass accretion rate and a very low-mass and cool secondary star. CSS J132536+210037 shows 1-mag deep eclipses each separated by 89.821 min. SDSS J075653.11+085831.8 shows 2-mag deep eclipses on a period of 197.154 min. CSS J112634-100210 is an eclipsing dwarf nova identified in the Catalina Real Time Transit Survey, for which we measure a period of 111.523 min. SDSS J092122.84+203857.1 is a magnetic system with an orbital period of 84.240 min; its light curve is a textbook example of cyclotron beaming. A period of 158.72...

  19. XMM-Newton observations of the low-luminosity cataclysmic variable V405 Pegasi

    CERN Document Server

    Schwope, A D; Traulsen, I; Schwarz, R; Granzer, T; Pires, A M; Thorstensen, J R

    2013-01-01

    V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as the optical counterpart of the bright, high-latitude ROSAT all-sky survey source RBS1955. The system was suspected to belong to a largely undiscovered population of hibernating CVs. Despite intensive optical follow-up its subclass however remained undetermined. We want to further classify V405 Peg and understand its role in the CV zoo via its long-term behaviour, spectral properties, energy distribution and accretion luminosity. We perform a spectral and timing analysis of \\textit{XMM-Newton} X-ray and ultra-violet data. Archival WISE, HST, and Swift observations are used to determine the spectral energy distribution and characterize the long-term variability. The X-ray spectrum is characterized by emission from a multi-temperature plasma. No evidence for a luminous soft X-ray component was found. Orbital phase-dependent X-ray photometric variability by $\\sim50\\%$ occurred without significant spectral changes. No further periodicity...

  20. Reversibility of time series: revealing the hidden messages in X-ray binaries and cataclysmic variables

    CERN Document Server

    Scaringi, S; Middleton, M

    2014-01-01

    We explore the non-linear, high-frequency, aperiodic variability properties in the three cataclysmic variables MV Lyr, KIC 8751494 and V1504 Cyg observed with Kepler, as well as the X-ray binary Cyg X-1 observed with RXTE. This is done through the use of a high-order Fourier statistic called the bispectrum and its related biphase and bicoherence, as well as the time-skewness statistic. We show how all objects display qualitatively similar biphase trends. In particular all biphase amplitudes are found to be smaller than $\\pi/2$, suggesting that the flux distributions for all sources are positively skewed on all observed timescales, consistent with the log-normal distributions expected from the fluctuating accretion disk model. We also find that for all objects the biphases are positive at frequencies where the corresponding power spectral densities display their high frequency break. This suggests that the noise-like flaring observed is rising more slowly than it is falling, and thus not time-reversible. This ...

  1. Disk Structure of Cataclysmic Variables in the light of Broadband Noise Characteristics

    Science.gov (United States)

    Balman, Solen

    2016-07-01

    Flicker noise and its variations in accreting systems have been a diagnostic tool in understanding the structure in accretion disks. I study the nature of time variability of brightness of non-magnetic cataclysmic variables. Dwarf novae demonstrate band limited noise in the UV and X-ray energy bands, which can be adequately explained in the framework of the model of propagating fluctuations. The detected frequency breaks in the range (1-6) mHz indicates an optically thick disk truncation in the inner disk of some dwarf novae systems. Analysis of other available data (SS Cyg, SU UMa, WZ Sge, Z Cha) indicate that during the outburst the inner disk radius moves towards the white dwarf and receeds as the outburst declines while changes in the X-ray energy spectrum is also observed. Cross-correlations between the simultaneous Optical, UV and X-ray light curves show time lags in the X-rays consistent with truncated inner optically thick disk. I compare magnetic and nonmagnetic CVs in terms of their broadband noise characteristics and summarize findings regarding broadband noise structure and time lags in other types of nonmagnetic CVs which in general show compliance with the model of propagating fluctuations. In addition, I discuss comparisons with X-ray binaries.

  2. An investigation of a magnetic cataclysmic variable with a period of 14.1 ks

    CERN Document Server

    Wang, Song; Zhang, Chuan-peng; Liu, Ji-feng

    2016-01-01

    Magnetic cataclysmic variables (CVs) contain a white dwarf with magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we discover a magnetic CV (CXOGSG J215544.4+380116) from the $Chandra$ archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source as a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2--M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass ($\\sim$ 0.4 $M_{\\odot}$) and radius ($\\sim$ 0.4 $R_{\\odot}$) for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/r...

  3. The Emergence of Negative Superhumps in Cataclysmic Variables: Smoothed Particle Hydrodynamics Simulations

    CERN Document Server

    Thomas, David M

    2016-01-01

    Negative superhumps are believed to arise in cataclysmic variable systems when the accretion disk is tilted with respect to the orbital plane. Slow retrograde precession of the line-of-nodes results in a signal---the negative superhump---with a period slightly less than the orbital period. Previous studies have shown that tilted disks exhibit negative superhumps, but a consensus on how a disk initially tilts has not been reached. Analytical work by Lai suggests that a magnetic field on the primary can lead to a tilt instability in a disk when the dipole moment is offset in angle from the spin axis of the primary and when the primary's spin axis is, itself, not aligned with the angular momentum axis of the binary orbit. However, Lai did not apply his work to the formation of negative superhumps. In this paper, we add Lai's model to an existing smoothed particle hydrodynamics code. Using this code, we demonstrate the emergence of negative superhumps in the "light curve" for a range of magnetic dipole moments. W...

  4. Photometry of the eclipsing cataclysmic variable SDSS J152419.33+220920.0

    CERN Document Server

    Michel, R; Hernandez-Santisteban, J V

    2013-01-01

    Aims. We present new photometry of the faint and poorly studied cataclysmic variable SDSS J152419.33+220920.0, analyze its light curve and provide an accurate ephemeris for this system. Methods. Time-resolved CCD differential photometry was carried out using the 1.5m and 0.84m telescopes at the Observatorio Astronomico Nacional at San Pedro Martir. Results. From time-resolved photometry of the system obtained during six nights (covering more than twenty primary eclipse cycles in more than three years), we show that this binary presents a strong primary and a weak secondary modulation. Our light curve analysis shows that only two fundamental frequencies are present, corresponding to the orbital period and a modulation with twice this frequency. We determine the accurate ephemeris of the system to be HJD(eclipse)= 2454967.6750(1) + 0.06531866661(1) E. A double-hump orbital period modulation, a standing feature in several bounce-back systems at quiescence, is present at several epochs. However, we found no other...

  5. Cataclysmic Variables from SDSS. VIII. The Final Year (2007-2008)

    CERN Document Server

    Szkody, Paula; Brooks, Keira; Gaensicke, Boris T; Kronberg, Martin; Riecken, Thomas; Ross, Nicholas P; Schmidt, Gary D; Schneider, Donald P; Agueros, Marcel A; Gomez-Moran, Ada N; Knapp, Gillian R; Schreiber, Matthias R; Schwope, Axel D

    2011-01-01

    This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey I/II. The coordinates, magnitudes and spectra of 33 CVs are presented. Among the 33 are eight systems known previous to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226 and HS0943+1404), as well as nine objects recently found through various photometric surveys. Among the systems identified since the SDSS are two polar candidates, two intermediate polar candidates and one candidate for containing a pulsating white dwarf. Our followup data have confirmed a polar candidate from Paper VII and determined tentative periods for three of the newly identified CVs. A complete summary table of the 285 CVs with spectra from SDSS I/II is presented as well as a link to an online table of all known CVs from both photometry and spectroscopy that will continue to be updated as future data appear.

  6. CATACLYSMIC VARIABLES FROM THE SLOAN DIGITAL SKY SURVEY. VIII. THE FINAL YEAR (2007-2008)

    Energy Technology Data Exchange (ETDEWEB)

    Szkody, Paula; Anderson, Scott F.; Brooks, Keira; Kronberg, Martin; Riecken, Thomas [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Gaensicke, Boris T. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Ross, Nicholas P. [Lawrence Berkeley National Lab, Berkeley, CA 92420 (United States); Schmidt, Gary D. [The University of Arizona, Steward Observatory, Tucson, AZ 85721 (United States); Schneider, Donald P. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Agueeros, Marcel A. [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Gomez-Moran, Ada N.; Schwope, Axel D. [Leibniz-Institut fuer Astrophysik Potsdam (AIP), 14482 Potsdam (Germany); Knapp, Gillian R. [Princeton University Observatory, Princeton, NJ 08544 (United States); Schreiber, Matthias R., E-mail: szkody@astro.washington.edu [Departamento de Fisica y Astronomia, Universidad de Valparaiso (Chile)

    2011-12-15

    This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey (SDSS) I/II. The coordinates, magnitudes, and spectra of 33 CVs are presented. Among the 33 are eight systems known prior to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226, and HS0943+1404), as well as nine objects recently found through various photometric surveys. Among the systems identified since the SDSS are two polar candidates, two intermediate polar candidates, and one candidate for containing a pulsating white dwarf. Our follow-up data have confirmed a polar candidate from Paper VII and determined tentative periods for three of the newly identified CVs. A complete summary table of the 285 CVs with spectra from SDSS I/II is presented as well as a link to an online table of all known CVs from both photometry and spectroscopy that will continue to be updated as future data appear.

  7. HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris

    CERN Document Server

    Knigge, C; Wade, R A; Baptista, R; Horne, K; Hubeny, I; Rutten, R G M

    1998-01-01

    [abridged abstract] 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 August of 1994 and with the PRISM (covering the near-ultraviolet to near-infrared) in November of the same year. The system was 50% brighter in November than in August, which, if due to a change in the accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%. Model disk spectra constructed as ensembles of stellar atmospheres provide poor descriptions of the observed post-eclipse 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_eff = 12,500-14,500 K actually provide a better match to both the ultraviolet and optical post-eclipse spectra. Evidently, great care must be taken in attempts to derive accretion rates fr...

  8. An Online Catalog of Cataclysmic Variable Spectra from the Far Ultraviolet Spectroscopic Explorer

    CERN Document Server

    Godon, P; Levay, K; Linnell, A P; Szkody, P; Barrett, P E; Hubeny, I; Blair, W P

    2012-01-01

    We present an online catalog containing spectra and supporting information for cataclysmic variables that have been observed with the Far Ultraviolet Spectroscopic Explorer (FUSE). For each object in the catalog we list some of the basic system parameters such as (RA,Dec), period, inclination, white dwarf mass, as well as information on the available FUSE spectra: data ID, observation date and time, and exposure time. In addition, we provide parameters needed for the analysis of the FUSE spectra such as the reddening E(B-V), distance, and state (high, low, intermediate) of the system at the time it was observed. For some of these spectra we have carried out model fits to the continuum with synthetic stellar and/or disk spectra using the codes TLUSTY and SYNSPEC. We provide the parameters obtained from these model fits; this includes the white dwarf temperature, gravity, projected rotational velocity and elemental abundances of C, Si, S and N, together with the disk mass accretion rate, the resulting inclinati...

  9. Mass transfer in cataclysmic variables - Clues from the dwarf nova period distribution

    Science.gov (United States)

    Shafter, A. W.; Wheeler, J. C.; Cannizzo, J. K.

    1986-01-01

    Evidence is presented in support of the hypothesis that the mean mass-transfer rate at a given orbital period is not continuous across the 2-3 hr gap in the orbital period distribution for cataclysmic variables. It is pointed out that although dwarf novae comprise nearly half (48 percent) of all disk systems with orbital periods less than 10 hr, only three systems out of the 22 with periods between 3 and 4 hr appear to be dwarf novae. The overall orbital period distribution for dwarf novae in conjunction with the predictions from current theories of dwarf nova eruptions are used to argue that mass-transfer rates must be generally higher for systems with orbital periods greater than 3 hr relative to systems with periods less than 2 hr. It is further argued that the mean mass-transfer rate at a given orbital period cannot increase more steeply than P exp 1.7 unless the white dwarf mass is positively correlated with orbital period.

  10. Population Synthesis of Cataclysmic Variables: I. Inclusion of Detailed Nuclear Evolution

    CERN Document Server

    Goliasch, J

    2016-01-01

    We have carried out an extensive population synthesis study of the ensemble properties of the present-day population of cataclysmic variables (PDCVs) that takes into account the nuclear evolution of high-mass donors close to the bifurcation and dynamical instability limits. Assuming the interrupted magnetic braking paradigm, we confirm many of the general features associated with the observed CV population and find enormous diversity in their secular properties. We predict that nearly half of the non-magnetic CVs with Porb > 6 hours are at least mildly evolved (i.e., greater than one-half of their MS turn-off age). Some of these systems contribute to the observed population of PDCVs in the period gap. We also see an enhancement by up to a factor of two in the probability of detecting CVs at the `minimum period'. This spike is quite narrow (approximately 5 minutes) and is attenuated because of the spectrum of WD masses and partly by the evolution of the donors. Our syntheses imply that there should be a very r...

  11. Doppler Tomography and Photometry of the Cataclysmic Variable 1RXS J064434.5+334451

    CERN Document Server

    Santisteban, J V Hernández; Michel, R; Costero, R

    2016-01-01

    We have obtained simultaneous photometric and spectroscopic observations of the cataclysmic variable 1RXS J064434.5+334451. We have calibrated the spectra for slit losses using the simultaneous photometry allowing to construct reliable Doppler images from H$\\alpha$ and HeII 4686 emission lines. We have improved the ephemeris of the object based on new photometric eclipse timings, obtaining $HJD = 2453403.759533 + 0.26937446E$. Some eclipses present a clear internal structure which we attribute to a central HeII emission region surrounding the white dwarf, a finding supported by the Doppler tomography. This indicates that the system has a large inclination angle $i=78 \\pm 2^{\\circ}$. We have also analysed the radial velocity curve from the emission lines to measure its semi--amplitude, $K_1$, from H$\\alpha$ and HeII 4686 and derive the masses of the components: $M_1=0.82\\pm0.06$ M$_{\\odot}$, $M_2=0.78\\pm0.04$ M$_{\\odot}$ and their separation $a=2.01\\pm0.06$ $R_{\\odot}$. The Doppler tomography and other observe...

  12. Radial velocity studies of HeII and Hβ emission from cataclysmic variables

    Science.gov (United States)

    Schwarz, C.; Montgomery, M. M.

    2014-02-01

    Radial velocity (RV) plots of HeII and Hβ emission lines from non-magnetic Cataclysmic Variable (CV) systems are frequently fit with a sin curve but sometimes contain outlying data points around phase ϕ∼1.0. A lack of consensus exists on the origin of these outlying points. In this work, we develop an analytical model that is based upon our 3D Smoothed Particle Hydrodynamic (SPH) numerical model to simulate these RV curves. Our chosen targets are CV SW Sextanis-like systems UX Uma and RW Tri as well as SU UMa dwarf novae systems Hα0242-28 and 1RXSJ1808+10, which have secondary-to-primary mass ratios of q = (0.43, 0.86, 0.27, 0.18), respectively. In our model, we include disk eccentricity, inclination angle, degree of disk-tilt, bright spot (s), and/or gas stream overflow. Our model provides good non-sinusoidal fits to the observed RV data, including outlying data points near ϕ∼1.0, suggesting these excess points may be caused by gas-stream overflow.

  13. THE ROLE OF WHITE DWARFS IN CATACLYSMIC VARIABLE SPIN-DOWN

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, O.; Drake, J. J.; Kashyap, V. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138 (United States)

    2012-02-10

    We study the effect of a white dwarf on the spin-down of a cataclysmic variable (CV) system using a three-dimensional magnetohydrodynamic numerical model. The model includes the stellar corona, the stellar wind, and the WD mass and magnetic field. The existence of the WD modifies the system spin-down by physically blocking the stellar wind, restructuring the wind, channeling the wind toward the WD surface, and modifying the shape and size of the Alfven surface. The combination of these processes differs among a set of simple test cases, and the resulting angular momentum loss rates vary by factors of 2-3, and by factors of 2 relative to a test model with a single M dwarf. While the model employs some simplifications, the results suggest that angular momentum loss schemes currently employed in CV studies do not require drastic revision. Insights are also gained on wind accretion. We find that efficient accretion switches on quite rapidly with decreasing orbital separation. Accretion rates depend on magnetic field alignment and should be modulated by magnetic cycles on the M dwarf. For particular values of white dwarf magnetic field strength, an efficient syphoning of coronal plasma from the inward facing M dwarf hemisphere occurs. Wind accretion rates are expected to vary by factors of 10 or more between fairly similar close binaries, depending on magnetic field strengths and orbital separation.

  14. UNAMBIGUOUS DETECTION OF REFLECTION IN MAGNETIC CATACLYSMIC VARIABLES: JOINT NuSTAR–XMM-NEWTON OBSERVATIONS OF THREE INTERMEDIATE POLARS

    Energy Technology Data Exchange (ETDEWEB)

    Mukai, K. [CRESST and X-ray Astrophysics Laboratory, NASA/GSFC, Greenbelt, MD 20771 (United States); Rana, V. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Bernardini, F. [New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi (United Arab Emirates); De Martino, D., E-mail: Koji.Mukai@nasa.gov [INAF—Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy)

    2015-07-10

    In magnetic cataclysmic variables (CVs), X-ray emission regions are located close to the white dwarf surface, which is expected to reflect a significant fraction of intrinsic X-rays above 10 keV, producing a Compton reflection hump. However, up to now, a secure detection of this effect in magnetic CVs has largely proved elusive because of the limited sensitivity of non-imaging X-ray detectors. Here we report our analysis of joint NuSTAR–XMM-Newton observations of three magnetic CVs, V709 Cas, NY Lup, and V1223 Sgr. The improved hard X-ray sensitivity of the imaging NuSTAR data has resulted in the first robust detection of Compton hump in all three objects, with amplitudes of ∼1 or greater in NY Lup, and likely <1.0 in the other two. We also confirm earlier reports of a strong spin modulation above 10 keV in V709 Cas, and we report the first detection of small spin amplitudes in the others. We interpret this as due to different height of the X-ray emitting region among these objects. A height of ∼0.2 white dwarf radii provides a plausible explanation for the low reflection amplitude of V709 Cas. Since emission regions above both poles are visible at certain spin phases, this can also explain the strong hard X-ray spin modulation. A shock height of ∼0.05 white dwarf radii can explain our results on V1223 Sgr, while the shock height in NY Lup appears negligible.

  15. 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.

  16. Effective temperatures of cataclysmic-variable white dwarfs as a probe of their evolution

    Science.gov (United States)

    Pala, A. F.; Gänsicke, B. T.; Townsley, D.; Boyd, D.; Cook, M. J.; De Martino, D.; Godon, P.; Haislip, J. B.; Henden, A. A.; Hubeny, I.; Ivarsen, K. M.; Kafka, S.; Knigge, C.; LaCluyze, A. P.; Long, K. S.; Marsh, T. R.; Monard, B.; Moore, J. P.; Myers, G.; Nelson, P.; Nogami, D.; Oksanen, A.; Pickard, R.; Poyner, G.; Reichart, D. E.; Rodriguez Perez, D.; Schreiber, M. R.; Shears, J.; Sion, E. M.; Stubbings, R.; Szkody, P.; Zorotovic, M.

    2017-04-01

    We present HST spectroscopy for 45 cataclysmic variables (CVs), observed with HST/COS and HST/STIS. For 36 CVs, the white dwarf is recognisable through its broad Ly α absorption profile and we measure the white dwarf effective temperatures (Teff) by fitting the HST data assuming log g = 8.35, which corresponds to the average mass for CV white dwarfs (≃0.8 M⊙). Our results nearly double the number of CV white dwarfs with an accurate temperature measurement. We find that CVs above the period gap have, on average, higher temperatures ( ≃ 23 000 K) and exhibit much more scatter compared to those below the gap ( ≃ 15 000 K). While this behaviour broadly agrees with theoretical predictions, some discrepancies are present: (i) all our new measurements above the gap are characterized by lower temperatures (Teff ≃ 16 000-26 000 K) than predicted by the present-day CV population models (Teff ≃ 38 000-43 000 K); (ii) our results below the gap are not clustered in the predicted narrow track and exhibit in particular a relatively large spread near the period minimum, which may point to some shortcomings in the CV evolutionary models. Finally, in the standard model of CV evolution, reaching the minimum period, CVs are expected to evolve back towards longer periods with mean accretion rates dot{M}≲ 2 × 10^{-11} M_{⊙} yr^{-1}, corresponding to Teff ≲ 11 500 K. We do not unambiguously identify any such system in our survey, suggesting that this major component of the predicted CV population still remains elusive to observations.

  17. MyNewsFlash: A System for Near Real-Time Variable Star Monitoring and Alerts

    Science.gov (United States)

    Price, A.; Turner, R.; Malatesta, K.; Simonsen, M. A.

    2004-12-01

    MyNewsFlash is an automated and customizable system for distributing timely variable star data. It supplies near real-time reports to the user of the latest activity of a variable star or class of stars. The stars it monitors, the frequency of report delivery, the delivery format, and more features are all completely customizable so the reader receives only reports of information he or she wants and nothing more or less. In addition, manually-generated alerts called Special MyNewsFlashes are occasionally sent out with additional information on special or abnormal behavior of a variable star. MyNewsFlash evolved from the AAVSO News Flash, an electronic publication dedicated to outbursts of popular cataclysmic variable stars

  18. Automated Searches for Variable Stars

    CERN Document Server

    Van Noord, Daniel M; Steenwyk, Steven D

    2013-01-01

    With recent developments in imaging and computer technology the amount of available astronomical data has increased dramatically. Although most of these data sets are not dedicated to the study of variable stars much of it can, with the application of proper software tools, be recycled for the discovery of new variable stars. Fits Viewer and Data Retrieval System is a new software package that takes advantage of modern computer advances to search astronomical data for new variable stars. More than 200 new variable stars have been found in a data set taken with the Calvin College Rehoboth Robotic telescope using FVDRS. One particularly interesting example is a very fast subdwarf B with a 95 minute orbital period, the fastest currently known of the HW Vir type.

  19. Variable stars in the classroom

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Bajo, F [Departamento de Electronica e IngenierIa Electromecanica, Escuela de IngenierIas Industriales, Universidad de Extremadura, Avda de Elvas s/n, 06071 Badajoz (Spain); Vaquero, J M [Departamento de Fisica, Escuela Politecnica, Universidad de Extremadura, Avda de la Universidad s/n, 10071 Caceres (Spain)

    2006-05-01

    Variable stars offer interesting possibilities from the point of view of educational applications, from the experimental collection of data to analysis to obtain physical information. In this paper, brightness measurements of two periodic variable stars easily accessible with small telescopes are presented and analysed. This practical experiment is highly appropriate for educational use in undergraduate physics and astrophysics laboratories and allows students to approximate scientific research.

  20. The space density and X-ray luminosity function of non-magnetic cataclysmic variables

    Science.gov (United States)

    Pretorius, Magaretha L.; Knigge, Christian

    2012-01-01

    We combine two complete, X-ray flux-limited surveys, the ROSAT Bright Survey (RBS) and the ROSAT North Ecliptic Pole (NEP) survey, to measure the space density (ρ) and X-ray luminosity function (Φ) of non-magnetic cataclysmic variables (CVs). The combined survey has a flux limit of FX≳ 1.1 × 10-12 erg cm-2 s-1 over most of its solid angle of just over ?, but is as deep as ≃10-14 erg cm-2 s-1 over a small area. The CV sample that we construct from these two surveys contains 20 non-magnetic systems. We carefully include all sources of statistical error in calculating ρ and Φ by using Monte Carlo simulations; the most important uncertainty proves to be the often large errors in distances estimates. If we assume that the 20 CVs in the combined RBS and NEP survey sample are representative of the intrinsic population, the space density of non-magnetic CVs is ?. We discuss the difficulty in measuring Φ in some detail - in order to account for biases in the measurement, we have to adopt a functional form for Φ. Assuming that the X-ray luminosity function of non-magnetic CVs is a truncated power law, we constrain the power-law index to -0.80 ± 0.05. It seems likely that the two surveys have failed to detect a large, faint population of short-period CVs, and that the true space density may well be a factor of 2 or 3 larger than what we have measured; this is possible, even if we only allow for undetected CVs to have X-ray luminosities in the narrow range 28.7 log(LX/erg s-1) < 29.7. However, ρ as high as 2 × 10-4 pc-3 would require that the majority of CVs has X-ray luminosities below LX= 4 × 1028 erg s-1 in the 0.5-2.0 keV band.

  1. 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

  2. VizieR Online Data Catalog: Radial velocities of 35 cataclysmic variables (Thorstensen+, 2016)

    Science.gov (United States)

    Thorstensen, J. R.; Alper, E. H.; Weil, K. E.

    2017-02-01

    We present spectroscopic follow-up observations of 35 newly discovered cataclysmic variables (CVs), 32 of which were found by the Catalina Real Time Transient Surveys (CRTS; Drake et al. 2009, Cat. J/ApJ/696/870; Drake et al. 2014, Cat. J/MNRAS/441/1186; Breedt et al. 2014, Cat. J/MNRAS/443/3174), ASAS-SN (Shappee et al. 2014ApJ...788...48S), and/or MASTER (Lipunov et al. 2010AdAst2010E..30L). All our observations are from Michigan-Dartmouth-MIT (MDM) Observatory on Kitt Peak, Arizona. For nearly all the spectra, we used the "modspec" spectrograph (a description of the modspec can be found at http://mdm.kpno.noao.edu/Manuals/ModSpec/modspec_man.html) with a 600line/mm grating. We mostly used a SITe 20482 CCD detector, which yielded 2Å/pixel from 4210 to 7500Å, with declining throughput toward the ends of the spectral range. When this detector was unavailable, we used a very similar 10242 SITe detector ("Templeton"), which covered 4660 to 6730Å. The modspec was mounted mostly on the 2.4m Hiltner telescope, but for some of the brighter objects, we used the 1.3m McGraw-Hill telescope. For a few of the 1.3m spectra, we used the Mark III grism spectrograph, which covered 4580 to 6850Å at 2.3Å/pixel. On both telescopes and with both spectrographs, we used an Andor Ikon camera to view the reflective slit jaws through a microscope and guided the telescope with a separate off-axis guider. With this arrangement we could place any object that was bright enough for a usable spectrum in the slit and track it accurately even if the portion of the light spilling onto the slit jaws was invisible. Our emission-line radial velocities are almost entirely of Hα, since it almost always gives the best signal-to-noise ratio with our instrument. (3 data files).

  3. Anomalous ultraviolet line flux ratios in the cataclysmic variables 1RXSJ232953.9+062814, CE315, BZ UMa and EY Cyg observed with HST/STIS

    CERN Document Server

    Gänsicke, B T; De Martino, D; Beuermann, K; Long, K S; Sion, E M; Knigge, C; Marsh, T; Hubeny, I; G\\"ansicke, Boris T.; Szkody, Paula; Martino, Domitilla de; Beuermann, Klaus; Long, Knox S.; Sion, Edward M.; Knigge, Christian; Marsh, Tom; Hubeny, Ivan

    2003-01-01

    Brief HST/STIS spectroscopic snapshot exposures of the cataclysmic variables 1RXSJ232953.9+062814, CE315, BZ UMa and EY Cyg reveal very large NV/CIV line flux ratios, similar to those observed in AE Aqr. Such anomalous line flux ratios have so far been observed in 10 systems, and presumably reflect a different composition of the accreted material compared to the majority of cataclysmic variables. We discuss the properties of this small sample in the context of the recent proposal by Schenker et al. (2002) that a significant fraction of the present-day population of cataclysmic variables may have passed through a phase of thermal time-scale mass transfer.

  4. New Close Binary Systems from the SDSS-I (Data Release Five) and the Search for Magnetic White Dwarfs in Cataclysmic Variable Progenitor Systems

    CERN Document Server

    Silvestri, Nicole M; Hawley, Suzanne L; West, Andrew A; Schmidt, Gary D; Liebert, James; Szkody, Paula; Mannikko, Lee; Wolfe, Michael A; Barentine, J C; Brewington, Howard J; Harvanek, Michael; Krzesinski, Jurik; Long, Dan; Schneider, Donald P; Snedden, Stephanie A

    2007-01-01

    We present the latest catalog of more than 1200 spectroscopically-selected close binary systems observed with the Sloan Digital Sky Survey through Data Release Five. We use the catalog to search for magnetic white dwarfs in cataclysmic variable progenitor systems. Given that approximately 25% of cataclysmic variables contain a magnetic white dwarf, and that our large sample of close binary systems should contain many progenitors of cataclysmic variables, it is quite surprising that we find only two potential magnetic white dwarfs in this sample. The candidate magnetic white dwarfs, if confirmed, would possess relatively low magnetic field strengths (B_WD < 10 MG) that are similar to those of intermediate-Polars but are much less than the average field strength of the current Polar population. Additional observations of these systems are required to definitively cast the white dwarfs as magnetic. Even if these two systems prove to be the first evidence of detached magnetic white dwarf + M dwarf binaries, th...

  5. Cataclysmic Variables and Other Compact Binaries in the Globular Cluster NGC 362: Candidates from Chandra and HST

    CERN Document Server

    Margon, Bruce; Homer, L; Pooley, D; Bassa, C G; Anderson, S F; Lewin, W H G; Verbunt, F; Kong, A K H; Plotkin, R M

    2010-01-01

    Highly sensitive and precise X-ray imaging from Chandra, combined with the superb spatial resolution of HST optical images, dramatically enhances our empirical understanding of compact binaries such as cataclysmic variables and low mass X-ray binaries, their progeny, and other stellar X-ray source populations deep into the cores of globular clusters. Our Chandra X-ray images of the globular cluster NGC 362 reveal 100 X-ray sources, the bulk of which are likely cluster members. Using HST color-magnitude and color-color diagrams, we quantitatively consider the optical content of the NGC 362 Chandra X-ray error circles, especially to assess and identify the compact binary population in this condensed-core globular cluster. Despite residual significant crowding in both X-rays and optical, we identify an excess population of H{\\alpha}-emitting objects that is statistically associated with the Chandra X-ray sources. The X-ray and optical characteristics suggest that these are mainly cataclysmic variables, but we al...

  6. HS0139+0559, HS0229+8016, HS0506+7725 and HS0642+5049: Four new long-period cataclysmic variables

    CERN Document Server

    Aungwerojwit, A; Rodríguez-Gil, P; Hagen, H J; Harlaftis, E T; Papadimitriou, C; Lehto, H; Araújo-Betancor, S; Heber, U; Fried, R E; Engels, D; Katajainen, S

    2005-01-01

    We present time-resolved optical spectroscopy and photometry of four relatively bright (V~14.0-15.5) long-period cataclysmic variables (CVs) discovered in the Hamburg Quasar Survey: HS0139+0559, HS0229+8016, HS0506+7725 and HS0642+5049. Their respective orbital periods, 243.69+-0.49min, 232.550+-0.049min, 212.7+-0.2min and 225.90+-0.23min are determined from radial velocity and photometric variability studies. HS0506+7725 is characterised by strong Balmer and He emission lines, short-period (~10-20min) flickering and weak X-ray emission in the ROSAT All Sky Survey. The detection of a deep low state (~18.5) identifies HS0506+7725 as a member of the VY Scl stars. HS0139+0559, HS0229+8016 and HS0642+5049 display thick-disc like spectra and no or only weak flickering activity. HS0139+0559 and HS0229+8016 exhibit clean quasi-sinusoidal radial velocity varations of their emission lines but no or very little orbital photometric variability. In contrast, we detect no radial velocity variation in HS0642+5049 but a not...

  7. Time resolved spectroscopy and photometry of three little known bright cataclysmic variables: LS IV -08$^{\\rm o}$ 3, HQ Monocerotis and ST Chamaeleontis

    CERN Document Server

    Bruch, Albert

    2016-01-01

    As part of a project to better characterize comparatively bright but so far little studied cataclysmic variables in the southern hemisphere, we have obtained spectroscopic and photometric data of the nova-like variables LS IV -08$^{\\rm o}$ 3 and HQ Mon, and of the Z Cam type dwarf nova ST Cha. The spectra of all systems are as expected for their respective types. We derive improved orbital ephemeris of LS IV -08$^{\\rm o}$ 3 and map its accretion disk in the light of the H$\\alpha$ emission using Doppler tomography. We find that the emission has a two component origin, arising in the outer parts of the accretion disk and possibly on the illuminated face of the secondary star. The light curve of LS IV -08$^{\\rm o}$ 3 exhibits a low level of flickering and indications for a modulation on the orbital period. Spectroscopy of HQ Mon suggests an orbital period of $\\approx$5.15 hours which is incompatible with previous (uncertain) estimates. The light curves show the typical low scale flickering of UX UMa type nova-li...

  8. Multi-band study of a new asynchronous magnetic cataclysmic variable and a flaring X-ray source

    CERN Document Server

    Rea, N; Esposito, P; D'Avanzo, P; de Martino, D; Israel, G L; Torres, D F; Campana, S; Belloni, T M; Papitto, A; Masetti, N; Carrasco, L; Possenti, A; Wieringa, M; Wilhelmi, E De Ona; Li, J; Bozzo, E; Ferrigno, C; Linares, M; Tauris, T M; Hernanz, M; Ribas, I; Monelli, M; Borghese, A; Baglio, M C; Casares, J

    2016-01-01

    In search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we report on 1) a new magnetic Cataclysmic Variable (mCV), RX J0838-2827, that we identify as an asynchronous system (therefore not associated with this Fermi-LAT source) and 2) on a new X-ray flaring source, XMM J083850.4-282759, that might be tentatively identified as new candidate Transitional Millisecond Pulsar, possibly associated with the gamma-ray source. We observed the field in the X-ray band with Swift, twice with XMM-Newton, as well as performed infrared, optical (with OAGH, ESO-NTT and IAC80) and radio (ATCA) observations, and we report on archival INTEGRAL observations. RX J0838-2827 is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as due to the binary system orbital period of ~1.64hr and the white dwarf spin period of ~1.47hr. Furthermore, a strong flux modulation at ...

  9. Time resolved spectroscopy and photometry of three little known bright cataclysmic variables: LS IV -08° 3, HQ Monocerotis and ST Chamaeleontis

    Science.gov (United States)

    Bruch, Albert; Diaz, Marcos P.

    2017-01-01

    As part of a project to better characterize comparatively bright but so far little studied cataclysmic variables in the southern hemisphere, we have obtained spectroscopic and photometric data of the nova-like variables LS IV -08° 3 and HQ Mon, and of the Z Cam type dwarf nova ST Cha. The spectra of all systems are as expected for their respective types. We derive improved orbital ephemeris of LS IV -08° 3 and map its accretion disk in the light of the Hα emission using Doppler tomography. We find that the emission has a two component origin, arising in the outer parts of the accretion disk and possibly on the illuminated face of the secondary star. The light curve of LS IV -08° 3 exhibits a low level of flickering and indications for a modulation on the orbital period. Spectroscopy of HQ Mon suggests an orbital period of ≈ 5h.15 which is incompatible with previous (uncertain) estimates. The light curves show the typical low scale flickering of UX UMa type nova-like systems, superposed upon variations on longer time scales. During one night a modulation with a period of ≈ 41m is observed, visible for at least 4 hours. However, it does not repeat itself in other nights. A spectroscopic orbital period of ≈ 5h.5 is derived for ST Cha. A previously suspected period of 6h.8 (or alternatively 9h.6), based on historical photographic photometry is incompatible with the spectroscopic period. Moreover, we show that our new as well as previous photometry does not contain evidence for the quoted photometric period.

  10. On the evolution of accretion disc flow in cataclysmic variables. III - Outburst properties of constant and uniform-alpha model discs

    Science.gov (United States)

    Lin, D. N. C.; Faulkner, J.; Papaloizou, J.

    1985-01-01

    Attention is given to the stability and evolution of some simple accretion disk models in which the viscosity is prescribed by an ad hoc, uniform-alpha model. Emphasis is placed on systems in which the mass input rate from the secondary to the disk around the primary is assumed to be constant, although initial calculations with variable mass input rates are also performed. Time-dependent visual magnitude light curves constructed for cataclysmic binaries with a range of disk size, primary mass and mass input rate, and viscosity magnitude, are compared with the observed properties of various cataclysmic variable subclasses. The results obtained indicate that the observational differences between novae and dwarf novae may be due to mass input rate differences. The present models can reproduce the gross observational features of U-Gem-type dwarf nova outbursts.

  11. Supervised Ensemble Classification of Kepler Variable Stars

    CERN Document Server

    Bass, Gideon

    2016-01-01

    Variable star analysis and classification is an important task in the understanding of stellar features and processes. While historically classifications have been done manually by highly skilled experts, the recent and rapid expansion in the quantity and quality of data has demanded new techniques, most notably automatic classification through supervised machine learning. We present an expansion of existing work on the field by analyzing variable stars in the {\\em Kepler} field using an ensemble approach, combining multiple characterization and classification techniques to produce improved classification rates. Classifications for each of the roughly 150,000 stars observed by {\\em Kepler} are produced separating the stars into one of 14 variable star classes.

  12. SWIFT XRT Observations of the Nova-like Cataclysmic Variables MV Lyr, BZ Cam and V592 Cas

    CERN Document Server

    Balman, Solen; Sion, Edward M

    2014-01-01

    We present a total of ~ 45 ksec (3$\\times$15 ksec) of SWIFT XRT observations for three non-magnetic nova-like (NL) Cataclysmic Variables (CVs) (MV Lyr, BZ Cam, V592 Cas) in order to study characteristics of Boundary Layers (BL) in CVs. The nonmagnetic NLs are found mostly in a state of high mass accretion rate ($\\ge$1$\\times$10$^{-9}$ Msun yr$^{-1}$) and some show occasional low states. Using the XRT data, we find optically thin multiple-temperature cooling flow type emission spectra with X-ray temperatures (kT$_{max}$) of 21-50 keV. These hard X-ray emitting boundary layers diverge from simple isobaric cooling flows indicating X-ray temperatures that are of virial values in the disk. In addition, we detect power law emission components from MV Lyr and BZ Cam and plausibly from V592 Cas which may be a result of the Compton scattering of the optically thin emission from the fast wind outflows in these systems and/or Compton up-scattering of the soft disk photons. The X-ray luminosities of the (multi-temperatur...

  13. Accretion and Outflow in Interacting Binary Systems FUSE Observations of the Novalike Cataclysmic Variable, UX Ursae Majoris

    CERN Document Server

    Froning, C S; Knigge, C

    2003-01-01

    We present far-ultraviolet (905 -- 1182 A), time-series spectroscopy of the eclipsing, novalike cataclysmic variable, UX UMa, acquired with FUSE. The time-averaged spectrum is complex and is dominated by overlapping spectral features. The most prominent features are emission lines of CIII, NIII}, NIV, and OVI. They are broad (FWHM >= 1800 km/s) and double-peaked with a central absorption at zero velocity. During eclipse, the spectrum is simpler: the emission lines remain bright, but the absorption components of the lines and the weaker features between the emission lines disappear entirely, leaving a flat continuum. This behavior is also evident in GHRS (1149 -- 1660 A) spectra that we retrieved from the HST archive. The FUV spectra show flickering on time scales of several minutes. The flickering is seen primarily in the continuum and/or the weaker lines rather than in the prominent emission lines. The orbital light curve has a dip in the FUV flux between orbital phases 0.45 -- 0.65, similar to a pre-eclipse...

  14. 1RXSJ173021.5-055933: a cataclysmic variable with a fast-spinning magnetic white dwarf

    CERN Document Server

    De Martino, D; Mukai, K; Bonnet-Bidaud, J -M; Falanga, M; Gänsicke, B T; Haberl, F; Marsh, T R; Mouchet, M; Littlefair, S P; Dhillon, V

    2008-01-01

    We present the first X-ray observations with the XMM-Newton and INTEGRAL satellites of the recently discovered cataclysmic variable 1RXSJ173021.5-055933, together with simultaneous UV and coordinated optical photometry aiming at characterising its broad-band temporal and spectral properties and classifying this system as a magnetic one. We find that the X-ray light curve is dominated by the 128s spin period of the accreting white dwarf in contrast to the far-UV range, which turns out to be unmodulated at a 3sigma level. Near-UV and optical pulses are instead detected at twice the spin frequency. We identify the contributions from two accreting poles that imply a moderately inclined dipole field allowing, one pole to dominate at energies at least up to 10keV, and a secondary that instead is negligible above 5keV. X-ray spectral analysis reveals the presence of multiple emission components consisting of optically thin plasma with temperatures ranging from 0.17keV to 60keV and a hot blackbody at ~90eV. The spect...

  15. Recovery of 29 s Oscillations in HST/FOS Eclipse Observations of the Cataclysmic Variable UX Ursae Majoris

    CERN Document Server

    Knigge, C; Long, K S; Wade, R A; Horne, K; Baptista, R

    1998-01-01

    [abridged abstract] Low amplitude (~=0.5%) 29-s oscillations have been detected in HST/FOS 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 by Warner & Nather in 1972. The oscillations are sinusoidal to within the small observational errors and undergo an approximately -360 degree phase shift during eclipses. Their amplitudes are highest at pre-eclipse orbital phases and exhibit a rather gradual eclipse whose shape is roughly similar to UX~UMa's overall light curve. Oscillation spectra derived from pre-eclipse data segments are extremely blue, whereas mid-eclipse oscillation spectra are much redder. We suggest that the ultimate source of the oscillations is a hot, compact region near disk center, but that a significant fraction of the observed, modulated flux is due to reprocessing of the light emitted by this source in the accretion disk atmosphere. The compact source is occulted at orbital ph...

  16. Optical Identification of Multiple Faint X-ray Sources in the Globular Cluster NGC 6752 Evidence for Numerous Cataclysmic Variables

    CERN Document Server

    Pooley, D; Homer, L; Verbunt, F; Anderson, S F; Gaensler, B M; Margon, B; Miller, J; Fox, D W; Kaspi, V M; Van der Klis, M

    2002-01-01

    We report on the Chandra ACIS-S3 imaging observation of the globular cluster NGC 6752. We detect 6 X-ray sources within the 10.5" core radius and 13 more within the 115" half-mass radius down to a limiting luminosity of Lx approx 10^{30} erg/s for cluster sources. We reanalyze archival data from the Hubble Space Telescope and the Australia Telescope Compact Array and make 12 optical identifications and one radio identification. Based on X-ray and optical properties of the identifications, we find 10 likely cataclysmic variables (CVs), 1-3 likely RS CVn or BY Dra systems, and 1 or 2 possible background objects. Of the 7 sources for which no optical identifications were made, we expect that ~2-4 are background objects and that the rest are either CVs or some or all of the 5 millisecond pulsars whose radio positions are not yet accurately known. These and other Chandra results on globular clusters indicate that the dozens of CVs per cluster expected by theoretical arguments are finally being found. The findings ...

  17. The Classificiation of Kepler B star Variables

    CERN Document Server

    McNamara, Bernard J; McKeever, Jean

    2012-01-01

    The light curves of 252 B-star candidates in the Kepler data base are analyzed in a similar fashion to that done by Balona et al. (2011) 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, $\\beta$ Cep stars, slowly pulsating B stars, 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 contants 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 data base by Balona et al. (2011) in the following fashion: $\\beta$ Cep stars from 0 to 10, slowly pulsating B stars from 8 to 54, hybrid pulsators from 7 to 21, and Bin/Rot stars from 23 to 82. For comparison purposes, approximately 51 SPBs and 6 hy...

  18. Meta Classification for Variable Stars

    CERN Document Server

    Pichara, Karim; León, Daniel

    2016-01-01

    The need for the development of automatic tools to explore astronomical databases has been recognized since the inception of CCDs and modern computers. Astronomers already have developed solutions to tackle several science problems, such as automatic classification of stellar objects, outlier detection, and globular clusters identification, among others. New science problems emerge and it is critical to be able to re-use the models learned before, without rebuilding everything from the beginning when the science problem changes. In this paper, we propose a new meta-model that automatically integrates existing classification models of variable stars. The proposed meta-model incorporates existing models that are trained in a different context, answering different questions and using different representations of data. Conventional mixture of experts algorithms in machine learning literature can not be used since each expert (model) uses different inputs. We also consider computational complexity of the model by ...

  19. Discovery of Four Peculiar Variable Stars

    Institute of Scientific and Technical Information of China (English)

    Xiao-Bin Zhang; Rong-Xian Zhang

    2003-01-01

    Four stars, GSC 1258-0143, GSC 1986-1665, GSC 3045-0892 and GSC2983-1597 were found to be new variables during a campaign of CCD photometricmonitoring of short-period eclipsing binary stars. The variabilities of these newvariables are reported. The main characteristics and probable classifications of thevariables are discussed through a preliminary analysis on their light curves. Amongthese stars, GSC 1258-0143 is classified as a RR Lyr star of sub-type a. Its pulsationperiod is determined to be about 0.5206 days. The other three stars, are definitevariables, but their periods and types of light variations remain unknown.

  20. Variable stars in the field of the open cluster NGC 7789

    CERN Document Server

    Mochejska, B J

    1999-01-01

    We present the results of our search for variable stars in the intermediate-age open cluster NGC 7789. We have found 45 variable stars: 35 eclipsing binaries, five pulsating variables and five miscellaneous variables. Most of the eclipsing binaries show W UMa type of variability, with periods shorter than one day. Four systems exhibit unusual behavior: two, V4276 and V6698, are probably RS CVn stars, another, V3283, is a possible cataclysmic binary. The nature of the fourth binary, V2130, is unclear: the system exhibits assymetric maxima. Among the pulsating variables two, V3407C and V4805 are background RR Lyrae stars and one, V6736, is a delta Scuti variable which is a blue straggler belonging to the cluster. Some of the miscellaneous variables may have periods longer than the five day timespan of our observations. We also present a color-magnitude diagram for the NGC 7789 open cluster, fairly complete down to V ~ 20. The relatively large number of variables found in the comparison field (14 compared to 31 ...

  1. Search for Variable Stars and Their Study

    Science.gov (United States)

    Kokumbaeva, R. I.; Zakhozhay, V. A.; Khruslov, A. V.

    We search for variable stars and study them using our CCD observations, observations available in the CSS, NSVS, ASAS-3 and Super-WASP online public archives.Our CCD observations were performed using the Zeiss- 1000 telescope of the V.G. Fesenkov Astrophysical Institute's Tien-Shan Astronomical Observatory. Earlier, as a result of our search using CCD images, we detected 27 new variable stars; using the NSVS and SuperWASP databases, we detected 12 new red semiregular and irregular variable stars.In this paper, we present our study of seven known variables based on the ASAS-3 and SuperWASP databases. All these stars remained poorly studied, their light elements were unknown, variability types were considered preliminary only. We studied two eclipsing variables (FY And and V2250 Sgr) and five Mira-stars (BZ Sco, CZ Sco, FK Sco, V880 Sco and V1818 Sgr).

  2. V344 Lyrae: A Touchstone SU UMa Cataclysmic Variable in the Kepler Field

    OpenAIRE

    2011-01-01

    We report on the analysis of the Kepler short-cadence (SC) light curve of V344 Lyr obtained during 2009 June 20 through 2010 Mar 19 (Q2--Q4). The system is an SU UMa star showing dwarf nova outbursts and superoutbursts, and promises to be a touchstone for CV studies for the foreseeable future. The system displays both positive and negative superhumps with periods of 2.20 and 2.06-hr, respectively, and we identify an orbital period of 2.11-hr. The positive superhumps have a maximum amplitude o...

  3. A Low-Resolution Spectroscopic Exploration of Puzzling OGLE Variable Stars

    CERN Document Server

    Pietrukowicz, P; Angeloni, R; di Mille, F; Soszynski, I; Udalski, A; Germana, C

    2015-01-01

    We present the results of a spectroscopic follow-up of various puzzling variable objects detected in the OGLE-III Galactic disk and bulge fields. The sample includes mainly short-period multi-mode pulsating stars that could not have been unambiguously classified as either delta Sct or beta Cep type stars based on photometric data only, also stars with irregular fluctuations mimicking cataclysmic variables and stars with dusty shells, and periodic variables displaying brightenings in their light curves that last for more than half of the period. The obtained low-resolution spectra show that all observed short-period pulsators are of delta Sct type, the stars with irregular fluctuations are young stellar objects, and the objects with regular brightenings are A type stars or very likely Ap stars with strong magnetic field responsible for the presence of bright caps around magnetic poles on their surface. We also took spectra of objects designated OGLE-GD-DSCT-0058 and OGLE-GD-CEP-0013. An estimated effective tem...

  4. Variable Star Astronomy Education & Public Outreach Initiative

    Science.gov (United States)

    Young, Donna L.

    2008-05-01

    The American Association of Variable Star Observers (AAVSO) published a comprehensive variable star curriculum, "Hands-On Astrophysics, Variable Stars in Science, Math, and Computer Education" in 1997. The curriculum, funded by the National Science Foundation, was developed for a comprehensive audience -- amateur astronomers, classroom educators, science fair projects, astronomy clubs, family learning, and anyone interested in learning about variable stars. Some of the activities from the Hands-On Astrophysics curriculum have been incorporated into the educational materials for the Chandra X-Ray Observatory's Educational and Public Outreach (EPO) Office. On two occasions, in 2000 and 2001, triggered by alerts from amateur astronomers, Chandra observed the outburst of the dwarf nova SS Cygni. The cooperation of amateur variable star astronomers and Chandra X-Ray scientists provided proof that the collaboration of amateur and professional astronomers is a powerful tool to study cosmic phenomena. Once again, the Chandra and AAVSO have teamed up -- this time to promote variable star education. The Hands-On Astrophysics curriculum is being re-designed and updated from the original materials to a web-based format. The new version, re-named Variable Star Astronomy, will provide formal and informal educators, and especially amateur astronomers, educational materials to help promote interest in and knowledge of variable stars.

  5. The implications of disc instabilities on cataclysmic Variable structure and evolution

    Directory of Open Access Journals (Sweden)

    J. P. Lasota

    2004-01-01

    Full Text Available Al aplicar el modelo de inestabilidad t ermico-viscosa del disco a varias clases de variables catacl smicas, con frecuencia se requiere que el disco de acreci on sea truncado. Arguyo que en la mayor a de los casos este truncamiento interno se debe al campo magn etico de la enana blanca.

  6. Spitzer Space Telescope observations of magnetic cataclysmic variables: possibilities for the presence of dust in polars

    CERN Document Server

    Brinkworth, C S; Wachter, S; Howell, S B; Ciardi, D R; Szkody, P; Harrison, T E; van Belle, G T; Esin, A A; 10.1086/512797

    2009-01-01

    We present Spitzer Space Telescope photometry of six short-period polars, EF Eri, V347 Pav, VV Pup, V834 Cen, GG Leo, and MR Ser. We have combined the Spitzer Infrared Array Camera (3.6 -8.0 microns) data with the 2MASS J, H, K_s photometry to construct the spectral energy distributions of these systems from the near- to mid-IR (1.235 - 8 microns). We find that five out of the six polars have flux densities in the mid-IR that are substantially in excess of the values expected from the stellar components alone. We have modeled the observed SEDs with a combination of contributions from the white dwarf, secondary star, and either cyclotron emission or a cool, circumbinary dust disk to fill in the long-wavelength excess. We find that a circumbinary dust disk is the most likely cause of the 8 micron excess in all cases, but we have been unable to rule out the specific (but unlikely) case of completely optically thin cyclotron emission as the source of the observed 8 micron flux density. While both model components...

  7. Interstellar Absorption Lines in the Direction of the Cataclysmic Variable SS Cygni

    CERN Document Server

    Ritchey, Adam M; McKeever, Jean

    2013-01-01

    We present an analysis of interstellar absorption lines in high-resolution optical echelle spectra of SS Cyg obtained during an outburst in 2013 June and in archival Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer data. The Ca II K and Na I D lines toward SS Cyg are compared with those toward nearby B and A stars in an effort to place constraints on the distance to SS Cyg. We find that the distance constraints are not very robust from this method due to the rather slow increase in neutral gas column density with distance and the scatter in the column densities from one sight line to another. However, the optical absorption-line measurements allow us to derive a precise estimate for the line-of-sight reddening of E(B-V) = 0.020+/-0.005 mag. Furthermore, our analysis of the absorption lines of O I, Si II, P II, and Fe II seen in the UV spectra yields an estimate of the H I column density and depletion strength in this direction.

  8. V344 Lyrae: A Touchstone SU UMa Cataclysmic Variable in the Kepler Field

    CERN Document Server

    Wood, Matt A; Howell, Steve B; Cannizzo, John K; Smale, Alan P

    2011-01-01

    We report on the analysis of the Kepler short-cadence (SC) light curve of V344 Lyr obtained during 2009 June 20 through 2010 Mar 19 (Q2--Q4). The system is an SU UMa star showing dwarf nova outbursts and superoutbursts, and promises to be a touchstone for CV studies for the foreseeable future. The system displays both positive and negative superhumps with periods of 2.20 and 2.06-hr, respectively, and we identify an orbital period of 2.11-hr. The positive superhumps have a maximum amplitude of ~0.25-mag, the negative superhumps a maximum amplitude of ~0.8 mag, and the orbital period at quiescence has an amplitude of ~0.025 mag. The quality of the Kepler data is such that we can test vigorously the models for accretion disk dynamics that have been emerging in the past several years. The SC data for V344 Lyr are consistent with the model that two physical sources yield positive superhumps: early in the superoutburst, the superhump signal is generated by viscous dissipation within the periodically flexing disk, ...

  9. Kepler Observations of V447 Lyr: An Eclipsing U Gem Cataclysmic Variable

    CERN Document Server

    Ramsay, Gavin; Howell, Steve B; Wood, Matt A; Still, Martin; Barclay, Thomas; Smale, Alan

    2012-01-01

    We present the results of an analysis of data covering 1.5 years of the dwarf nova V447 Lyr. We detect eclipses of the accretion disk by the mass donating secondary star every 3.74 hrs which is the binary orbital period. V447 Lyr is therefore the first dwarf nova in the Kepler field to show eclipses. We also detect five long outbursts and six short outbursts showing V447 Lyr is a U Gem type dwarf nova. We show that the orbital phase of the mid-eclipse occurs earlier during outbursts compared to quiescence and that the width of the eclipse is greater during outburst. This suggests that the bright spot is more prominent during quiescence and that the disk is larger during outburst than quiescence. This is consistent with an expansion of the outer disk radius due to the presence of high viscosity material associated with the outburst, followed by a contraction in quiescence due to the accretion of low angular momentum material. We note that the long outbursts appear to be triggered by a short outburst, which is ...

  10. Fe Line Diagnostics of Cataclysmic Variables and Galactic Ridge X-ray Emission

    CERN Document Server

    Xu, Xiao-jie; Li, Xiang-Dong

    2016-01-01

    The properties of the Galactic Ridge X-ray Emission (GRXE) observed in the 2-10 keV band place fundamental constraints on various types of X-ray sources in the Milky Way. Although the primarily discrete origin of the emission is now well established, the responsible populations of these sources remain uncertain, especially at relatively low fluxes. To provide insights into this issue, we systematically characterize the Fe emission line properties of the candidate types of the sources in the solar neighborhood and compare them with those measured for the GRXE. Our source sample includes 6 symbiotic stars (SSs), 16 intermediate polars (IPs), 3 polars, 16 quiescent dwarf novae (DNe) and 4 active binaries (ABs). We find that the mean equivalent width ($EW_{6.7}$) of the 6.7-keV line and the mean 7.0/6.7-keV line ratio are $107\\pm16.0$ eV and $0.71\\pm 0.04$ for intermediate polars and $221\\pm 135$ eV and $0.44\\pm 0.14$ for polars, respectively, which are all substantially different from those ($490\\pm15 $~eV and $...

  11. Some updates on the role of magnetic fields in Cataclysmic variables

    Directory of Open Access Journals (Sweden)

    Coel Hellier

    2004-01-01

    Full Text Available En este resumen se cubren algunos aspectos de los recientes desarrollos en la comprensi on del papel que juegan los campos magn eticos en variables catacl smicas: presento una discusi on sobre los recientes modelos de uni caci on DNO{QPO; los l mites de la magnetosfera del disco; algunas cuestiones relacionadas con la componente suave de cuerpo negro y la naturaleza de los espectros de rayos X en MCVs; si las estellas SW Sex son magn eticas; y nalmente, menciono el raro comportamiento de FS Aur y HS 2331+3905.

  12. Observational studies of cataclysmic variable evolution: Of samples, biases and surprises

    Directory of Open Access Journals (Sweden)

    B.T. Gansicke

    2004-01-01

    Full Text Available Presento un breve informe sobre el estado de tres grandes proyectos observacionales destinados a veri car nuestra actual comprensi on de la evoluci on de variables catacl smicas (CVs: la selecci on espectrosc opica de las nuevas CVs en el Hamburg Quasar Survey, la b usqueda de pre-CVs bas andose en los colores de Sloan y en la espectroscop a multi-objeto UK Schmidt/6dF y la identi caci on de CVs que proceden de binarias de rayos X supersuaves, utilizando el \\survey" espectrosc opico en el ultravioleta lejano del HST/STIS.

  13. Observational studies of cataclysmic variable evolution: Of samples, biases and surprises

    OpenAIRE

    Gansicke, B. T.

    2004-01-01

    Presento un breve informe sobre el estado de tres grandes proyectos observacionales destinados a veri car nuestra actual comprensi on de la evoluci on de variables catacl smicas (CVs): la selecci on espectrosc opica de las nuevas CVs en el Hamburg Quasar Survey, la b usqueda de pre-CVs bas andose en los colores de Sloan y en la espectroscop a multi-objeto UK Schmidt/6dF y la identi caci on de CVs que proceden de binarias de rayos X supersuaves, utilizando el \\survey" espectrosc ...

  14. Doppler Tomography of Cataclysmic Variables with a 6.5-m class Telescope

    Directory of Open Access Journals (Sweden)

    J. Echevarría

    2007-01-01

    Full Text Available Se est llevando a cabo un proyecto a largo plazo de espectroscop a de alta dispersi n (R 20000 para observar y analizar una muestra de variables catacl smicas con el telescopio de 2.1-m en el Observatorio Astron mico Nacional en San Pedro M rtir y el espectr grafo echelle. La herramienta principal para este an lisis es la tomograf a Doppler. En esta contribuci n presentamos nuestro trabajo y abordamos la pregunta: >C mo podr amos mejorar este proyecto con un telescopio de clase 6.5-m?

  15. 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.

  16. Modeling the diverse fuv spectra of disk-dominated Cataclysmic variables

    Directory of Open Access Journals (Sweden)

    Knox S. Long

    2004-01-01

    Full Text Available Los espectros de FUSE y HST de novas enanas en explosiones y de variables semejantes a novas presentan un amplio rango de caracter sticas. En unos cuantos sistemas existen se~nales obvias de un viento r apido en la forma de los per les de OVI semejantes a P-Cygni y de otros iones en relativamente altos estados de ionizaci on. Pero estos casos son raros. Son m as comunes los sistemas con espectros FUV que presentan una compleja mezcla de l neas de alto y bajo estado de ionizaci on. Se describen intentos para reproducir los espectros utilizando el c odigo de Monte Carlo de transferencia radiativa, desarrollado para modelar vientos bic onicos en sistemas de disco.

  17. The X-ray properties of the magnetic Cataclysmic Variable UU Col

    CERN Document Server

    De Martino, D; Mukai, K; Bonnet-Bidaud, J M; Burwitz, V; Gänsicke, B T; Haberl, F; Mouchet, M

    2006-01-01

    XMM-Newton observations aimed at determining for the first time the broad-band X-ray properties of the faint high galactic latitude Intermediate Polar UU Col are presented. We performed X-ray timing analysis in different energy ranges of the EPIC cameras which reveals the dominance of the 863s white dwarf rotational period. The spin pulse is strongly energy dependent. Weak variabilities at the beat 935s and at the 3.5hr orbital periods are also observed, but the orbital modulation is detected only below 0.5keV. Simultaneous UV and optical photometry shows that the spin pulse is anti-phased with respect to the hard X-rays. Analysis of the EPIC and RGS spectra reveals the complexity of the X-ray emission, being composed of a soft 50eV black--body component and two optically thin emission components at 0.2keV and 11keV strongly absorbed by dense material with an equivalent hydrogen column density of 10**(23)cm**(-2) partially (50%) covering the X-ray source. The complex X-ray and UV/optical temporal behaviour in...

  18. Wavelets with Ridges: A High-Resolution Representation of Cataclysmic Variable Time-Series

    CERN Document Server

    Blackman, Claire

    2010-01-01

    Quasi-periodic oscillations and dwarf nova oscillations occur in dwarf novae and nova-like variables during outburst and occasionally during quiescence, and have analogues in high-mass X-ray binaries and black-hole candidates. The frequent low coherence of quasi-period oscillations and dwarf nova oscillations can make detection with standard time-series tools such as periodograms problematic. This paper develops tools to analyse quasi-periodic brightness oscillations. We review the use of time-frequency representations in the astronomical literature, and show that representations such as the Choi-Williams Distribution and Zhao-Atlas-Marks Representation, which are best suited to high signal-to-noise data, cannot be assumed a priori to be the best techniques for our data, which have a much higher noise level and lower coherence. This leads us to a detailed analysis of the time-frequency resolution and statistical properties of six time-frequency representations. We conclude that the wavelet scalogram, with the...

  19. Three New Variable Stars in Indus

    CERN Document Server

    Golovin, Alex; Virnina, Natalia; Santiago, Javier Lopez

    2009-01-01

    We report the discovery of three new variable stars in Indus: USNO-B1.0 0311-0760061, USNO-B1.0 0309-0771315, and USNO-B1.0 0315-0775167. Light curves of 3712 stars in a 87' x 58' field centered on the asynchronous polar CD Ind were obtained using a remotely controlled 150 mm telescope of Tzec Maun Observatory (Pingelly, Western Australia). The VaST software based on SExtractor package was used for semi-automatic search for variable stars. We suggest the following classification for the newly discovered variable stars: USNO-B1.0 0311-0760061 - RR Lyr-type, USNO-B1.0 0309-0771315 - W UMa-type, and USNO-B1.0 0315-0775167 - W UMa-type.

  20. Photometric Variability of Four Coronally Active Stars

    Indian Academy of Sciences (India)

    J. C. Pandey; K. P. Singh; R. Sagar; S. A. Drake

    2002-03-01

    We present photometric observations of four stars that are optical counterparts of soft X-ray/EUV sources, namely 1ES 0829+15.9, 1ES0920-13.6, 2RE J110159+223509 and 1ES 1737+61.2. We have discovered periodic variability in two of the stars, viz., MCC 527 (1ES 0829+15.9; Period = 0.828 ± 0.0047) and HD 81032 (1ES 0920-13.6; Period = ∼ 57.02 ± 0.560 days). HD 95559 (2RE J110159+223509) is found to show a period of 3. HD 160934 (1ES1737+61.2) also shows photometric variability but needs to be monitored further for finding its period. These stars most likely belong to the class of chromospherically active stars.

  1. Simple nonlinear models suggest variable star universality

    CERN Document Server

    Lindner, John F; Kia, Behnam; Hippke, Michael; Learned, John G; Ditto, William L

    2015-01-01

    Dramatically improved data from observatories like the CoRoT and Kepler spacecraft have recently facilitated nonlinear time series analysis and phenomenological modeling of variable stars, including the search for strange (aka fractal) or chaotic dynamics. We recently argued [Lindner et al., Phys. Rev. Lett. 114 (2015) 054101] that the Kepler data includes "golden" stars, whose luminosities vary quasiperiodically with two frequencies nearly in the golden ratio, and whose secondary frequencies exhibit power-law scaling with exponent near -1.5, suggesting strange nonchaotic dynamics and singular spectra. Here we use a series of phenomenological models to make plausible the connection between golden stars and fractal spectra. We thereby suggest that at least some features of variable star dynamics reflect universal nonlinear phenomena common to even simple systems.

  2. Photometric Variability of the Be Star Population

    CERN Document Server

    Labadie-Bartz, Jonathan; McSwain, M Virginia; Bjorkman, J E; Bjorkman, K S; Lund, Michael B; Rodriguez, Joseph E; Stassun, Keivan G; Stevens, Daniel J; Gaudi, B Scott; James, David J; Kuhn, Rudolf B; Siverd, Robert J; Beatty, Thomas G

    2016-01-01

    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, baseline of up to ten 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 fracti...

  3. 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

  4. Variable stars identification in digitized photographic data

    CERN Document Server

    Sokolovsky, K V; Zubareva, A M; Samus, N N; Antipin, S V

    2016-01-01

    We identify 339 known and 316 new variable stars of various types among 250000 lightcurves obtained by digitizing 167 30x30cm photographic plates of the Moscow collection. We use these data to conduct a comprehensive test of 18 statistical characteristics (variability indices) in search for the best general-purpose variability detection statistic. We find that the highest peak on the DFT periodogram, interquartile range, median absolute deviation, and Stetson's L index are the most efficient in recovering variable objects from the set of photographic lightcurves used in our test.

  5. Mass Loss and Variability in Evolved Stars

    OpenAIRE

    Marengo, Massimo

    2014-01-01

    Mass loss and variability are two linked, fundamental properties of evolved stars. In this paper I review our current understanding of these processes, with a particular focus on how observations and models are used to constrain reliable mass loss prescriptions for stellar evolution and population synthesis models.

  6. SPECTRAL VARIABILITY OF ROMANO'S STAR

    Directory of Open Access Journals (Sweden)

    O. Maryeva

    2010-01-01

    Full Text Available Combinamos observaciones espectroscópicas de archivo de la estrella LBV V532 (conocida como Estrella de Romano con fotometría en la banda B. Los datos espectroscópicos cubren un intervalo de 15 años, desde 1992 hasta 2007. Mostramos que en máximo de brillo el objeto se comporta como una supergigante con líneas de emisión, mientras que en mínimo V532 se mueve a lo largo de la secuencia de las estrellas WN tardías. En este sentido, la estrella tiene un comportamiento similar al de las bien conocidas variables luminosas azules (LBV: luminous blue variables AG Car y R 127, pero es un poco más caliente en mínimo. Identificamos unas 100 líneas espectrales en el intervalo 3700¿7300 °A. Nuestra espectroscopía para este objeto es la más completa en la actualidad. Obtenemos la velocidad del viento usando las líneas del triplete de He I (300 ± 30 km s¿1. También estimamos los parámetros físicos de la nebulosidad que rodea a V532.

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

    Energy Technology Data Exchange (ETDEWEB)

    Schlegel, E. M.; Shipley, H. V. [Department of Physics and Astronomy, University of Texas-San Antonio, San Antonio, TX 78249 (United States); Rana, V. R. [Space Radiation Laboratory, Caltech, Pasadena, CA 91125 (United States); Barrett, P. E. [US Naval Observatory, Washington, DC 20392-5420 (United States); Singh, K. P., E-mail: eric.schlegel@utsa.edu, E-mail: vrana@srl.caltech.edu, E-mail: barrett.paul@usno.navy.mil, E-mail: singh@tifr.res.in [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai (India)

    2014-12-10

    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{sup 12} to >10{sup 16} cm{sup –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.

  8. Deep MMT Transity Survey of the Open Cluster M37 II: Variable Stars

    CERN Document Server

    Hartman, J D; Holman, M J; McLeod, B A; Stanek, K Z; Barranco, J A; Pinsonneault, M H; Singh-Kalirai, J

    2007-01-01

    We have conducted a deep (15 ~ 500) of these variables are most likely rapidly rotating young low mass stars that are members of the cluster. We identify and analyze five particularly interesting individual variables including a previously identified variable which we suggest is probably a hybrid gamma-Doradus/delta-Scuti pulsator, an enigmatic white dwarf or subdwarf B star that shows pulsation like variations with a period of 0.157728 +- 0.00001 days and an amplitude of 0.07 mag in r, a possible quiescent cataclysmic variable, a detached eclipsing binary (DEB) with at least one gamma-Doradus pulsating component (only the second such variable found in an eclipsing binary), and a low mass (M_{P} ~ M_{S} ~ 0.6 M_{\\odot}) DEB that is a possible cluster member. A preliminary determination of the physical parameters for the DEB+gamma-Doradus system yields M_{P} = 1.58 +- 0.04 M_{\\odot}, M_{S} = 1.58 +- 0.04 M_{\\odot}, R_{P} = 1.39 +- 0.07 R_{\\odot} and R_{S} = 1.38 +- 0.07 R_{\\odot}.

  9. Exploring the crowded central region of 10 Galactic globular clusters using EMCCDs. Variable star searches and new discoveries

    CERN Document Server

    Jaimes, R Figuera; Skottfelt, J; Kains, N; Jørgensen, U G; Horne, K; Dominik, M; Alsubai, K A; Bozza, V; Novati, S Calchi; Ciceri, S; D'Ago, G; Galianni, P; Gu, S -H; Harpsøe, K B W; Haugbølle, T; Hinse, T C; Hundertmark, M; Juncher, D; Korhonen, H; Liebig, C; Mancini, L; Popovas, A; Rabus, M; Rahvar, S; Scarpetta, G; Schmidt, R W; Snodgrass, C; Southworth, J; Starkey, D; Street, R A; Surdej, J; Wang, X -B; Wertz, O

    2015-01-01

    Obtain time-series photometry of the very crowded central regions of Galactic globular clusters with better angular resolution than previously achieved with conventional CCDs on ground-based telescopes to complete, or improve, the census of the variable star population in those stellar systems. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD and the short-exposure-time images obtained (10 images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. The light curves of 12541 stars in the cores of 10 globular clusters were statistically analysed in order to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 L, 2 SR, 20 RR Lyrae, 1 SX Phe, 3 cataclysmic variables, 1 EW a...

  10. Of Variability, or its Absence, in HgMn Stars

    CERN Document Server

    Turcotte, S

    2003-01-01

    Current models and observations of variability in HgMn stars disagree. We present here the models that argue for pulsating HgMn stars with properties similar to those of Slowly Pulsating B Stars. The lack of observed variable HgMn stars suggests that some physical process is missing from the models. Some possibilities are discussed.

  11. OMC automatic variable star classifi cation

    Science.gov (United States)

    López del Fresno, M.; Sarro Baro, L. M.; Solano Márquez, E.

    2013-05-01

    The Optical Monitoring Camera (OMC), on-board the ESA mission INTEGRAL, has stored more than 190.000 light curves for almost 10 years. Among the targets included in its input catalogue there is a relevant amount of variable stars. In many cases, OMC has gathered photometric information of sufficient quality to enable a stellar variability analysis of those stars. In this contribution we show the full pipeline of our classification system, from the period calculation to the final membership classification. We also include relevant points of the system such as the parameters used for filtering good quality light curves, specific optimizations applied to the classification algorithms and an overview of the results obtained.

  12. Variability of the Spin Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya

    CERN Document Server

    Andronov, Ivan L

    2013-01-01

    The observations of the two-periodic magnetic cataclysmic system EX Hya have been carried out, using the telescopes RC16 and TOA-150 of the Tzec Maun observatory. 6 nights of observations were obtained in 2010-2011 (alternatively changing filters VR). Also the databases of WASP, ASAS and AAVSO have been analyzed. Processing time series was carried out using the program MCV. We analyzed changes in the rotation period of the white dwarf, and based on our own and previously published moments of maximum. The ephemeris was determined for the maxima of the radiation flux associated with the rotation of the magnetic white dwarf: Tmax=2437699.89079(59) +0.0465464808(69).E-6.3(2)*10^{-13}E^2, which corresponds to the characteristic timescale of the rotation spin-up of 4.67(14)*10^6 years. This contradicts the estimated value of the mass of the white dwarf of 0.42M_\\odot, based on X-ray observations made by Yuasa et al (2010), however, is consistent with estimates of the masses of 0.79 M_\\odot (white dwarf) and 0.108 M...

  13. Temporal Variability of Stars and Stellar Systems

    CERN Document Server

    Lister, T A; Brown, T M; Street, R A

    2009-01-01

    Although the Sun is our closest star by many orders of magnitude and despite having sunspot records stretching back to ancient China, our knowledge of the Sun's magnetic field is far from complete. Indeed, even now, after decades of study, the most obvious manifestations of magnetic fields in the Sun (e.g. sunspots, flares and the corona) are scarcely understood at all. These failures in spite of intense effort suggest that to improve our grasp of magnetic fields in stars and of astrophysical dynamos in general, we must broaden our base of examples beyond the Sun; we must study stars with a variety of ages, masses, rotation rates, and other properties, so we can test models against as broad a range of circumstances as possible. Over the next decade, an array of indirect techniques will be supplemented by rapidly maturing new capabilities such as gyrochronology, asteroseismology and precision photometry from space, which will transform our understanding of the temporal variability of stars and stellar systems....

  14. 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.

  15. Periodic signals from the Circinus region: two new cataclysmic variables and the ultraluminous X-ray source candidate GC X-1

    CERN Document Server

    Esposito, P; Milisavljevic, D; Mapelli, M; Zampieri, L; Sidoli, L; Fabbiano, G; Castillo, G A Rodríguez

    2015-01-01

    The examination of two 2010 Chandra ACIS exposures of the Circinus galaxy resulted in the discovery of two pulsators: CXO J141430.1-651621 and CXOU J141332.9-651756. We also detected 26-ks pulsations in CG X-1, consistently with previous measures. For ~40 other sources, we obtained limits on periodic modulations. In CXO J141430.1-651621, which is ~2 arcmin outside the Circinus galaxy, we detected signals at 6120(1) s and 64.2(5) ks. In the longest observation, the source showed a flux of ~1.1e-13 erg/cm^2/s (absorbed, 0.5-10 keV) and the spectrum could be described by a power-law with photon index ~1.4. From archival observations, we found that the luminosity is variable by ~50 per cent on time-scales of weeks-years. The two periodicities pin down CXO J141430.1-651621 as a cataclysmic variable of the intermediate polar subtype. The period of CXOU J141332.9-651756 is 6378(3) s. It is located inside the Circinus galaxy, but the low absorption indicates a Galactic foreground object. The flux was ~5e-14 erg/cm^2/...

  16. Variability survey of brightest stars in selected OB associations

    CERN Document Server

    Laur, Jaan; Eenmäe, Tõnis; Tuvikene, Taavi; Leedjärv, Laurits

    2016-01-01

    The stellar evolution theory of massive stars remains uncalibrated with high-precision photometric observational data mainly due to a small number of luminous stars that are monitored from space. Automated all-sky surveys have revealed numerous variable stars but most of the luminous stars are often overexposed. Targeted campaigns can improve the time base of photometric data for those objects. The aim of this investigation is to study the variability of luminous stars at different timescales in young open clusters and OB associations. We monitored 22 open clusters and associations from 2011 to 2013 using a 0.25-m telescope. Variable stars were detected by comparing the overall light-curve scatter with measurement uncertainties. Variability was analysed by the light curve feature extraction tool FATS. Periods of pulsating stars were determined using the discrete Fourier transform code SigSpec. We then classified the variable stars based on their pulsation periods and available spectral information. We obtaine...

  17. Searching for Variable Stars in and around Open Clusters

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    We present a snapshot of our recent results of a variable star survey in1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A totalnumber of 39 variable stars are newly discovered, including 22 W UMa stars, 10EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassifiedvariables.

  18. THE CATALINA SURVEYS PERIODIC VARIABLE STAR CATALOG

    Energy Technology Data Exchange (ETDEWEB)

    Drake, A. J.; Graham, M. J.; Djorgovski, S. G.; Mahabal, A. A.; Donalek, C.; Williams, R. [California Institute of Technology, 1200 East California Boulevard, CA 91225 (United States); Catelan, M.; Torrealba, G. [Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Facultad de Física, Av. Vicuña Mackena 4860, 782-0436 Macul, Santiago (Chile); García-Álvarez, D. [Instituto de Astrofísica de Canarias, Avenida Vía Láctea, E-38205 La Laguna, Tenerife (Spain); Prieto, J. L.; Beshore, E. [Department of Astronomy, Princeton University, 4 Ivy Ln., Princeton, NJ 08544 (United States); Larson, S.; Christen sen, E.; Boattini, A.; Gibbs, A.; Hill, R.; Kowalski, R.; Johnson, J. [Department of Planetary Sciences, Lunar and Planetary Laboratory, The University of Arizona, 1629 East University Boulevard, Tucson, AZ 85721 (United States); Belokurov, V.; Koposov, S. E. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); and others

    2014-07-01

    We present ∼47,000 periodic variables found during the analysis of 5.4 million variable star candidates within a 20,000 deg{sup 2} region covered by the Catalina Surveys Data Release-1 (CSDR1). Combining these variables with type ab RR Lyrae from our previous work, we produce an online catalog containing periods, amplitudes, and classifications for ∼61,000 periodic variables. By cross-matching these variables with those from prior surveys, we find that >90% of the ∼8000 known periodic variables in the survey region are recovered. For these sources, we find excellent agreement between our catalog and prior values of luminosity, period, and amplitude as well as classification. We investigate the rate of confusion between objects classified as contact binaries and type c RR Lyrae (RRc's) based on periods, colors, amplitudes, metallicities, radial velocities, and surface gravities. We find that no more than a few percent of the variables in these classes are misidentified. By deriving distances for this clean sample of ∼5500 RRc's, we trace the path of the Sagittarius tidal streams within the Galactic halo. Selecting 146 outer-halo RRc's with SDSS radial velocities, we confirm the presence of a coherent halo structure that is inconsistent with current N-body simulations of the Sagittarius tidal stream. We also find numerous long-period variables that are very likely associated within the Sagittarius tidal stream system. Based on the examination of 31,000 contact binary light curves we find evidence for two subgroups exhibiting irregular light curves. One subgroup presents significant variations in mean brightness that are likely due to chromospheric activity. The other subgroup shows stable modulations over more than a thousand days and thereby provides evidence that the O'Connell effect is not due to stellar spots.

  19. Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6397: Evidence for a Bimodal Cataclysmic Variable Population

    CERN Document Server

    Cohn, Haldan N; Couch, Sean M; Anderson, Jay; Cool, Adrienne M; Berg, Maureen van den; Bogdanov, Slavko; Heinke, Craig O; Grindlay, Jonathan E; 10.1088/0004-637X/722/1/20

    2011-01-01

    We have searched for optical identifications for 79 Chandra X-ray sources that lie within the half-mass radius of the nearby, core-collapsed globular cluster NGC 6397, using deep Hubble Space Telescope Advanced Camera for Surveys Wide Field Channel imaging in H-alpha, R, and B. Photometry of these images allows us to classify candidate counterparts based on color-magnitude diagram location. In addition to recovering nine previously detected cataclysmic variables (CVs), we have identified six additional faint CV candidates, a total of 42 active binaries (ABs), two millisecond pulsars (MSPs), one candidate active galactic nucleus, and one candidate interacting galaxy pair. Of the 79 sources, 69 have a plausible optical counterpart. The 15 likely and possible CVs in NGC 6397 mostly fall into two groups: a brighter group of six for which the optical emission is dominated by contributions from the secondary and accretion disk, and a fainter group of seven for which the white dwarf dominates the optical emission. T...

  20. MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters - II. Cataclysmic variables - progenitors and population at birth

    Science.gov (United States)

    Belloni, Diogo; Giersz, Mirek; Rocha-Pinto, Helio J.; Leigh, Nathan W. C.; Askar, Abbas

    2016-10-01

    This is the second in a series of papers associated with cataclysmic variables (CVs) and related objects, formed in a suite of simulations for globular cluster evolution performed with the MOCCA Monte Carlo code. We study the properties of our simulated CV populations throughout the entire cluster evolution. We find that dynamics extends the range of binary CV progenitor properties, causing CV formation from binary progenitors that would otherwise not become CVs. The CV formation rate in our simulations can be separated into two regimes: an initial burst (≲ 1 Gyr) connected with the formation of the most massive WDs, followed by a nearly constant formation rate. This result holds for all models regardless of the adopted initial conditions, even when most CVs form dynamically. Given the cluster age-dependence of CV properties, we argue that direct comparisons to observed Galactic field CVs could be misleading, since cluster CVs can be up to 4 times older than their field counterparts. Our results also illustrate that, due mainly to unstable mass transfer, some CVs that form in our simulations are destroyed before the present-day. Finally, some field CVs might have originated from GCs, as found in our simulations, although the fraction of such escapers should be small relative to the entire Galactic field CV population.

  1. MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters - II. Cataclysmic variables - progenitors and population at birth

    Science.gov (United States)

    Belloni, Diogo; Giersz, Mirek; Rocha-Pinto, Helio J.; Leigh, Nathan W. C.; Askar, Abbas

    2017-02-01

    This is the second in a series of papers associated with cataclysmic variables (CVs) and related objects, formed in a suite of simulations for globular cluster evolution performed with the MOCCA Monte Carlo code. We study the properties of our simulated CV populations throughout the entire cluster evolution. We find that dynamics extends the range of binary CV progenitor properties, causing CV formation from binary progenitors that would otherwise not become CVs. The CV formation rate in our simulations can be separated into two regimes: an initial burst (≲1 Gyr) connected with the formation of the most massive white dwarfs, followed by a nearly constant formation rate. This result holds for all models regardless of the adopted initial conditions, even when most CVs form dynamically. Given the cluster age-dependence of CV properties, we argue that direct comparisons to observed Galactic field CVs could be misleading, since cluster CVs can be up to four times older than their field counterparts. Our results also illustrate that, due mainly to unstable mass transfer, some CVs that form in our simulations are destroyed before the present day. Finally, some field CVs might have originated from globular clusters, as found in our simulations, although the fraction of such escapers should be small relative to the entire Galactic field CV population.

  2. MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters -- II. Cataclysmic variables -- progenitors and population at birth

    CERN Document Server

    Belloni, Diogo; Rocha-Pinto, Helio J; Leigh, Nathan; Askar, Abbas

    2016-01-01

    This is the second in a series of papers associated with cataclysmic variables (CVs) and related objects, formed in a suite of simulations for globular cluster evolution performed with the MOCCA Monte Carlo code. We study the properties of our simulated CV populations throughout the entire cluster evolution. We find that dynamics extends the range of binary CV progenitor properties, causing CV formation from binary progenitors that would otherwise not become CVs. The CV formation rate in our simulations can be separated into two regimes: an initial burst ($\\lesssim$ 1 Gyr) connected with the formation of the most massive WDs, followed by a nearly constant formation rate. This result holds for all models regardless of the adopted initial conditions, even when most CVs form dynamically. Given the cluster age-dependence of CV properties, we argue that direct comparisons to observed Galactic field CVs could be misleading, since cluster CVs can be up to 4 times older than their field counterparts. Our results also...

  3. Discovery of Three Variable Stars in Direction toward NGC 4565

    Institute of Scientific and Technical Information of China (English)

    Lei Li; Hong Wu; Xiao-Bin Zhang; Ya-Bo Wu; Xu Zhou; Zhao-Ji Jiang; Jun Ma

    2004-01-01

    We present the results of a variable star search in a field next to the edgeon galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discovered. Based on spectra obtained from the 2.16 m NAOC telescope, we identify two of these as RR Lyr stars and one as a special T Tauri star.

  4. Variable Stars in the Globular Cluster NGC 4590 (M68

    CERN Document Server

    Sariya, Devesh Path; Yadav, R K S

    2013-01-01

    We present results of time series photometry to search for variable stars in the field of metal-poor globular cluster NGC 4590 (M68). Periods have been revised for 40 known variables and no significant changes were found. A considerable change in Blazhko effect for V25 has been detected. Among nine newly discovered variable candidates, 5 stars are of RRc Bailey type variables while 4 stars are unclassified. The variable stars V10, V21, V50 and V51 are found to be cluster members based on the radial velocity data taken from literature.

  5. Variable stars in the globular cluster NGC 4590 (M68)

    Science.gov (United States)

    Sariya, Devesh P.; Lata, Sneh; Yadav, R. K. S.

    2014-02-01

    We present results of time series photometry to search for variable stars in the field of metal-poor globular cluster NGC 4590 (M68). Periods have been revised for 40 known variables and no significant changes were found. A considerable change in Blazhko effect for V25 has been detected. Among nine newly discovered variable candidates, 5 stars are of RRc Bailey type variables while 4 stars are unclassified. The variable stars V10, V21, V50 and V51 are found to be cluster members based on the radial velocity data taken from literature.

  6. 激变变星及相关天体的与近红外电离钙三重线的光谱分析%Spectroscopy around and Ca II Triplet of Cataclysmic Variables and Related Objects

    Institute of Scientific and Technical Information of China (English)

    刘学富; 陈阳; 黄河

    2000-01-01

    给出了1997年4月15日至17日在北京天文台用2.16 m望远镜卡焦光谱仪观测获得的6颗激变变星 (AB Boo, UX UMa, T CrB, AH Her, Z Cam 和 V426 Oph) 及3颗相关天体(UMa3, EG UMa 和 Leo3)的CCD光谱, 并同时拍摄了5颗晚型星(3 Dra, Vir, Leo, 34 Boo 和36Com) 的CCD 光谱, 作为晚型星参考谱. 测量了观测样本星的和近红外Ca II的三重线(8498, 8542和 8662)的等值宽度(EW),谱线半极大全宽(FWHM)和视向速度(Vr), 并分析了这些星的活动性.%In this paper, some CCD spectra of 6 cataclysmic variables: AB Boo, T CrB, UX UMa, AH Her, Z Cam, V426 Oph and 3 related objects: Leo3, UMa3 and EG UMa are presented. We also observed 5 late-type stars: 3 Dra, Vir, Leo, 34 Boo, and 36 Com in order to provide comparison with the late-type component of the program systems. The observations were made using the 2.16 m telescope of Bejing Observatory with a Cassergrain spectrograph on 1997—04—15/17 at the Xinglong Station. The CCD spectra were obtained with a low resolution and a dispersion of 1.2/pixel. The spectral region covered is from 5920 to 7072, and from 7950 to 9180 for all the program stars and only 3390—8380 for AH Her. Representative spectra are given for each object. The equivalent width (EW) and FWHM of and CaII triplet lines were determined. The radial velocities for 9 program stars were also determined. Implications of our results are discussed.

  7. Dynamical mass transfer in cataclysmic binaries

    Science.gov (United States)

    Melia, Fulvio; Lamb, D. Q.

    1987-01-01

    When a binary comes into contact and mass transfer begins, orbital angular momentum is stored in the accretion disk until the disk couples tidally to the binary system. Taam and McDermott (1987) have suggested that this leads to unstable dynamical mass transfer in many cataclysmic variables in which mass transfer would otherwise be stable, and that it explains the gap between 2 and 3 h in the orbital period distribution of these systems. Here the consequences of this hypothesis for the evolution of cataclysmic binaries are explored. It is found that systems coming into contact longward of the period gap undergo one or more episodes of dynamical mass transfer.

  8. Optical Studies of Twenty Longer-Period Cataclysmic Binaries

    CERN Document Server

    Thorstensen, John R; Skinner, Julie N

    2010-01-01

    We obtained time-series radial velocity spectroscopy of twenty cataclysmic variable stars, with the aim of determining orbital periods P_orb. All of the stars reported here prove to have P_orb > 3.5 h. For sixteen of the stars, these are the first available period determinations, and for the remaining four (V709 Cas, AF Cam, V1062 Tau, and RX J2133+51) we use new observations to improve the accuracy of previously-published periods. Most of the targets are dwarf novae, without notable idiosyncracies. Of the remainder, three (V709 Cas, V1062 Tau, and RX J2133+51) are intermediate polars (DQ Her stars); one (IPHAS 0345) is a secondary-dominated system without known outbursts, similar to LY UMa; one (V1059 Sgr) is an old nova; and two others (V478 Her and V1082 Sgr) are long-period novalike variables. The stars with new periods are IPHAS 0345 (0.314 d); V344 Ori (0.234 d); VZ Sex (0.149 d); NSVS 1057+09 (0.376 d); V478 Her (0.629 d); V1059 Sgr (0.286 d); V1082 Sgr (0.868 d); FO Aql (0.217 d); V587 Lyr (0.275 d); ...

  9. Searching for Variable Stars in the Field of NGC 7789

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    We present the results of a time-series CCD photometric survey ofvariable stars in the field of the open cluster NGC 7789. In a field of about onedegree centering on the cluster, a total of 28 new variable stars are discovered(14 W UMa systems, nine EA-type eclipsing binaries, one RR Lyr star, and fourunclassified). In addition, we recovered 11 old variables previously discovered byother authors. Preliminary parameters are given for some of these variables.

  10. Variability survey of brightest stars in selected OB associations

    Science.gov (United States)

    Laur, Jaan; Kolka, Indrek; Eenmäe, Tõnis; Tuvikene, Taavi; Leedjärv, Laurits

    2017-02-01

    Context. The stellar evolution theory of massive stars remains uncalibrated with high-precision photometric observational data mainly due to a small number of luminous stars that are monitored from space. Automated all-sky surveys have revealed numerous variable stars but most of the luminous stars are often overexposed. Targeted campaigns can improve the time base of photometric data for those objects. Aims: The aim of this investigation is to study the variability of luminous stars at different timescales in young open clusters and OB associations. Methods: We monitored 22 open clusters and associations from 2011 to 2013 using a 0.25-m telescope. Variable stars were detected by comparing the overall light-curve scatter with measurement uncertainties. Variability was analysed by the light curve feature extraction tool FATS. Periods of pulsating stars were determined using the discrete Fourier transform code SigSpec. We then classified the variable stars based on their pulsation periods and available spectral information. Results: We obtained light curves for more than 20 000 sources of which 354 were found to be variable. Amongst them we find 80 eclipsing binaries, 31 α Cyg, 13 β Cep, 62 Be, 16 slowly pulsating B, 7 Cepheid, 1 γ Doradus, 3 Wolf-Rayet and 63 late-type variable stars. Up to 55% of these stars are potential new discoveries as they are not present in the Variable Star Index (VSX) database. We find the cluster membership fraction for variable stars to be 13% with an upper limit of 35%. Variable star catalogue (Tables A.1-A.10) and light curves are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A108

  11. Felix de Roy: a life of variable stars

    CERN Document Server

    Shears, Jeremy

    2010-01-01

    Felix de Roy (1883-1942), an internationality recognised amateur astronomer, made significant contributions to variable star research. As an active observer, he made some 91,000 visual estimates of a number of different variable stars. A Belgian national, he took refuge in England during World War 1. While there, de Roy became well enough known to later serve as Director of the BAA Variable Star Section for seventeen years. Through this office, and his connections with other organisations around the world, he encouraged others to pursue the observation of variable stars. Not merely content to accumulate observational data, de Roy also analysed the data and published numerous papers.

  12. Clustering Based Feature Learning on Variable Stars

    CERN Document Server

    Mackenzie, Cristóbal; Protopapas, Pavlos

    2016-01-01

    The success of automatic classification of variable stars strongly depends on the lightcurve representation. Usually, lightcurves are represented as a vector of many statistical descriptors designed by astronomers called features. These descriptors commonly demand significant computational power to calculate, require substantial research effort to develop and do not guarantee good performance on the final classification task. Today, lightcurve representation is not entirely automatic; algorithms that extract lightcurve features are designed by humans and must be manually tuned up for every survey. The vast amounts of data that will be generated in future surveys like LSST mean astronomers must develop analysis pipelines that are both scalable and automated. Recently, substantial efforts have been made in the machine learning community to develop methods that prescind from expert-designed and manually tuned features for features that are automatically learned from data. In this work we present what is, to our ...

  13. Sky catalogue 2000.0. Volume 2: Double stars, variable stars and nonstellar objects.

    Science.gov (United States)

    Hirshfeld, A.; Sinnott, R. W.

    This is a re-issue of a book first published in 1985 (see Abstr. 39.002.019). This is a standard reference work for telescope users which gives positional and other data for galaxies, double and variable stars, and star clusters. It includes tables on 20,000 objects. Comprehensive treatment is given for each object: position for epoch 2000.0, magnitudes in the UBV photometric system, color index, surface brightness and Hubble classification for galaxies. Contents: Glossary of selected astronomical names. Index to letter names of variable stars. Double and multiple stars. Visual binary stars. Spectroscopic binary stars. Variable stars. Suspected variable stars. Open clusters. Open cluster cross index. Globular clusters. Bright nebulae. Dark nebulae. Planetary nebulae. Galaxies. Quasi-stellar objects (QSO's). Radio sources. X-ray sources.

  14. New Low Accretion-Rate Magnetic Binary Systems and their Significance for the Evolution of Cataclysmic Variables

    CERN Document Server

    Schmidt, G D; Vanlandingham, K M; Anderson, S F; Barentine, J C; Brewington, H J; Hall, P B; Harvanek, M; Kleinman, S J; Krzesínski, J; Long, D; Margon, B; Neilsen, E H; Newman, P R; Nitta, A; Schneider, D P; Snedden, S A

    2005-01-01

    Discoveries of two new white dwarf plus M star binaries with striking optical cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to six the total number of X-ray faint, magnetic accretion binaries that accrete at rates 3 hr. Optical surveys for the cyclotron harmonics appear to be the only means of discovery, so the space density of pre-Polars could rival that of Polars, and the binaries provide an important channel of progenitors (in addition to the asynchronous Intermediate Polars). Both physical and SDSS observational selection effects are identified that may help to explain the clumping of all six systems in a narrow range of magnetic field strength around 60 MG.

  15. 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.

  16. Period Changes and Evolution in Pulsating Variable Stars

    CERN Document Server

    Neilson, Hilding R; Smith, Horace A

    2016-01-01

    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.

  17. Data Mining of Cataclysmic Variables Candidates in Massive Spectra%海量光谱中激变变星候选体的数据挖掘

    Institute of Scientific and Technical Information of China (English)

    姜斌; 罗阿理; 赵永恒

    2011-01-01

    提出一套适用于海量光谱自动快速筛选激变变星的方法.利用已证认的激变变星光谱作为模板,使用主分量分析提取主特征后构造光谱特征矩阵,将海量光谱利用光谱特征矩阵映射到特征空间后,使用支持向量机排除大部分非候选体,最后对较少数量的候选体进行模板匹配并证认,结果作为反馈进一步丰富模板库.实验发现了58个新的激变变星候选体,表明了该方法的可行性,为在LAMOST海量光谱中快速搜索激变变星等稀少天体提供了有效途径.%An automatic and efficient method for LAMOST's massive spectral data reduction is presented in this paper. The identified cataclysmic variables were selected as templates to construct the feature space by PCA(the principal component analysis), and most of the non-candidates were excluded by the method using support vector machine. Template matching strategy was used to identify the final candidates which were analyzed to complement the templates as feedback. Fifty eight new CVs candidates were found in the experiment, showing that our approach to finding special celestial bodies can be practical in LAM-OST.

  18. A close hidden stellar companion to the SX Phe-type variable star DW Psc

    Energy Technology Data Exchange (ETDEWEB)

    Qian, S.-B.; Li, L.-J.; Wang, S.-M.; He, J.-J.; Zhou, X.; Jiang, L.-Q., E-mail: qsb@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences (CAS), P.O. Box 110, 650011 Kunming (China)

    2015-01-01

    DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the observed-calculated (O-C) diagram are analyzed. It is discovered that the O-C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion (M{sub 2}sini∼0.45(±0.03) M{sub ⊙}). The two-component stars in the binary system are orbiting each other in an eccentric orbit (e ∼ 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Roche-lobe overflow, and the system may be a progenitor of a cataclysmic variable. The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future.

  19. Unusual Variabilities in the Atmosphere of the Star 55 CYG

    Science.gov (United States)

    Maharramov, Y. M.

    2010-09-01

    Some unusual spectral features of the star 55 Cyg are presented in the article. Observational data on the variability of hydrogen lines profiles, in particula, the unique observational fact of the disappearance of the Hα profile are presented. Profiles of the line and comparative analysis of the variables observed in the profiles of hydrogen lines of the star are adduced.

  20. The OmegaWhite survey for Short-Period Variable Stars III: Follow-up Photometric and Spectroscopic Observations

    CERN Document Server

    Macfarlane, S 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

    2016-01-01

    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-m 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 also 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 many of these variables have spectra which are consistent with being delta 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 identifie...

  1. The accretion disk in the post period-minimum cataclysmic variable SDSS J080434.20+510349.2

    CERN Document Server

    Zharikov, S; Aviles, A; Michel, R; Gonzalez-Buitrago, D; Garcia-Diaz, Ma T

    2012-01-01

    This study of SDSS0804 is primarily concerned with the double-hump shape in the light curve and its connection with the accretion disk in this bounce-back system. Time-resolved photometric and spectroscopic observations were obtained to analyze the behavior of the system between superoutbursts. A geometric model of a binary system containing a disk with two outer annuli spiral density waves was applied to explain the light curve and the Doppler tomography. Observations were carried out during 2008-2009, after the object's magnitude decreased to V~17.7(0.1) from the March 2006 eruption. The light curve clearly shows a sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min periodicity, which is half of the orbital period of the system. In Sept. 2010, the system underwent yet another superoutburst and returned to its quiescent level by the beginning of 2012. This light curve once again showed a double-humps, but with a significantly smaller ~0.01mag amplitude. Other types of variability like a "mini...

  2. Meta-classification for Variable Stars

    Science.gov (United States)

    Pichara, Karim; Protopapas, Pavlos; León, Daniel

    2016-03-01

    The need for the development of automatic tools to explore astronomical databases has been recognized since the inception of CCDs and modern computers. Astronomers already have developed solutions to tackle several science problems, such as automatic classification of stellar objects, outlier detection, and globular clusters identification, among others. New scientific problems emerge, and it is critical to be able to reuse the models learned before, without rebuilding everything from the beginning when the sciencientific problem changes. In this paper, we propose a new meta-model that automatically integrates existing classification models of variable stars. The proposed meta-model incorporates existing models that are trained in a different context, answering different questions and using different representations of data. A conventional mixture of expert algorithms in machine learning literature cannot be used since each expert (model) uses different inputs. We also consider the computational complexity of the model by using the most expensive models only when it is necessary. We test our model with EROS-2 and MACHO data sets, and we show that we solve most of the classification challenges only by training a meta-model to learn how to integrate the previous experts.

  3. Ernest Elliott Markwick: variable stars and military campaigns

    CERN Document Server

    Shears, Jeremy

    2011-01-01

    Colonel E.E. Markwick, CB, CBE, FRAS (1853 - 1925) pursued a distinguished career in the British Army, serving in Great Britain and other parts of the Empire and rising to the rank of Colonel. He was an original member of the BAA and went on to become President between 1912 and 1914. His main observational interest was the study of variable stars and he independently discovered two variables, RY Sgr and T Cen. He directed the BAA Variable Star Section from 1899 to 1909, organising its work along lines that are largely pursued even to this day and which other variable star organisations around the world have emulated.

  4. 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

  5. Modelling of variability of the chemically peculiar star phi Draconis

    CERN Document Server

    Prvák, Milan; Krtička, Jiří; Mikulášek, Zdeněk; Lüftinger, T

    2015-01-01

    Context: The presence of heavier chemical elements in stellar atmospheres influences the spectral energy distribution (SED) of stars. An uneven surface distribution of these elements, together with flux redistribution and stellar rotation, are commonly believed to be the primary causes of the variability of chemically peculiar (CP) stars. Aims: We aim to model the photometric variability of the CP star PHI Dra based on the assumption of inhomogeneous surface distribution of heavier elements and compare it to the observed variability of the star. We also intend to identify the processes that contribute most significantly to its photometric variability. Methods: We use a grid of TLUSTY model atmospheres and the SYNSPEC code to model the radiative flux emerging from the individual surface elements of PHI Dra with different chemical compositions. We integrate the emerging flux over the visible surface of the star at different phases throughout the entire rotational period to synthesise theoretical light curves of...

  6. MN Dra - a SU UMa-type star during its September 2013 superoutburst

    CERN Document Server

    Bakowska, Karolina; Pospieszynski, Remigiusz

    2016-01-01

    We report CCD photometry of the cataclysmic variable star MN Draconis. During the season of August-September 2013, one normal outburst and one superoutburst were detected. In the light curves of MN Dra clear superhumps were present during September 2013 superoutburst. That fact confirms that the star is a member of SU UMa class.

  7. 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.

  8. The Onset of Chaos in Pulsating Variable Stars

    CERN Document Server

    Turner, David G; Percy, J R; Abdel-Latif, Mohamed Abdel-Sabour

    2011-01-01

    Random changes in pulsation period occur in cool pulsating Mira variables, Type A, B, and C semiregular variables, RV Tauri variables, and in most classical Cepheids. The physical processes responsible for such fluctuations are uncertain, but presumably originate in temporal modifications of the envelope convection in such stars. Such fluctuations are seemingly random over a few pulsation cycles of the stars, but are dominated by the regularity of the primary pulsation over the long term. The magnitude of stochasticity in pulsating stars appears to be linked directly to their dimensions, although not in simple fashion. It is relatively larger in M supergiants, for example, than in short-period Cepheids, but is common enough that it can be detected in visual observations for many types of pulsating stars. Although chaos was discovered in such stars 80 years ago, detection of its general presence in the group has only been possible in recent studies.

  9. Photometric CCD observations of four Pre-cataclysmic binary candidates

    Science.gov (United States)

    Hinojosa, R.; Vogt, N.; Colque, Juan Pablo

    We present preliminary results of differential photometric observations of Abell 65, HZ 9, GD 1401 and BPM 46460, obtained between September and December 2006 with the 42 cm telescope of the Cerro Armazones Observatory which belongs to the Universidad Catolica del Norte, Antofagasta. All four stars are close red dwarf/white dwarf binaries which could have formed be recent common envelope events. In two of the four cases we detected (or confirmed) significant variability. In one of them, the central star of a planetary nebula Abell 65, we confirmed the rather strong photometric variability with a period very near to 24 hours (Bond and Livio, 1990). In the white dwarf binary HZ9 we detected, for the first time, photometric variations with a period near 0.58 days which corresponds to the known orbital period (Lanning and Pesch, 1981; Stauffer, 1987). The amplitude of this variation is 0.08 mag, it probably refers to reflection of the white dwarf radiation on the surface of the red companion. - These observations are part of a larger on-going project which pretends to identify and to study pre-cataclysmic binaries by means of photometric and spectroscopic methods and to improve, this way, the hitherto poor statistics on the properties of these interesting stars.

  10. Nonradial modes in RR Lyrae stars from the OGLE Collection of Variable Stars

    CERN Document Server

    Netzel, Henryka; Moskalik, Pawel

    2016-01-01

    The Optical Gravitational Lensing Experiment (OGLE) is a great source of top-quality photometry of classical pulsators. Collection of variable stars from the fourth part of the project contains more than 38 000 RR Lyrae stars. These stars pulsate mostly in the radial fundamental mode (RRab), in radial first overtone (RRc) or in both modes simultaneously (RRd). Analysis of the OGLE data allowed to detect additional non-radial modes in RRc and in RRd stars. We have found more than 260 double-mode stars with characteristic period ratio of the additional (shorter) period to first overtone period around 0.61, increasing the number of known stars of this type by factor of 10. Stars from the OGLE sample form three nearly parallel sequences in the Petersen diagram. Some stars show more than one non-radial mode simultaneously. These modes belong to different sequences.

  11. Spectroscopic variability of two Oe stars

    CERN Document Server

    Rauw, G; Naze, Y; Eversberg, T; Alves, F; Arnold, W; Bergmann, T; Viegas, N G Correia; Fahed, R; Fernando, A; Gonzalez-Perez, J N; Carreira, L F Gouveia; Hempelmann, A; Hunger, T; Knapen, J H; Leadbeater, R; Dias, F Marques; Mittag, M; Moffat, A F J; Reinecke, N; Ribeiro, J; Romeo, N; Gallego, J Sanchez; Santos, E M Dos; Schanne, L; Schmitt, J H M M; Schroeder, K -P; Stahl, O; Stober, Ba; Stober, Be; Vollmann, K

    2015-01-01

    The Oe stars HD45314 and HD60848 have recently been found to exhibit very different X-ray properties: whilst HD60848 has an X-ray spectrum and emission level typical of most OB stars, HD45314 features a much harder and brighter X-ray emission, making it a so-called gamma Cas analogue. Monitoring the optical spectra could provide hints towards the origin of these very different behaviours. We analyse a large set of spectroscopic observations of HD45314 and HD60848, extending over 20 years. We further attempt to fit the H-alpha line profiles of both stars with a simple model of emission line formation in a Keplerian disk. Strong variations in the strengths of the H-alpha, H-beta, and He I 5876 emission lines are observed for both stars. In the case of HD60848, we find a time lag between the variations in the equivalent widths of these lines. The emission lines are double peaked with nearly identical strengths of the violet and red peaks. The H-alpha profile of this star can be successfully reproduced by our mod...

  12. Analysis of Kepler B stars: rotational modulation and Maia variables

    CERN Document Server

    Balona, L A; Daszynska-Daszkiewicz, J; De Cat, P

    2015-01-01

    We examine 4-yr almost continuous Kepler photometry of 115 B stars. We find that the light curves of 39 percent of these stars are simply described by a low-frequency sinusoid and its harmonic, usually with variable amplitudes, which we interpret as rotational modulation. A large fraction (28 percent) of B stars might be classified as ellipsoidal variables, but a statistical argument suggests that these are probably rotational variables as well. About 8 percent of the rotational variables have a peculiar periodogram feature which is common among A stars. The physical cause of this is very likely related to rotation. The presence of so many rotating variables indicates the presence of star spots. This suggests that magnetic fields are indeed generated in radiative stellar envelopes. We find five beta Cep variables, all of which have low frequencies with relatively large amplitudes. The presence of these frequencies is a puzzle. About half the stars with high frequencies are cooler than the red edge of the beta...

  13. Variable stars in the Globular Cluster NGC 2808

    CERN Document Server

    Kunder, Andrea; Catelan, Marcio; Walker, Alistair R; Amigo, Pia

    2012-01-01

    The first calibrated broadband BVI time-series photometry is presented for the variable stars in NGC 2808, with observations spanning a range of twenty-eight 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 \\sim0.8 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 _RR0=0.56 pm 0....

  14. C.Ragoonatha Chary and his Variable Stars

    CERN Document Server

    Rao, N Kameswara; Thakur, Priya; Birdie, Christina

    2009-01-01

    C. Ragoonatha Chary, the first assistant at Madras Observatory during 1864 to 1880 was not only a celebrated observational astronomer but also a person who emphasized the need for incorporating modern observations based improvements into the traditional methods of astronomical calculations. He was one of the first few people who argued for establishment of independent modern Indian observatory for education and training. He was credited with the discovery of two variable stars R Reticuli and another star whose identity is uncertain. The person and his variable star discoveries are discussed.

  15. Dynamical properties and search of variable stars: NGC 1960

    CERN Document Server

    Joshi, Gireesh C

    2015-01-01

    The total-to-selective extinction RV in the direction of a cluster is found to be 3.12 +/- 0.2 (close to its normal value). We derive the luminosity and mass functions for the cluster main sequence stars. The mass function slope is found to be -2.29 +/- 0.20 which is close to Salpeter value. We find evidence of mass segregation process in the cluster which is not yet dynamically relaxed. We have performed time series photometric observations to detect variable stars within star cluster NGC 1960. The DAOPHOT-II package is utilized to estimate the apparent stellar magnitudes of stars. The secondary standardization method is applied to the transformation of these apparent magnitudes into standard values. The magnitude-time diagrams (light curves) of stars are constructed to identify possible variability nature within them. The stars, having sufficient magnitude variation with time, are considered to be variable stars and their period values have computed through PERIOD04 package. These periodic values of variabl...

  16. Variable stars in the field of open cluster NGC 2126

    Institute of Scientific and Technical Information of China (English)

    Shun-Fang Liu; Zhen-Yu Wu; Xiao-Bin Zhang; Jiang-Hua Wu; Jun Ma; Zhao-Ji Jiang; Jian-Sheng Chen; Xu Zhou

    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 , age log(t)=8.95, distance modulus (m - M)0 = 10.34 and reddening value E(B -V) = 0.55 mag.

  17. The Bizarre Spectral Variability of Central Stars of Planetary Nebulae

    CERN Document Server

    De Marco, Orsola; Bond, Howard E; Harmer, Dianne

    2007-01-01

    A radial velocity (RV) survey to detect central stars in binary systems was carried out between 2002 and 2004. De Marco et al. (2004) reported that 10 out of 11 monitored stars exhibited strong RV variability, but periods were not detected. Since other mechanisms, such as wind variability, can cause apparent RV variations, we monitored 4 of the 10 RV-variable stars at echelle resolutions to determine the origin of the variability. Although RV changes are confirmed for all four stars, none of them can be ascribed to binarity at this time. However, only for IC4593 is wind variability able to explain most (though not all) spectral variability. For BD+332642, no wind and no pulsations appear to be the origin of the RV changes. Finally, M1-77 and M2-54, both known to be irregular photometric variables, exhibit dramatic RV and line shape variability of the hydrogen and HeI absorption lines, as well as large RV variability of weaker lines, which do not change in shape. There is no satisfactory explanation of this va...

  18. Trajectories of Cepheid variable stars in the Galactic nuclear bulge

    Science.gov (United States)

    Matsunaga, Noriyuki

    2012-06-01

    The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, ~10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, ~25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

  19. 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

    2002-01-01

    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 c

  20. Caroline Furness and the Evolution of Visual Variable Star Observing

    Science.gov (United States)

    Larsen, Kristine

    2017-01-01

    An Introduction to the Study of Variable Stars by Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, was published in October 2015. Issued in honor of the fiftieth anniversary of the founding of Vassar College, the work was meant to fill a void in the literature, namely as both an introduction to the topic of variable stars as well as a manual explaining how they should be observed and the resulting data analyzed. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World’s Fair in Chicago. The book covers the relevant history of and background on types of variable stars, star charts, catalogs, and the magnitude scale, then describes observing techniques, including visual, photographic, and photoelectric photometry. The work finishes with a discussion of light curves and patterns of variability, with a special emphasis on eclipsing binaries and long period variables. Furness’s work is therefore a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. Furness’s book and its reception in the scientific community are analyzed, and parallels with (and departures from) the current advice given by the AAVSO to beginning variable star observers today are highlighted.

  1. 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.

  2. Variable Star Status of Two Stars: V204 and I-I-39 in M3

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The star I-I-42 (=vZ1390), a cluster member in M3, located near the red edge of the instability strip of the horizontal branch, was discovered by Roberts and Sandage as a low amplitude variable, it was designated as V204 in the "second catalogue of variable stars in globular clusters", but its coordinates given in all versions of this catalogue are wrong since 1955. We argue that V204 is indeed a low amplitude HB variable star, located near to the red edge of the instability strip, with a period of 0.74785d and an amplitude of about 0.04 mag in V. We also find that the red cluster member star I-I-39 is a low amplitude variable with a period of 1.16d and amplitude of about 0.03 mag in V which might be pulsating at the second overtone.

  3. Observing variable stars at the University of Athens Observatory

    Science.gov (United States)

    Gazeas, K.; Manimanis, V. N.; Niarchos, P. G.

    In 1999 the University of Athens installed a 0.4-m Cassegrain telescope (CCT-16, by DFM Engineering) on the roof of the Department of Astrophysics, Astronomy and Mechanics, equipped with a ST-8 CCD camera and Bessel UBVRI filters. Although the telescope was built for educational purposes, we found it can be a perfect research instrument, as we can obtain fine quality light curves of bright variable stars, even from a place close to the city center. Light curves of the δ Scuti star V1162 Ori and of the sdB star PG 1336-018 are presented, showing the ability of a 40-cm telescope to detect negligible luminosity fluctuations of relatively bright variable stars. To date, we succeed in making photometry of stars down to 15th magnitude with satisfactory results. We expect to achieve even better results in the future, as our methods still improve, and as the large number of relatively bright stars gives us the chance to study various fields of CCD photometry of variables.

  4. Stellar variability in open clusters. I. A new class of variable stars in NGC 3766

    CERN Document Server

    Mowlavi, N; Saesen, S; Eyer, L

    2013-01-01

    Aims. We analyze the population of periodic variable stars in the open cluster NGC 3766 based on a 7-year multi-band monitoring campaign conducted on the 1.2 m Swiss Euler telescope at La Silla, Chili. Methods. The data reduction, light curve cleaning and period search procedures, combined with the long observation time line, allow us to detect variability amplitudes down to the milli-magnitude level. The variability properties are complemented with the positions in the color-magnitude and color-color diagrams to classify periodic variable stars into distinct variability types. Results. We find a large population (36 stars) of new variable stars between the red edge of slowly pulsating B (SPB) stars and the blue edge of delta Sct stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is predicted to occur based on standard stellar models. The bulk of their periods ranges from 0.1 to 0.7 d, with amplitudes between 1 and 4 mmag for the majority of them. About 20% of stars in that region of t...

  5. Terminal Cataclysm Epistemology: A Cataclysm that Never Happened?

    Science.gov (United States)

    Hartmann, W. K.

    2015-07-01

    The "terminal cataclysm" or "late heavy bombardment," concept of the last 40 years exhibits curious epistemology, with changing definitions and inconsistent evidence. A sharp "spike" in solar system basin formation at 3.9 Ga ago is untenable.

  6. Variable stars in the globular cluster NGC 2419

    CERN Document Server

    Greco, C; Federici, L; Clementini, G; Fabrizio, L D; Baldacci, L; Maio, M; Marconi, M; Musella, I; Stetson, P B

    2005-01-01

    We have used DOLORES at the TNG to obtain B,V time series photometry of NGC 2419, one of the most distant and bright clusters in the Galactic halo. These data will be used to study its variable star population in order to check whether the cluster could be the relic of an extragalactic system accreted by the Milky Way. Using the Image Subtraction technique (Alard 2000) we have identified about 300 candidate variables, many of which are in the cluster central regions. Several of the variables appear to be RR Lyrae stars, but we detected variability also around the tip of the red giant branch, and in other regions of the colour-magnitude diagram. To improve the light curve sampling and to resolve variables in the cluster inner regions, the TNG data were combined with HST archive data. Preliminary results are presented on the light curves from the combined data set.

  7. Variability and star formation in Leo T, the lowest luminosity star-forming galaxy known today

    CERN Document Server

    Clementini, Gisella; Ramos, Rodrigo Contreras; Federici, Luciana; Ripepi, Vincenzo; Marconi, Marcella; Tosi, Monica; Musella, Ilaria

    2012-01-01

    We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way (MW) "ultra-faint" dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 10 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409 $^{+29}_{-27}$ kpc (distance modulus of 23.06 $\\pm$ 0.15 mag) was derived from the galaxy's RR Lyrae star. Our V, V-I color-magnitude diagram of Leo T reaches V~29 mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the star formation history, based on the comparison of the observed V,V-I CMD...

  8. On the near infrared variability of chemically peculiar stars

    CERN Document Server

    Catalano, F A

    1998-01-01

    Some CP stars have recently been discovered by Catalano et al. (1991) to be variable also in the near infrared, although with smaller amplitudes than in the visible. Hence an observational campaign was started in which the infrared light variability of a number of CP2 and CP4 stars has been investigated at the ESO-La Silla Observatory in the bands J, H, and K. As a general result, infrared variations show the same behavior in all three filters but amplitudes are smaller than in the visible.

  9. Galactic and Extragalactic Distance Scales: The Variable Star Project

    CERN Document Server

    Feast, Michael W

    2008-01-01

    This paper summaries the status of a large project to improve distance scales of various classes of variable stars. This is being carried out by a large group in Cape Town, Japan, England and the USA. The results are illustrated by giving the distances of the Large Magellanic Cloud and the Galactic Centre (Ro) as well as the value of the Hubble Constant, Ho, based on our current results. The classes of variables considered are; Classical Cepheids, Type II Cepheids, RR Lyrae stars, O- and C-Miras

  10. Photometry of Variable Stars from Dome A, Antarctica

    CERN Document Server

    Wang, Lingzhi; Krisciunas, Kevin; Wang, Lifan; Ashley, Michael C B; Cui, Xiangqun; Feng, Long-Long; Gong, Xuefei; Lawrence, Jon S; Liu, Qiang; Luong-Van, Daniel; Pennypacker, Carl R; Shang, Zhaohui; Storey, John W V; Yang, Huigen; Yang, Ji; Yuan, Xiangyan; York, Donald G; Zhou, Xu; Zhu, Zhenxi

    2011-01-01

    Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night. We present high-cadence time-series aperture photometry of 10,000 stars with i<14.5 mag located in a 23 square-degree region centered on the south celestial pole. The photometry was obtained with one of the CSTAR telescopes during 128 days of the 2008 Antarctic winter. We used this photometric data set to derive site statistics for Dome A and to search for variable stars. Thanks to the nearly-uninterrupted synoptic coverage, we find 6 times as many variables as previous surveys with similar magnitude limits. We detected 157 variable stars, of which 55% are unclassified, 27% are likely binaries and 17% are likely pulsating stars. The latter category includes delta Scuti, gamma Doradus and RR Lyrae variables. One variable may be a transiting exoplanet.

  11. The Unusual Photometric Variability of the PMS Star GM Cep

    Science.gov (United States)

    Semkov, E. H.; Ibryamov, S. I.; Peneva, S. P.; Milanov, T. R.; Stoyanov, K. A.; Stateva, I. K.; Kjurkchieva, D. P.; Dimitrov, D. P.; Radeva, V. S.

    2015-03-01

    Results from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period 2011 April-2014 August are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (ΔV ~ 2.3 mag) and several deep minimums in brightness are observed. The analysis of the collected multicolour photometric data show the typical of UX Ori variables a colour reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for the classical T Tauri stars also present on the light curve of GM Cep. The spectrum of GM Cep shows the typical of classical T Tauri stars wide Hα emission line and absorption lines of some metals. We calculate the outer radius of the Hα emitting region as 10.4 ± 0.5 R⊙ and the accretion rate as 1.8 × 10- 7 M⊙ yr- 1.

  12. Measuring amplitudes of harmonics and combination frequencies in variable stars

    Science.gov (United States)

    Bellinger, E. P.; Wysocki, D.; Kanbur, S. M.

    2016-05-01

    Discoveries of RR Lyrae and Cepheid variable stars with multiple modes of pulsation have increased tremendously in recent years. The Fourier spectra of these stars can be quite complicated due to the large number of combination frequencies that can exist between their modes. As a result, light- curve fits to these stars often suffer from undesirable ringing effects that arise from noisy observations and poor phase coverage. These non-physical overfitting artifacts also occur when fitting the harmonics of single-mode stars. Here we present a new method for fitting light curves that is much more robust against these effects. We prove that the amplitude measurement problem is very difficult (NP-hard) and provide a heuristic algorithm for solving it quickly and accurately.

  13. Measuring amplitudes of harmonics and combination frequencies in variable stars

    CERN Document Server

    Bellinger, Earl P; Kanbur, Shashi M

    2015-01-01

    Discoveries of RR Lyrae and Cepheid variable stars with multiple modes of pulsation have increased tremendously in recent years. The Fourier spectra of these stars can be quite complicated due to the large number of combination frequencies that can exist between their modes. As a result, light-curve fits to these stars often suffer from undesirable ringing effects that arise from noisy observations and poor phase coverage. These non-physical overfitting artifacts also occur when fitting the harmonics of single-mode stars as well. Here we present a new method for fitting light curves that is much more robust against these effects. We prove that the amplitude measurement problem is very difficult (NP-hard) and provide a heuristic algorithm for solving it quickly and accurately.

  14. Nine New Variable Stars in Cygnus and Variability Type Determination of [Wm2007] 1176

    CERN Document Server

    Furgoni, Riccardo

    2014-01-01

    I report the discovery of nine new variable stars in Cygnus: five pulsating (VSX J192319.8+280832, VSX J192405.8+280352, VSX J192220.7+275518, VSX J192304.4+280231, VSX J192255.1+274744) and four eclipsing (VSX J192252.4+280217, VSX J192251.4+280456, VSX J192226.0+281019, VSX J192524.9+275342). The variability type of the variable star [WM2007] 1176, that was considered in literature a possible RRC, was found to be a W UMa variable with an obvious O'Connell effect.

  15. Variable stars in the bulge globular cluster NGC 6401

    CERN Document Server

    Tsapras, Y; Bramich, D M; Jaimes, R Figuera; Kains, N; Street, R; Hundertmark, M; Horne, K; Dominik, M; Snodgrass, C

    2016-01-01

    We present a study of variable stars in globular cluster NGC 6401. The cluster is only $5.3\\degr$ away from the Galactic centre and suffers from strong differential reddening. The photometric precision afforded us by difference image analysis resulted in improved sensitivity to variability in formerly inaccessible interior regions of the cluster. We find 23 RRab and 11 RRc stars within one cluster radius (2.4$\\arcmin$), for which we provide coordinates, finder-charts and time-series photometry. Through Fourier decomposition of the RR Lyrae star light curves we derive a mean metallicity of [Fe/H]$_{\\mathrm{UVES}} = -1.13 \\pm 0.06$ (${\\rm [Fe/H]}_{\\mathrm{ZW}} = -1.25 \\pm 0.06$), and a distance of $d\\approx 6.35 \\pm 0.81$ kpc. Using the RR Lyrae population, we also determine that NGC 6401 is an Oosterhoff type I cluster.

  16. K2 Variable Catalogue I: A Catalogue of Variable Stars from K2 Field 0

    CERN Document Server

    Armstrong, D J; Brown, D J A; Kirk, J; Lam, K W F; Pollacco, D L; Spake, J; Walker, S R

    2014-01-01

    We have searched the K2 campaign 0 data for lightcurve variations associated with stellar variability. The results of this search are presented as a catalogue, giving the identifiers of nearly 2500 variable stars in the dataset. We list the detected range of the variation, periodicity if relevant and semi-amplitude. Lightcurves are classified into strictly periodic, quasi-periodic and aperiodic groups. We do not attempt to identify the source of variability, which may arise from pulsation or stellar activity. However, we cross match the objects against variable star related guest observer proposals, specifying the variable type in many cases. At present eclipsing binary stars are not included. Future releases will address each K2 field as it is made available, and may be improved to include more detailed catalogue information and to provide detrended object lightcurves.

  17. Long-period variable stars in NGC 147 and NGC 185 - I. Their star formation histories

    Science.gov (United States)

    Hamedani Golshan, Roya; Javadi, Atefeh; van Loon, Jacco Th.; Khosroshahi, Habib; Saremi, Elham

    2017-04-01

    NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda galaxy (M 31). Close together in the sky, of similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? Here, we present the first reconstruction of the star formation histories of NGC 147 and NGC 185 using long-period variable stars. These represent the final phase of evolution of low- and intermediate-mass stars at the asymptotic giant branch, when their luminosity is related to their birth mass. Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC 185, we found that the main epoch of star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate. In the case of NGC 147, the star formation rate peaked only 7 Gyr ago, staying intense until ∼3 Gyr ago, but no star formation has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has evolved more slowly than NGC 185 initially, but more dramatically in more recent times. This is corroborated by the strong tidal distortions of NGC 147 and the presence of gas in the centre of NGC 185.

  18. 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.

  19. Variable stars in the Fornax dSph Galaxy. II. Pulsating stars below the horizontal branch

    CERN Document Server

    Poretti, Ennio; Held, Enrico V; Greco, Claudia; Mateo, Mario; Dell'Arciprete, Luca; Rizzi, Luca; Gullieuszik, Marco; Maio, Marcella

    2008-01-01

    We have carried out an intensive survey of the northern region of the Fornax dwarf spheroidal galaxy with the aim of detecting the galaxy's short--period pulsating stars (P<0.25 days). Observations collected over three consecutive nights with the Wide Field Imager of the 2.2m MPI telescope at ESO allowed us to detect 85 high-amplitude (0.20-1.00 mag in B-light) variable stars with periods in the range from 0.046 to 0.126 days, similar to SX Phoenicis stars in Galactic metal-poor stellar populations. The plots of the observed periods vs. the B and V magnitudes show a dispersion largely exceeding the observational errors. To disentangle the matter, we separated the first-overtone from the fundamental-mode pulsators and tentatively identified a group of subluminous variables, about 0.35 mag fainter than the others. Their nature as either metal-poor intermediate-age stars or stars formed by the merging of close binary systems is discussed. The rich sample of the Fornax variables also led us to reconstruct the ...

  20. Physical variability of the magnetic field of some stars

    CERN Document Server

    Bychkov, V D; Madej, J

    2016-01-01

    Apparent variability of the longitudinal magnetic fields in most stars is caused by rotation, which quantitavely changes projection of the magnetic field configuration on the line of sight. This is a purely geometrical effect and is not related to possible intrinsic changes of the field. In some stars we observe changes of the magnetic phase curve with time, which means that parameters of the magnetic field change. Such changes occur in some objects in time scale of several years, which is few orders of magnitude faster than predicted by theory. Those changes imply need for improvement of the theory of magnetic field evolution. We demonstrate changes of the rotational phase curves in few stars.

  1. Superhumps in Cataclysmic Binaries. XXV. q_crit, epsilon(q), and Mass-Radius

    CERN Document Server

    Patterson, J; Harvey, D; Fried, R; Rea, R; Monard, B; Cook, L; Skillman, D R; Vanmunster, T; Bolt, G; Armstrong, E; McCormick, J; Krajci, T; Jensen, L; Gunn, J; Butterworth, N D; Foote, J; Bos, M; Masi, G; Warhurst, P; Patterson, Joseph; Kemp, Jonathan; Harvey, David; Fried, Robert; Rea, Robert; Monard, Berto; Cook, Lewis; Skillman, David; Vanmunster, Tonny; Bolt, Greg; Armstrong, Eve; Cormick, Jennie Mc; Krajci, Thomas; Jensen, Lasse; Gunn, Jerry; Butterworth, Neil; Foote, Jerry; Bos, Marc; Masi, Gianluca; Warhurst, Paul

    2005-01-01

    We report on successes and failures in searching for positive superhumps in cataclysmic variables, and show the superhumping fraction as a function of orbital period. Basically, all short-period systems do, all long-period systems don't, and a 50% success rate is found at P_orb=3.1+-0.2 hr. We can use this to measure the critical mass ratio for the creation of superhumps. With a mass-radius relation appropriate for cataclysmic variables, and an assumed mean white-dwarf mass of 0.75 M_sol, we find a mass ratio q_crit=0.35+-0.02. We also report superhump studies of several stars of independently known mass ratio: OU Virginis, XZ Eridani, UU Aquarii, and KV UMa (= XTE J1118+480). The latter two are of special interest, because they represent the most extreme mass ratios for which accurate superhump measurements have been made. We use these to improve the epsilon(q) calibration, by which we can infer the elusive q from the easy-to-measure epsilon (the fractional period excess of P_superhump over P_orb). This rela...

  2. A Trip to the Cataclysmic Binary Zoo: Detailed Follow-Up of 35 Recently-Discovered Systems

    CERN Document Server

    Thorstensen, John R; Weil, Kathryn E

    2016-01-01

    We report follow-up studies of 35 recently-discovered cataclysmic variables (CVs), 32 of which were found in large, automated synoptic sky surveys. The objects were selected for observational tractability. For 34 of the objects we present mean spectra and spectroscopic orbital periods, and for one more we give an eclipse-based period. Thirty-two of the period determinations are new, and three of these refine published estimates based on superhump periods. The remaining three of our determinations confirm previously published periods. Twenty of the stars are confirmed or suspected dwarf novae with periods shorter than 3 hours, but we also find three apparent polars (AM Her stars), and six systems with P > 5 h, five of which have secondary stars visible in their spectra, from which we estimate distances when possible. The orbital period distribution of this sample is very similar to that of previously discovered CVs.

  3. Variable rotational line broadening in the Be star Achernar

    CERN Document Server

    Rivinius, Th; Townsend, R H D; Carciofi, A C; Štefl, S

    2013-01-01

    The main theoretical problem for the formation of a Keplerian disk around Be stars is how to supply angular momentum from the star to the disk, even more so since Be stars probably rotate somewhat sub-critically. For instance, nonradial pulsation may transport angular momentum to the stellar surface until (part of) this excess supports the disk formation/replenishment. The nearby Be star Achernar is presently building a new disk and offers an excellent opportunity to observe this process from relatively close-up. Spectra from various sources and epochs are scrutinized to identify the salient stellar parameters characterizing the disk life cycle as defined by H\\alpha emission. Variable strength of the non-radial pulsation is confirmed, but does not affect the further results. For the first time it is demonstrated that the photospheric line width does vary in a Be star, by as much as \\Delta v sin i \\lesssim 35kms^{-1}. However, contrary to assumptions in which a photospheric spin-up accumulates during the diskl...

  4. Random forest automated supervised classification of Hipparcos periodic variable stars

    Science.gov (United States)

    Dubath, P.; Rimoldini, L.; Süveges, M.; Blomme, J.; López, M.; Sarro, L. M.; De Ridder, J.; Cuypers, J.; Guy, L.; Lecoeur, I.; Nienartowicz, K.; Jan, A.; Beck, M.; Mowlavi, N.; De Cat, P.; Lebzelter, T.; Eyer, L.

    2011-07-01

    We present an evaluation of the performance of an automated classification of the Hipparcos periodic variable stars into 26 types. The sub-sample with the most reliable variability types available in the literature is used to train supervised algorithms to characterize the type dependencies on a number of attributes. The most useful attributes evaluated with the random forest methodology include, in decreasing order of importance, the period, the amplitude, the V-I colour index, the absolute magnitude, the residual around the folded light-curve model, the magnitude distribution skewness and the amplitude of the second harmonic of the Fourier series model relative to that of the fundamental frequency. Random forests and a multi-stage scheme involving Bayesian network and Gaussian mixture methods lead to statistically equivalent results. In standard 10-fold cross-validation (CV) experiments, the rate of correct classification is between 90 and 100 per cent, depending on the variability type. The main mis-classification cases, up to a rate of about 10 per cent, arise due to confusion between SPB and ACV blue variables and between eclipsing binaries, ellipsoidal variables and other variability types. Our training set and the predicted types for the other Hipparcos periodic stars are available online.

  5. A Variable Star Census in a Perseus Field

    CERN Document Server

    Pasternacki, T; Cabrera, J; Eigmueller, P; Erikson, A; Fruth, T; von Paris, P; Rauer, H; Titz, R; Eisloeffel, J; Hatzes, A; Boer, M; Tournois, G; Kabath, P; Hedelt, P; Voss, H; 10.1088/0004-6256/142/1/1

    2011-01-01

    The Berlin Exoplanet Search Telescope is a small-aperture, wide-field telescope dedicated to time-series photometric observations. During an initial commissioning phase at the Thueringer Landessternwarte Tautenburg, Germany, and subsequent operations at the Observatoire de Haute-Provence, France, a 3.1 {\\deg} x 3.1 {\\deg} circumpolar field close to the galactic plane centered at ({\\alpha}, {\\delta}) = (02h 39m 23s, +52{\\deg} 01' 46") (J 2000.0) was observed between 2001 August and 2006 December during 52 nights. From the 32129 stars observed, a subsample of 145 stars with clear stellar variability was detected out of which 125 are newly identified variable objects. For five bright objects, the system parameters were derived by modeling the light curve.

  6. Photometric Variability in Kepler Target Stars: The Sun Among Stars -- A First Look

    CERN Document Server

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

    2010-01-01

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

  7. The unusual photometric variability of the PMS star GM Cep

    CERN Document Server

    Semkov, E; Peneva, S; Milanov, T; Stoyanov, K; Stateva, I; Kjurkchieva, D; Dimitrov, D; Radeva, V

    2015-01-01

    Results from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period April 2011 - August 2014 are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (Delta V ~ 2.3 mag.) and several deep minimums in brightness are observed. The analysis of the collected multicolor photometric data shows the typical of UX Ori variables a color reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for th...

  8. Photometric variability of the Herbig Ae star HD 37806

    CERN Document Server

    Rucinski, S M; Hareter, M; Pojmanski, G; Kuschnig, R; Matthews, J M; Guenther, D B; Moffat, A F J; Sasselov, D; Weiss, W W

    2010-01-01

    The more massive counterparts of T Tauri stars, Herbig Ae/Be stars, are known to vary in a complex way with no variability mechanism clearly identified. We attempt to characterize the optical variability of HD~37806 (MWC 120) on time scales ranging between minutes and several years. A continuous, one-minute resolution, 21 day-long sequence of MOST (Microvariability & Oscillations of STars) satellite observations has been analyzed using wavelet, scalegram and dispersion analysis tools. The MOST data have been augmented by sparse observations over 9 seasons from ASAS (All Sky Automated Survey), by previously non-analyzed ESO (European Southern Observatory) data partly covering 3 seasons and by archival measurements dating back half a century ago. Mutually superimposed flares or accretion instabilities grow in size from about 0.0003 of the mean flux on a time scale of minutes to a peak-to-peak range of <~0.05 on a time scale of a few years. The resulting variability has properties of stochastic "red" nois...

  9. Highly variable young massive stars in ATLASGAL clumps

    CERN Document Server

    Kumar, M S N; Lucas, P W; Thompson, M A

    2016-01-01

    High-amplitude variability in Young Stellar Objects (YSOs) is usually associated with episodic accretion events. It has not been observed so far in massive YSOs. Here, the high-amplitude variable star sample of ContrerasPe\\~{n}a et al.(2016) has been used to search for highly-variable($\\Delta$K$\\ge$1\\,mag) sources coinciding with dense clumps mapped using the 850\\mum continuum emission by the ATLASGAL survey. 18 variable sources are centred on the sub-mm clump peaks, and coincide ($$2 mag, significantly higher compared to the mean variability of the entire VVV sample. The light curves of these objects sampled between 2010-2015 display rising, declining, or quasi-periodic behaviour but no clear periodicity. Light-curve analysis using Plavchan method show that the most prominent phased signals have periods of a few hundred days. The nature and time-scale of variations found in 6.7 Ghz methanol maser emission (MME) in massive stars are similar to that of the VYSO light curves. We argue that the origin of the obs...

  10. Long-term variability of T Tauri stars using WASP

    CERN Document Server

    Rigon, Laura; Anderson, David; West, Richard

    2016-01-01

    We present a reference study of the long-term optical variability of young stars using data from the WASP project. Our primary sample is a group of well-studied classical T Tauri stars (CTTS), mostly in Taurus-Auriga. WASP lightcurves cover timescales up to 7 years and typically contain 10000-30000 datapoints. We quantify the variability as function of timescale using the time-dependent standard deviation 'pooled sigma'. We find that the overwhelming majority of CTTS has low-level variability with sigma0.3mag) is 21% in our sample and 21% in an unbiased control sample. An even smaller fraction (13% in our sample, 6% in the control) show evidence for an increase in variability amplitude as a function of timescale from weeks to months or years. The presence of long-term variability correlates with the spectral slope at 3-5mu, which is an indicator of inner disk geometry, and with the U-B band slope, which is an accretion diagnostics. This shows that the long-term variations in CTTS are predominantly driven by p...

  11. Mixed-model Regression for Variable-star Photometry

    Science.gov (United States)

    Dose, Eric

    2016-05-01

    Mixed-model regression, a recent advance from social-science statistics, applies directly to reducing one night's photometric raw data, especially for variable stars in fields with multiple comparison stars. One regression model per filter/passband yields any or all of: transform values, extinction values, nightly zero-points, rapid zero-point fluctuations ("cirrus effect"), ensemble comparisons, vignette and gradient removal arising from incomplete flat-correction, check-star and target-star magnitudes, and specific indications of unusually large catalog magnitude errors. When images from several different fields of view are included, the models improve without complicating the calculations. The mixed-model approach is generally robust to outliers and missing data points, and it directly yields 14 diagnostic plots, used to monitor data set quality and/or residual systematic errors - these diagnostic plots may in fact turn out to be the prime advantage of this approach. Also presented is initial work on a split-annulus approach to sky background estimation, intended to address the sensitivity of photometric observations to noise within the sky-background annulus.

  12. A Package for the Automated Classification of Periodic Variable Stars

    CERN Document Server

    Kim, Dae-Won

    2015-01-01

    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 - Delta 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...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-02-01

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

  14. Rapid variability of OB-stars: nature and diagnostic value.

    Science.gov (United States)

    Baade, D.

    In the past decade, rapid photospheric variability has been recognized as the non-standard property that perhaps is the most common one among early-type stars. These proceedings offer an unusually complete overview of the existing observations. They are equally complete in their reflectance of the presently considered models. Because the simple definition 'on a rotational time scale' of the qualifier 'rapid' used in the title is very adequate for many stars, modulation is a strong contender also as a general model. The model that can be made to formally reproduce the widest range of observations is nonradial pulsation which, therefore, has earned itself the somewhat ambiguous reputation as a model for everything. An attraction of this model is that it would give the possibility to infer also structural and evolutionary quantities. It was the second purpose of the workshop to offer at least a glimpse of this potential.

  15. Variable Star Signature Classification using Slotted Symbolic Markov Modeling

    CERN Document Server

    Johnston, Kyle B

    2016-01-01

    With the advent of digital astronomy, new benefits and new challenges have been presented to the modern day astronomer. No longer can the astronomer rely on manual processing, instead the profession as a whole has begun to adopt more advanced computational means. This paper focuses on the construction and application of a novel time-domain signature extraction methodology and the development of a supporting supervised pattern classification algorithm for the identification of variable stars. A methodology for the reduction of stellar variable observations (time-domain data) into a novel feature space representation is introduced. The methodology presented will be referred to as Slotted Symbolic Markov Modeling (SSMM) and has a number of advantages which will be demonstrated to be beneficial; specifically to the supervised classification of stellar variables. It will be shown that the methodology outperformed a baseline standard methodology on a standardized set of stellar light curve data. The performance on ...

  16. Random forest automated supervised classification of Hipparcos periodic variable stars

    CERN Document Server

    Dubath, P; Süveges, M; Blomme, J; López, M; Sarro, L M; De Ridder, J; Cuypers, J; Guy, L; Lecoeur, I; Nienartowicz, K; Jan, A; Beck, M; Mowlavi, N; De Cat, P; Lebzelter, T; Eyer, L

    2011-01-01

    We present an evaluation of the performance of an automated classification of the Hipparcos periodic variable stars into 26 types. The sub-sample with the most reliable variability types available in the literature is used to train supervised algorithms to characterize the type dependencies on a number of attributes. The most useful attributes evaluated with the random forest methodology include, in decreasing order of importance, the period, the amplitude, the V-I colour index, the absolute magnitude, the residual around the folded light-curve model, the magnitude distribution skewness and the amplitude of the second harmonic of the Fourier series model relative to that of the fundamental frequency. Random forests and a multi-stage scheme involving Bayesian network and Gaussian mixture methods lead to statistically equivalent results. In standard 10-fold cross-validation experiments, the rate of correct classification is between 90 and 100%, depending on the variability type. The main mis-classification case...

  17. Data Mining Approach to Cataclysmic Variables Candidates Based on Random Forest Algorithm%基于随机森林的激变变星候选体的数据挖掘

    Institute of Scientific and Technical Information of China (English)

    姜斌; 罗阿理; 赵永恒

    2012-01-01

    提出一种适用于在郭守敬望远镜海量光谱中自动、快速筛选激变变星的方法.利用已证认的激变变星光谱作为模板,通过随机森林分类训练,得到一个分类模型,该模型给出了各个波长对应流量的重要性排序,可根据该排序进行降维并用于激变变星判别,结果作为反馈进一步丰富模板库.实验中共发现了16个新的激变变星候选体,表明了该方法的可行性.%An automatic and efficient method for cataclysmic variables candidates is presented in the present paper. The identified CVs were selected as templates. A model was constructed by random forest algorithm with templates and random selected spectra. Wavelength ranking was described by the model and the classifier was constructed afterwards. Most of the non-candidates were excluded by the method. Template matching strategy was used to identify the final candidates which were analyzed to complement the templates as feedback. 16 new CVs candidates were found in the experiment that shows that our approach to finding special celestial bodies can be feasible in LAMOST.

  18. 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

  19. John Goodricke, Edward Pigott, and Their Study of Variable Stars

    CERN Document Server

    French, L M

    2012-01-01

    John Goodricke and Edward Pigott, working in York, England, between 1781 and 1786, determined the periods of variation of eclipsing binaries such as Algol and Beta Lyrae and speculated that the eclipses of Algol might be caused by a "dark body," perhaps even a planet. They also determined the periods of variation of the first two known Cepheid variables, the stars whose period-luminosity relation today enables astronomers to determine distances to distant galaxies. Goodricke holds special interest because he was completely deaf and because he died at the age of 21. The lives and work of these two astronomers are described.

  20. Galactoseismology: Discovery of a cluster of receding, variable halo stars

    CERN Document Server

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

    2016-01-01

    A dynamical characterization of dark matter dominated dwarf galaxies from their observed effects on galactic disks (i.e. Galactoseismology) has remained an elusive goal. Here, we present preliminary results from spectroscopic observations of three clustered Cepheid candidates identified from $K$-band light curves towards Norma. The average heliocentric radial velocity of these stars is $\\sim$ 156 km/s, which is large and distinct from that of the Galaxy's stellar disk. These objects at $l \\sim 333 ^\\circ$ and $b \\sim -1 ^\\circ$ are therefore halo stars; using the $3.6~\\micron$ period-luminosity relation of Type I Cepheids, they are at $\\sim$ 73 kpc. Our ongoing $I$-band photometry indicates variability on the same time scale as the period determined from the $K_{s}$-band light curve. Distances determined from the $K$-band period-luminosity relation and the 3.6 $\\micron$ period-luminosity relation are comparable. The observed radial velocity of these stars agrees roughly with predictions from dynamical models....

  1. The star formation history of the Magellanic Clouds derived from long-period variable star counts

    CERN Document Server

    kh., Sara Rezaei; Khosroshahi, Habib; van Loon, Jacco Th

    2014-01-01

    We present the first reconstruction of the star formation history (SFH) of the Large and Small Magellanic Clouds (LMC and SMC) using Long Period Variable stars. These cool evolved stars reach their peak luminosity in the near-infrared; thus, their K-band magnitudes can be used to derive their birth mass and age, and hence the SFH can be obtained. In the LMC, we found a 10-Gyr old single star formation epoch at a rate of $\\sim1.5$ M$_\\odot$ yr$^{-1}$, followed by a relatively continuous SFR of $\\sim0.2$ M$_\\odot$ yr$^{-1}$, globally. In the core of the LMC (LMC bar), a secondary, distinct episode is seen, starting 3 Gyr ago and lasting until $\\sim0.5$ Gyr ago. In the SMC, two formation epochs are seen, one $\\sim6$ Gyr ago at a rate of $\\sim0.28$ M$_\\odot$ yr$^{-1}$ and another only $\\sim0.7$ Gyr ago at a rate of $\\sim0.3$ M$_\\odot$ yr$^{-1}$. The latter is also discernible in the LMC and may thus be linked to the interaction between the Magellanic Clouds and/or Milky Way, while the formation of the LMC bar may...

  2. A Comprehensive Review of Nova-Like Variable Stars

    Science.gov (United States)

    Sion, Edward

    2016-07-01

    A comprehensive review of nova-like variable stars of the VY Sculptoris and UX Ursa Majoris subtypes is presented. All that has been learned, up to the present time, from observations in the X-ray, far ultraviolet, optical and infrared bandpasses will be discussed. Spectroscopic analyses of high optical brightness states and low optical brightness states of nova-like variables will be summarized. The application of standard and non-standard accretion disk models as well as boundary layer structure will be discussed. The results of searches for nova shells, the evolutionary state of nova-likes as well as new spectroscopic results on BZ Cam (the bow shock CV) and BB Dor will also be included. This work is supported by NASA ADP grants NNX13AF12G and NNX13AF11G to Villanova University.

  3. The Self-Regulated Winds of Long Period Variable Stars

    CERN Document Server

    Struck, C; Willson, L A; Turner, G; Bowen, G H; Struck, Curtis; Smith, Daniel C.; Willson, Lee Anne; Turner, Gary; Bowen, George H.

    2004-01-01

    Numerical models of the extended atmospheres of long period variable or Mira stars have shown that their winds have a very simple, power law structure when averaged over the pulsation cycle. This structure is stable and robust despite the pulsational wave disturbances, and appears to be strongly self-regulated. Observational studies support these conclusions. The models also show that dust-free winds are nearly adiabatic, with little heating or cooling. The classical, steady, adiabatic wind solution to the hydrodynamic equations fails to account for an extensive region of nearly constant outflow velocity. We investigate analytic solutions which include the effects of wave pressure, heating, and the resulting entropy changes. Wave pressure is represented by a term like that in the Reynolds turbulence equation for the mean velocity. Although the pressure from individual waves is modest, the waves are likely the primary agent of self-regulation of dust-free winds. In models of dusty winds, the gas variables also...

  4. Mt. Suhora M dwarf survey - Detection of eight short-period variable stars

    CERN Document Server

    Machado, L Fox; Winiarski, M; Krzesiński, J; Dróżdz, M

    2011-01-01

    The Mt. Suhora M\\,dwarf survey searching for pulsations in low mass main sequence stars has acquired CCD photometry of 46 M\\,dwarf stars during the first year of the project (Baran et al 2011). As a by-product of this search hundreds field stars have been checked for variability. This paper presents our initial result of a search for periodic variables in field stars observed in the course of the survey. On the basis of the periodicity and the shape of the light curves, eight new variables has been detected, among which five are $\\delta$ Scuti stars and three likely RR Lyrae stars. Although variation in one of the stars has been previously detected, it was classified incorrectly. To support our classification, in August 2010, we performed spectroscopic observations to derive spectral types and luminosity classes for all eight variable stars.

  5. Short-term spectroscopic variability of Plaskett's star

    CERN Document Server

    Palate, Matthieu

    2014-01-01

    Context. Plaskett's star (HD47129) is a very massive O-star binary in a post Roche-lobe overflow stage. CoRoT observations of this system revealed photometric variability with a number of frequencies. Aims. The aim of this paper is to characterize the variations in spectroscopy and investigate their origin. Methods. To sample its short-term variability, HD47129 was intensively monitored during two spectroscopic campaigns of six nights each. The spectra were disentangled and Fourier analyses were performed to determine possible periodicities and to investigate the wavelength dependence of the phase constant and the amplitude of the periodicities. Results. Complex line profile variations are observed. Frequencies near 1.65, 0.82, and 0.37 d^-1 are detected consistently in the He i 4471, He ii 4542, and N iii 4510-4518 lines. These frequencies are consistent with those of the strongest signals detected in photometry. The possibilities that these variations stem from pulsations, a recently detected magnetic field...

  6. Confirming and Improving Ross Variable Star RV Del

    Science.gov (United States)

    Linder, Tyler R.; Sanchez, Rick; Palser, Sage; Schultze, Kendra; Kenney, Jessica; Thompson, Briana; DeCoster, Richard; Mills, Frank; Osborn, Wayne; Hoette, Vivian L.; Skynet Junior Scholars; Stone Edge Observatory

    2017-01-01

    RV Del is an intrinsic pulsating variable star in the constellation Delphinus, discovered by Ross (1926). The AAVSO list RV Del as a RRAB type of variable star. RV Del has been found to have a magnitude that varies from 12.9 - 14.2 and a period of 11.9553 hours.The purpose of our research of RV Del is to confirm and improve previous results as well as explore different methods to engage middle school students in the scientific method and astronomy. The SKYNET network of telescopes allows students to request images from a group of international research class telescopes. The telescope request process allows students first-hand experience in astronomy while the data analysis allows students to understand advance software systems to produce publishable results. Data is being gathered using the SKYNET network and Stone Edge Observatory to gather photometry of RV Del and create a new light curve. Findings will be presented the January 2017 AAS.

  7. Velocity structure in long period variable star atmospheres

    Science.gov (United States)

    Pilachowski, C.; Wallerstein, G.; Willson, L. A.

    1980-01-01

    A regression analysis of the dependence of absorption line velocities on wavelength, line strength, excitation potential, and ionization potential is presented. The method determines the region of formation of the absorption lines for a given data and wavelength region. It is concluded that the scatter which is frequently found in velocity measurements of absorption lines in long period variables is probably the result of a shock of moderate amplitude located in or near the reversing layer and that the frequently observed correlation of velocity with excitation and ionization are a result of the velocity gradients produced by this shock in the atmosphere. A simple interpretation of the signs of the coefficients of the regression analysis is presented in terms of preshock, post shock, or across the shock, together with criteria for evaluating the validity of the fit. The amplitude of the reversing layer shock is estimated from an analysis of a series of plates for four long period variable stars along with the most probable stellar velocity for these stars.

  8. Variability and pulsations in the Be star 66 Ophiuchi

    Science.gov (United States)

    Floquet, M.; Neiner, C.; Janot-Pacheco, E.; Hubert, A. M.; Jankov, S.; Zorec, J.; Briot, D.; Chauville, J.; Leister, N. V.; Percy, J. R.; Ballereau, D.; Bakos, A. G.

    2002-10-01

    66 Oph is a Be star seen under a moderate inclination angle that shows strong variability from UV to IR wavelengths. A concise review of long-term variability history is given. High resolution, high S/N spectroscopic observations obtained in 1997, 1998 and 2001 and spectropolarimetric observations obtained in 2000 are presented. These observations occurred during a long-term decrease of Hα intensity. Fundamental parameters of the star have been revisited from Barbier-Chalonge-Divan (BCD) calibrations. New V sin i values are obtained using Fourier transforms applied to observed helium lines and a rotational frequency f_rot = 1.29 c d-1 is determined. Time series analysis and Fourier Doppler Imaging (FDI) of He I lines (4713, 4921, 5876 and 6678 Å) lead for the first time to the detection of multi-periodicity in 66 Oph. The two main frequencies found are f = 2.22 c d-1 and f = 4.05 c d-1 . They are attributed to non-radial pulsations and can be associated with mode degree l = 2 and l = 3, respectively. Inspection of Stokes V profiles suggests the presence of a weak Zeeman signature but further observations are needed to confirm the detection of a magnetic field in 66 Oph. Based on observations taken at OHP and Pic du Midi Observatory (France), at MBT/LNA (Brazil) and on Brazilian observing time at La Silla (ESO, Chile).

  9. VX Her: Eclipsing Binary System or Single Variable Star

    Science.gov (United States)

    Perry, Kathleen; Castelaz, Michael; Henson, Gary; Boghozian, Andrew

    2015-01-01

    VX Her is a pulsating variable star with a period of .4556504 days. It is believed to be part of an eclipsing binary system (Fitch et al. 1966). This hypothesis originated from Fitch seeing VX Her's minimum point on its light curve reaching a 0.7 magnitude fainter than normal and remaining that way for nearly two hours. If VX Her were indeed a binary system, I would expect to see similar results with a fainter minimum and a broader, more horizontal dip. Having reduced and analyzed images from the Southeastern Association for Research in Astronomy Observatory in Chile and Kitt Peak, as well as images from a 0.15m reflector at East Tennessee State University, I found that VX Her has the standard light curve of the prototype variable star, RR Lyrae. Using photometry, I found no differing features in its light curve to suggest that it is indeed a binary system. However, more observations are needed in case VX Her is a wide binary.

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

    Science.gov (United States)

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

    2017-03-01

    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).

  11. The Quest for Identifying BY Draconis Stars within a Data Set of 3,548 Candidate Cepheid Variable Stars (Abstract)

    Science.gov (United States)

    Johnson, J.

    2016-06-01

    (Abstract only) A spreadsheet of 3,548 automatically classified candidate Cepheid variable stars from the ASAS (All Sky Automated Survey) photometry data was provided to AAVSO (American Association of Variable Star Observers) members for analysis. It was known that the computer filters had significantly overpopulated the list. Patrick Wils originally investigated a small subset of the data using 2MASS, PPMXL, and ROTSE data, and discovered that the vast majority of the 84 candidates he surveyed appeared to have been misidentified, demonstrating the need to reclassify these variables. The most common misidentification seemed to be of BY Draconis stars (K and M spotted dwarfs), which led to an ongoing project to systematically identify BY Draconis stars from this data set. The stars are sorted using the International Variable Star Index (VSX) information and ASAS light curves to search for prior reclassification by other authors in the time since the initial population of the candidate list (e.g. using ROTSE data), along with infrared photometry (2MASS) and proper motion (PPMXL) data. An analysis of light curves and phase plots using the AAVSO software vstar is the final step in identifying potential BY Draconis stars. The goal of this project has been to submit updated identifications for these stars to VSX. This final presentation on this project will identify the last set of reclassified BY Draconis stars and discuss future directions for this research.

  12. Utilizing the AAVSO's Variable Star Index (VSX) in Undergraduate Research Projects (Poster abstract)

    Science.gov (United States)

    Larsen, K.

    2016-12-01

    (Abstract only) Among the many important services that the American Association of Variable Star Observers (AAVSO) provides to the astronomical community is the Variable Star Index (VSX; https://www.aavso.org/vsx/). This online catalog of variable stars is the repository of data on over 334,000 variable stars, including information on spectral type, range of magnitude, period, and type of variable, among other properties. A number of these stars were identified as being variable through automated telescope surveys, such as ASAS (All Sky Automated Survey). The computer code of this survey classified newly discovered variables as best it could, but a significant number of false classifications have been noted. The reclassification of ASAS variables in the VSX data, as well as a closer look at variables identified as miscellaneous type in VSX, are two of many projects that can be undertaken by interested undergraduates. In doing so, students learn about the physical properties of various types of variable stars as well as statistical analysis and computer software, especially the vstar variable star data visualization and analysis tool that is available to the astronomical community free of charge on the AAVSO website (https://www.aavso.org/vstar-overview). Three such projects are described in this presentation, to identify BY Draconis variables misidentified as Cepheids or "miscellaneous", and SRD semiregular variables and ELL (rotating ellipsoidal) variables misidentified as "miscellaneous", in ASAS data and VSX.

  13. The Nature of Strange Modes in Classical Variable Stars

    CERN Document Server

    Buchler, J R; Kollath, Z

    1997-01-01

    Strange modes have been found in the radial spectrum of many luminous stars, most recently in Cepheids and RR Lyrae. We show that there is nothing strange about these modes -- they must exist even in the adiabatic limit. With a change of variables and without approximation the adiabatic linear pulsation equation is reduced to a Schroedinger equation in which the radial coordinate is the local sound-traversal time. In this formulation, the narrow hydrogen partial ionization region is seen to act as a potential barrier, separating the star into two regions. Resonances between the two regions result in the strange modes, for which the ratio of interior to exterior amplitude is at a minimum. The relative location of the barrier changes with the stellar parameters, and this gives rise to avoided level-crossings along a sequence of models. 2 The appearance of strange modes and the associated level crossings are exhibited with an analytic toy-model with the potential barrier approximated by a delta function. This to...

  14. Annual parallax measurements of a Mira variable star, U Lyncis

    Science.gov (United States)

    Kamezaki, Tatsuya; Nakagawa, Akiharu; Omodaka, Toshihiro; Handa, Toshihiro; Inoue, Kan-ichiro; Kurayama, Tomoharu; Kobayashi, Hideyuki; Nagayama, Takumi; Ueno, Yuji

    2016-10-01

    We have measured the annual parallax of the water maser around a Mira star, U Lyncis (U Lyn) with VLBI Exploration of Radio Astrometry (VERA). The value of the parallax is 1.27 ± 0.06 mas, corresponding to a distance of 786^{+40}_{-36}pc. This is the first VLBI measurement of the parallax of U Lyn. We obtained the period and the apparent magnitude of U Lyn based on near-infrared observations with the Kagoshima University 1 m telescope. The period and the mean magnitude of the K' band are 437.9 day and +1.15 ± 0.09 mag, respectively. Using our measured parallax and period, we find that the location of U Lyn on the period-luminosity plane is consistent with its nature as a Mira variable fundamental mode pulsator. Also, we estimated the distance using the period-luminosity relationship, our period and apparent magnitude and this gave a difference of about 100 pc between our parallactic distance and the distance estimated by using the period-luminosity relationship. We estimated the luminosity, radius, and mass of U Lyn to be 10100 ± 420 L⊙, 391 ± 34 R⊙, and 1.9 ± 0.7 M⊙, respectively. We found 50 water maser spots with a distribution ˜ 13 au around the star and the motion implies the existence of an outflow.

  15. Eruptive Variable Stars and Outflows in Serpens NW

    CERN Document Server

    Hodapp, Klaus W; Watermann, Ramon; Lemke, Roland

    2011-01-01

    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 broad-band K and in a narrow-band filter centered on the 1-0 S(1) emission line of molecular hydrogen 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 a molecular hydrogen jet emerging ...

  16. Variable Star Signature Classification using Slotted Symbolic Markov Modeling

    Science.gov (United States)

    Johnston, K. B.; Peter, A. M.

    2017-01-01

    With the advent of digital astronomy, new benefits and new challenges have been presented to the modern day astronomer. No longer can the astronomer rely on manual processing, instead the profession as a whole has begun to adopt more advanced computational means. This paper focuses on the construction and application of a novel time-domain signature extraction methodology and the development of a supporting supervised pattern classification algorithm for the identification of variable stars. A methodology for the reduction of stellar variable observations (time-domain data) into a novel feature space representation is introduced. The methodology presented will be referred to as Slotted Symbolic Markov Modeling (SSMM) and has a number of advantages which will be demonstrated to be beneficial; specifically to the supervised classification of stellar variables. It will be shown that the methodology outperformed a baseline standard methodology on a standardized set of stellar light curve data. The performance on a set of data derived from the LINEAR dataset will also be shown.

  17. Main-sequence variable stars in young open cluster NGC 1893

    OpenAIRE

    Lata, Sneh; Yadav, Ram Kesh; Pandey, A.K.(Indian Institute of Technology Bombay (IIT), Mumbai, India); Richichi, Andrea; Eswaraiah, C.; Kumar, Brajesh; Kappelmann, Norbert; Sharma, Saurabh

    2014-01-01

    In this paper we present time series photometry of 104 variable stars in the cluster region NGC 1893. The association of the present variable candidates to the cluster NGC 1893 has been determined by using $(U-B)/(B-V)$ and $(J-H)/(H-K)$ two colour diagrams, and $V/(V-I)$ colour magnitude diagram. Forty five stars are found to be main-sequence variables and these could be B-type variable stars associated with the cluster. We classified these objects as $\\beta$ Cep, slowly pulsating B stars an...

  18. Variable Stars as an Introduction to Computational Research

    Science.gov (United States)

    Cash, Jennifer; Walter, Donald K.

    2017-01-01

    As a part of larger effort to enhance the research activity at SC State and involve more undergraduates in research activities, we present our efforts to develop an introductory research experience where the goal is a balance of astrophysical understanding, general research skills, and programming skills which the students can carry into a wide variety of future research activities. We have found that variable stars are a very good topic for this sort of introductory experience due to a combination of factors including: accessibility of data, easily understandable physical processes, and a relatively straight forward data analysis process. We will present an outline of our research experiences to guide a student from the very initial stages of learning to final presentation of the student's work.“This work was supported in part by NSF PAARE award AST-1358913 and NSF HBCU-UP award HRD-1332449 to SCSU.”

  19. 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.

  20. Utilizing the AAVSO's Variable Star Index (VSX) In Undergraduate Research Projects

    Science.gov (United States)

    Larsen, Kristine

    2016-01-01

    Among the many important services that the American Association of Variable Star Observers (AAVSO) provides to the astronomical community is the Variable Star Index (VSX - https://www.aavso.org/vsx/). This online catalog of variable stars is the repository of data on over 334,000 variable stars, including information on spectral type, range of magnitude, period, and type of variable, among other properties. A number of these stars were identified as being variable through automated telescope surveys, such as ASAS (All Sky Automated Survey). The computer code of this survey classified newly discovered variables as best it could, but a significant number of false classifications have been noted. The reclassification of ASAS variables in the VSX data, as well as a closer look at variables identified as miscellaneous type in VSX, are two of many projects that can be undertaken by interested undergraduates. In doing so, students learn about the physical properties of various types of variable stars as well as statistical analysis and computer software, especially the VStar variable star data visualization and analysis tool that is available to the astronomical community free of charge on the AAVSO website (https://www.aavso.org/vstar-overview). Two such projects are described in this presentation, the first to identify BY Draconis variables erroneously classified as Cepheids in ASAS data, and the second to identify SRD semiregular variables misidentified as "miscellaneous" in VSX.

  1. 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.

  2. The TAOS Project Stellar Variability II. Detection of 15 Variable Stars

    Energy Technology Data Exchange (ETDEWEB)

    Mondal, S; Lin, C C; Zhang, Z W; Alcock, C; Axelrod, T; Bianco, F B; Byun, Y I; Coehlo, N K; Cook, K H; Dave, R; Kim, D W; King, S K; Lee, T; Lehner, M J; Lin, H C; Marshall, S L; Protopapas, P; Rice, J A; Schwamb, M E; Wang, J H; Wang, S Y; Wen, C Y

    2010-01-28

    The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data - covering timescales from a fraction of a second to a few hundred days - are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (RA = 17{sup h} 30{sup m} 6.67{sup s}, Dec = 27 degrees, 17 minutes, 30 seconds, J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 square degree field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the lightcurves, 32 variables, 18 of which were previously unknown, are classified as RR Lyrae, Cepheid, {delta} Scuti, SX Phonencis, semi-regular and eclipsing binaries.

  3. Accretion-disc model spectra for dwarf-nova stars

    OpenAIRE

    Idan, Irit; Lasota, Jean-Pierre; Hameury, Jean-Marie; Shaviv, Giora

    2008-01-01

    Radiation from accretion discs in cataclysmic variable stars (CVs) provides fundamental information about the properties of these close binary systems and about the physics of accretion in general. The detailed diagnostics of accretion disc structure can be achieved by including in its description all the relevant heating and cooling physical mechanism, in particular the convective energy transport that, although dominant at temperatures less than about 10 000 K, is usually not taken into acc...

  4. 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.

  5. Binary stars: Mass transfer and chemical composition

    Science.gov (United States)

    Lambert, D. L.

    1982-01-01

    It is noted that mass exchange (and mass loss) within a binary system should produce observable changes in the surface chemical composition of both the mass losing and mass gaining stars as a stellar interior exposed to nucleosyntheses is uncovered. Three topics relating mass exchange and/or mass loss to nucleosynthesis are sketched: the chemical composition of Algol systems; the accretion disk of a cataclysmic variable fed by mass from a dwarf secondary star; and the hypothesis that classical Ba II giants result from mass transfer from a more evolved companion now present as a white dwarf.

  6. The Identification of RR Lyrae and Delta Scuti Stars from Variable GALEX Ultraviolet Sources

    CERN Document Server

    Kinman, T D

    2014-01-01

    We identify the RR Lyrae and delta Scuti (DSCT) stars in three catalogs of GALEX variable sources. The NUV amplitude of RR Lyrae stars is about twice that in V-band, so we find a larger percentage of low amplitude variables than catalogs such as Abbas et al (2014). Interestingly, the (NUV-V)_0 color is sensitive to metallicity and can be used to distinguish between variables of the same period but differing [Fe/H]. This color is also more sensitive to T_eff than optical colors and can be used to identify the red edge of the instability gap. We find 8 DSCT stars, 17 RRc stars, 1 RRd star and 84 RRab stars in the GALEX variable catalogs of Welsh et al (2005) and Wheatley et al (2008). We also classify 6 DSCT stars, 5 RRc stars and 18 RRab stars among the 55 variable GALEX sources identified as "stars" or RR Lyraes in the catalog of Gezari et al (2013). We provide ephemerides and light curves for the 26 variables that were not previously known.

  7. Clustering-based Feature Learning on Variable Stars

    Science.gov (United States)

    Mackenzie, Cristóbal; Pichara, Karim; Protopapas, Pavlos

    2016-04-01

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

  8. Symbiotic stars in X-rays III: long term variability

    CERN Document Server

    Nuñez, N E; Mukai, K; Sokoloski, J L; Luna, G J M

    2015-01-01

    We study the X-ray emission from five symbiotic stars observed with Suzaku. These objects were selected for deeper observations with Suzaku after their first detection with ROSAT and Swift. We found that the X-ray spectra can be adequately fit with absorbed optically thin thermal plasma models, either single or multi-temperature. Such a model is compatible with the X-ray emission being originated in the innermost region of the accretion disk, i.e. a boundary layer. Based on the large flickering amplitude (only detected in 4 Dra), the high plasma temperature and previous measurements of UV variability and luminosity, we conclude that all five sources are accretion-powered through predominantly opticall thick boundary layer. Given the time lapse between previous and these observations, we were able to study the long term variability of their X-ray emission and found that the intrinsic X-ray flux and the intervening absorption column can vary by factors of three or more. However, it is still elusive the location...

  9. CLUSTERING-BASED FEATURE LEARNING ON VARIABLE STARS

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-04-01

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

  10. Variable Stars in the Quintuplet stellar sluster with the VVV Survey

    CERN Document Server

    Molina, C Navarro; Catelan, M; Alonso-García, J; Kerins, E; Kurtev, R; Lucas, P W; Medina, N; Minniti, D; Dékány, I

    2016-01-01

    The Quintuplet cluster is one of the most massive star clusters in the Milky Way, situated very close to the Galactic center. We present a new search for variable stars in the vicinity of the cluster, using the five-year database of the Vista Variables in the Via Lactea (VVV) ESO Public Survey in the near-infrared. A total of 7586 objects were identified in the zone around $2'$ from the cluster center, using 55 $K_S$-band epochs. Thirty-three stars show $K_S$-band variability, 24 of them being previously undiscovered. Most of the variable stars found are slow/semiregular variables, long-period variables of the Mira type, and OH/IR stars. In addition, a good number of our candidates show variations in a rather short timescale. We also propose four Young Stellar Object (YSO) candidates, which could be cluster members.

  11. Variable stars in the Quintuplet stellar cluster with the VVV survey

    Science.gov (United States)

    Navarro Molina, Claudio; Borissova, J.; Catelan, M.; Alonso-García, J.; Kerins, E.; Kurtev, R.; Lucas, P. W.; Medina, N.; Minniti, D.; Dékány, I.

    2016-10-01

    The Quintuplet cluster is one of the most massive star clusters in the Milky Way, situated very close to the Galactic Centre. We present a new search for variable stars in the vicinity of the cluster, using the five-year data base of the Vista Variables in the Via Lactea (VVV) ESO Public Survey in the near-infrared. A total of 7586 objects were identified in the zone around 2 arcmin from the cluster centre, using 55 KS-band epochs. 33 stars show KS-band variability, 24 of them being previously undiscovered. Most of the variable stars found are slow/semiregular variables, long-period variables of the Mira type, and OH/IR stars. In addition, a good number of our candidates show variations in a rather short time-scale. We also propose four young stellar object candidates, which could be cluster members.

  12. Searching for Line Profile Variability in HgMn Stars

    CERN Document Server

    Turcotte, S; Knoglinger, P

    2002-01-01

    Spectra of four non-magnetic chemically peculiar late B type stars (HgMn) stars are analysed to detect periodic spectral line variations (LPVs). A procedure developed to study LPVs in Slowly Pulsating B stars has been adopted as pulsational properties of HgMn stars should be expected to be similar. In the preliminary results discussed here no conclusive evidence for periodic LPVs was uncovered. A more sensitive re-analysis of the data is under way.

  13. Deep census of variable stars in a VLT/VIMOS field in Carina

    CERN Document Server

    Pietrukowicz, P; Fernández, J M; Pietrzynski, G; Ruiz, M T; Gieren, W; Diaz, R F; Zoccali, M; Hempel, M

    2009-01-01

    We have searched for variable stars in deep V-band images of a field towards the Galactic plane in Carina. The images were taken with VIMOS instrument at ESO VLT during 4 contiguous nights in April 2005. We detected 348 variables among 50897 stars in the magnitude range between V=15.4 and V=24.5 mag. Upon detection, we classified the variables by direct eye inspection of their light curves. All variable objects but 9 OGLE transits in the field are new discoveries. We provide a complete catalog of all variables which includes eclipsing/ellipsoidal binaries, miscellaneous pulsators (mostly delta Scuti-type variables), stars with flares and other (irregular and likely long-period) variables. Only two of the stars in our sample are known to host planets. Our result give some implications for future large variability surveys.

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

    Indian Academy of Sciences (India)

    Santosh Joshi

    2005-06-01

    The ``Nainital–Cape Survey” program for searching photometric variability in chemically peculiar (CP) stars was initiated in 1997 at ARIES, Nainital. We present here the results obtained to date. 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.

  15. On the new late B- and early A-type periodic variable stars

    CERN Document Server

    Mowlavi, Nami; Barblan, Fabio; Eyer, Laurent

    2013-01-01

    We summarize the properties of the new periodic, small amplitude, variable stars recently discovered in the open cluster NGC 3766. They are located in the region of the Hertzsprung-Russell diagram between \\delta\\ Sct and slowly pulsating B stars, a region where no sustained pulsation is predicted by standard models. The origin of their periodic variability is currently unknown. We also discuss how the Gaia mission, to be launched at the end of 2013, can contribute to our knowledge of those stars.

  16. Photometry of Variable Stars from THU-NAOC Transient Survey I: The First 2 Years

    CERN Document Server

    Yao, Xinyu; Wang, Xiaofeng; Zhang, Tianmeng; Chen, Juncheng; Yuan, Wenlong; Mo, Jun; Li, Wenxiong; Jin, Zhiping; Wu, Xuefeng; Nie, JunDan; Zhou, Xu

    2015-01-01

    In this paper, we report the detections of stellar variabilities from the first 2-year observations of sky area of about 1300 square degrees from the Tsinghua University-NAOC Transient Survey (TNTS). A total of 1237 variable stars (including 299 new ones) were detected with brightness = 0.1 mag on a timescale from a few hours to few hundred days. Among such detections, we tentatively identified 661 RR Lyrae stars, 431 binaries, 72 Semiregular pulsators, 29 Mira stars, 11 slow irregular variables, 11 RS Canum Venaticorum stars, 7 Gamma Doradus stars, 5 long period variables, 3 W Virginis stars, 3 Delta Scuti stars, 2 Anomalous Cepheids, 1 Cepheid, and 1 nove-like star based on their time-series variability index Js and their phased diagrams. Moreover, we found that 14 RR Lyrae stars show the Blazhko effect and 67 contact eclipsing binaries exhibit the O'Connell effect. Since the period and amplitude of light variations of RR Lyrae variables depend on their chemical compositions, their photometric observations ...

  17. Four New Delta Scuti Pulsators from a Variability Survey of 131 Stars

    CERN Document Server

    Sokoloski, J L; Chornock, R; Filippenko, A V; Bildsten, Lars; Filippenko, Alexei V.

    2002-01-01

    In a photometric variability survey of 131 stars with B < 14 mag, we have found four new Delta Scuti stars. We were sensitive to oscillation amplitudes as low as a few mmag. The detection rate of short-period (P < 0.1 d) pulsating variable stars, which may be relevant for planned large variability surveys such as GAIA, POI, and even the LSST, was therefore 3%. All four new variable stars have low pulsation amplitude (tens of mmag), and one has a very short period (0.0198 d). This star is one of the fastest known Delta Scuti pulsators. The short period of this variable star makes it observationally tractable, and it may therefore be a particularly good candidate for asteroseismological studies. All four new variable stars will add to the cadre of low-amplitude and relatively short-period Delta Scuti stars that are potentially useful for learning about the structure of stars on or near the main sequence, slightly more massive than the Sun.

  18. Are the stars of a new class of variability detected in NGC 3766 fast rotating SPB stars?

    Science.gov (United States)

    Salmon, S. J. A. J.; Montalbán, J.; Reese, D. R.; Dupret, M.-A.; Eggenberger, P.

    2015-01-01

    A recent photometric survey in the NGC 3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected, in between the δ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between ~0.1-0.7 d, are outside the expected domains of these well-known pulsators. The NCG 3766 cluster is known to host fast rotating stars. Rotation can significantly affect the pulsation properties of stars and alter their apparent luminosity through gravity darkening. Therefore we inspect if the new variable stars could correspond to fast rotating SPB stars. We carry out instability and visibility analysis of SPB pulsation modes within the frame of the traditional approximation. The effects of gravity darkening on typical SPB models are next studied. We find that at the red border of the SPB instability strip, prograde sectoral (PS) modes are preferentially excited, with periods shifted in the 0.2-0.5 d range due to the Coriolis effect. These modes are best seen when the star is seen equator-on. For such inclinations, low-mass SPB models can appear fainter due to gravity darkening and as if they were located between the δ Scuti and SPB instability strips.

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

    CERN Document Server

    Uytterhoeven, K; Grigahcene, A; Guzik, J A; Gutierrez-Soto, J; Smalley, B; Handler, G; Balona, L A; Niemczura, E; Machado, L Fox; Benatti, S; Chapellier, E; Tkachenko, A; Szabo, R; Suarez, J C; Ripepi, V; Pascual, J; Mathias, P; Martin-Ruiz, S; Lehmann, H; Jackiewicz, J; Hekker, S; Gruberbauer, M; Garcia, R A; Dumusque, X; Diaz-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

    The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. 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 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta 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 no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities...

  20. 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

    of NGC~6441, for which the variable star population of about 150 stars has been thoroughly examined by previous studies, including a Hubble Space Telescope study. In this paper we are able to present 49 new variable stars for this cluster, of which one (possibly two) are RR Lyrae stars, two are W...

  1. A Catalog of Eclipsing Binaries and Variable Stars Observed with ASTEP 400 from Dome C, Antarctica

    Science.gov (United States)

    Chapellier, E.; Mékarnia, D.; Abe, L.; Guillot, T.; Agabi, K.; Rivet, J.-P.; Schmider, F.-X.; Crouzet, N.; Aristidi, E.

    2016-10-01

    We used the large photometric database of the ASTEP program, whose primary goal was to detect exoplanets in the southern hemisphere from Antarctica, to search for eclipsing binaries (EcBs) and variable stars. 673 EcBs and 1166 variable stars were detected, including 31 previously known stars. The resulting online catalogs give the identification, the classification, the period, and the depth or semi-amplitude of each star. Data and light curves for each object are available at http://astep-vo.oca.eu.

  2. Are the stars of a new class of variability detected in NGC~3766 fast rotating SPB stars?

    CERN Document Server

    Salmon, S J A J; Reese, D R; Dupret, M -A; Eggenberger, P

    2014-01-01

    A recent photometric survey in the NGC~3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected, in between the $\\delta$ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between $\\sim$0.1--0.7~d, are outside the expected domains of these well-known pulsators. The NCG~3766 cluster is known to host fast rotating stars. Rotation can significantly affect the pulsation properties of stars and alter their apparent luminosity through gravity darkening. Therefore we inspect if the new variable stars could correspond to fast rotating SPB stars. We carry out instability and visibility analysis of SPB pulsation modes within the frame of the traditional approximation. The effects of gravity darkening on typical SPB models are next studied. We find that at the red border of the SPB instability strip, prograde sectoral (PS) modes are preferentially excited...

  3. FITDisk: Cataclysmic Variable Accretion Disk Demonstration Tool

    Science.gov (United States)

    Wood, Matthew A.; Dolence, J.

    2013-05-01

    FITDisk models accretion disk phenomena using a fully three-dimensional hydrodynamics calculation, and data can either be visualized as they are computed or stored to hard drive for later playback at a fast frame rate. Simulations are visualized using OpenGL graphics and the viewing angle can be changed interactively. Pseudo light curves of simulated systems can be plotted along with the associated Fourier amplitude spectrum. It provides an easy to use graphical user interface as well as 3-D interactive graphics. The code computes the evolution of a CV accretion disk, visualizes results in real time, records and plays back simulations, and generates and plots pseudo light curves and associated power spectra.

  4. 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.

  5. Kepler observations of the variability in B-type stars

    DEFF Research Database (Denmark)

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

    2011-01-01

    variations in other stars which we attribute to proximity effects in binary systems or possibly rotational modulation. We find no evidence for pulsating stars between the cool edge of the SPB and the hot edge of the δ Sct instability strips. None of the stars shows the broad features which can be attributed......The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could...... be considered as SPB/β Cephei (β Cep) hybrids. In all cases, the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree which are predicted to be unstable in models of mid-B stars. We find...

  6. RV variable, hot post-AGB stars from the MUCHFUSS project - Classification, atmospheric parameters, formation scenarios

    CERN Document Server

    Reindl, N; Kupfer, T; Bloemen, S; Schaffenroth, V; Heber, U; Barlow, B N; Østensen, R H

    2016-01-01

    In the course of the MUCHFUSS project we have recently discovered four radial velocity (RV) variable, hot (Teff $\\approx$ 80,000 - 110,000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV variable O(He) star, the only second known RV variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of an far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The "missing" PNe around the O(H)-type stars seem strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non...

  7. Exploring the variable stars in the globular cluster NGC5024 (M53): New RR Lyrae and SX Phoenicis stars

    CERN Document Server

    Ferro, A Arellano; Giridhar, Sunetra; Bramich, D M; Santisteban, J V Hernandez; Kuppuswamy, K

    2011-01-01

    We report CCD V and I time series photometry of the globular cluster NGC 5024 (M53). The technique of difference image analysis has been used which enables photometric precisions better than 10 mmag for stars brighter than V 18.5mag even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RR1 stars and thirteen SX Phe stars. A detailed identification chart is given for all the variable stars in the field of our images of the cluster. Periodicities were calculated for all RR Lyraes and SX Phe stars and a critical comparison is made with previous determinations. Out of four probable SX Phe variables reported by Dekany & Kovacs (2009), the SX Phe nature is confirmed only for V80, V81 is an unlikely case while V82 and V83 remain as dubious cases. Previous misidentifications of three variables are corrected. Astrometric positions with an uncertainty of ~ 0.3 arcsec are provided for all variables. The light curve Fourier decomposition of RR0 and...

  8. Image-Subtraction Photometry of Variable Stars in the Field of the Globular Cluster NGC 6934

    CERN Document Server

    Kaluzny, J; Stanek, K Z

    2001-01-01

    (Abriged) We present CCD BVI photometry of 85 variable stars from the field of the globular cluster NGC 6934. The photometry was obtained with the image subtraction package ISIS. 35 variables are new identifications: 24 RRab stars, 5 RRc stars, 2 eclipsing binaries of W UMa-type, one SX Phe star, and 3 variables of other types. Both detected contact binaries are foreground stars. The SX Phe variable belongs most likely to the group of cluster blue stragglers. Large number of newly found RR Lyr variables in this cluster, as well as in other clusters recently observed by us, indicates that total RR Lyr population identified up to date in nearby galactic globular clusters is significantly (>30%) incomplete. Fourier decomposition of the light curves of RRc variables was used to estimate the basic properties of these stars: M=0.63 M_odot, log(L/L_odot)=1.72, T_eff=7300 and Y=0.27. Using RRab variables we obtain: M_V=0.81, [Fe/H]=-1.53 and T_eff=6450. From the B-V color at minimum light of the RRab variables we obt...

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

    Science.gov (United States)

    Bowen, G. H.

    1989-01-01

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

  10. Multiband Fourier Analysis and Interstellar Reddening of Variable Stars in the Globular Cluster NGC 6584

    Science.gov (United States)

    Villiger, Nathan J.; Weinschenk, Sedrick; Hettinger, Paul T.; Murphy, Brian W.

    2017-01-01

    Globular clusters are excellent objects to study to help us understand the ways in which stars evolve. Key to this understanding are RR Lyrae variable stars. This research focused on the RR Lyrae stars in the globular cluster NGC 6584 to gain a better knowledge of post main sequence stellar evolution, horizontal branch morphology, and interstellar reddening to cluster variables. Using the 0.6 m SARA telescope at CTIO, we obtained nearly 1000 images in B, V, and I bands from July 2014 through July 2015. In addition to our prior work in V-band, this research adds B and I bands. By using difference image analysis, we found 77 variable stars in our 13’ x 13’ field of view. These consisted of 66 RR Lyrae stars, 7 long period variables, and 4 eclipsing binaries. The RR Lyrae stars were divided into 50 RR0 type stars, of which 14 exhibit the Blazhko effect, and 16 RR1 type stars. We found an average period for the RR0 variables of 0.56465 days and 0.30610 for the RR1 variables. By applying Fourier decomposition and examining the light curves in B, V, and I bands for each RR Lyrae variable, we were able to determine an average [Fe/H]JKZW of -1.619 ± 0.090, an average E(B-V) of 0.100 ± 0.032, and a distance to the cluster of 13527 ± 939 pc. This is the first detailed study to use RR Lyrae variable stars to estimate these parameters and the results are consistent with those obtained by other methods.

  11. Variability monitoring of OB stars during the Mons campaign

    CERN Document Server

    Morel, T; Eversberg, T; Alves, F; Arnold, W; Bergmann, T; Viegas, N G Correia; Fahed, R; Fernando, A; Carreira, L F Gouveia; Hunger, T; Knapen, J H; Leadbeater, R; Dias, F Marques; Moffat, A F J; Reinecke, N; Ribeiro, J; Romeo, N; Gallego, J Sanchez; Santos, E M dos; Schanne, L; Stahl, O; Stober, Ba; Stober, Be; Vollmann, K; Corcoran, M F; Dougherty, S M; Hamaguchi, K; Pittard, J M; Pollock, A M T; Williams, P M

    2010-01-01

    We present preliminary results of a 3-month campaign carried out in the framework of the Mons project, where time-resolved Halpha observations are used to study the wind and circumstellar properties of a number of OB stars.

  12. New Photometrically Variable Magnetic Chemically Peculiar Stars in the ASAS-3 Archive

    Science.gov (United States)

    Hümmerich, Stefan; Paunzen, Ernst; Bernhard, Klaus

    2016-10-01

    The magnetic Ap or CP2 stars are natural atomic and magnetic laboratories. Strictly periodic changes are observed in the spectra and brightness of these stars, which allow the derivation of rotational periods. Related to this group of objects are the He-weak (CP4) and He-rich stars, some of which also undergo brightness changes due to rotational modulation. Increasing the sample size of known rotational periods among CP2/4 stars is important and will contribute to our understanding of these objects and their evolution in time. We have compiled an extensive target list of CP2/4 stars from the General Catalog of Ap, HgMn, and Am stars, including several early-type (spectral types B/A) variables of undetermined type from the International Variable Star Index. We investigated our sample stars using publicly available observations from the ASAS-3 archive. Our previous efforts in this respect led to the discovery of 323 variable stars. Using a refined analysis approach, we were able to identify another 360 stars exhibiting photometric variability in ASAS-3 data. Summary data, folded light curves and, if available, information from the literature are presented for our final sample, which is composed of 334 bona-fide {α }2 Canum Venaticorum (ACV) variables, 23 ACV candidates, and 3 eclipsing binary systems. Interesting and unusual objects are discussed in detail. In particular, we call attention to HD 66051 (V414 Pup), which is an eclipsing binary system showing obvious rotational modulation of the light curve due to the presence of an ACV variable in the system.

  13. New Photometrically Variable Magnetic Chemically Peculiar Stars in the ASAS-3 Archive

    CERN Document Server

    Hümmerich, Stefan; Bernhard, Klaus

    2016-01-01

    The magnetic Ap or CP2 stars are natural atomic and magnetic laboratories and ideal testing grounds for the evaluation of model atmospheres. CP2 stars exhibiting photometric variability are traditionally referred to as alpha2 Canum Venaticorum (ACV) variables. Strictly periodic changes are observed in the spectra and brightness of these stars, which allow the derivation of rotational periods. Related to this group of objects are the He-weak (CP4) and He-rich stars, some of which are also known to undergo brightness changes due to rotational modulation. Increasing the sample size of known rotational periods among CP2/4 stars is an important task, which will contribute to our understanding of these objects and their evolution in time. We have compiled an extensive target list of magnetic chemically peculiar (CP2/4) stars. In addition to that, a systematic investigation of early-type (spectral types B/A) variable stars of undetermined type in the International Variable Star Index of the AAVSO (VSX) yielded addit...

  14. Relating jet structure to photometric variability: the Herbig Ae star HD 163296

    NARCIS (Netherlands)

    L.E. Ellerbroek; L. Podio; C. Dougados; S. Cabrit; M.L. Sitko; H. Sana; L. Kaper; A. de Koter; P.D. Klaassen; G.D. Mulders; I. Mendigutía; C.A. Grady; K. Grankin; H. van Winckel; F. Bacciotti; R.W. Russell; D.K. Lynch; H.B. Hammel; L.C. Beerman; A.N. Day; D.M. Huelsman; C. Werren; A. Henden; J. Grindlay

    2014-01-01

    Herbig Ae/Be stars are intermediate-mass pre-main sequence stars surrounded by circumstellar dust disks. Some are observed to produce jets, whose appearance as a sequence of shock fronts (knots) suggests a past episodic outflow variability. This "jet fossil record" can be used to reconstruct the out

  15. 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

    observational instability strips. The hybrid stars occupy the entire region within the δ Sct and γ Dor instability strips and beyond. Non-variable stars seem to exist within the instability strips. The location of γ Dor and δ Sct classes in the (Teff, log g)-diagram has been extended. We investigate two newly...

  16. VARIABLE-STARS IN THE IRREGULAR GALAXY NGC-2366 (DDO-42)

    NARCIS (Netherlands)

    TOLSTOY, E; SAHA, A; HOESSEL, JG; MCQUADE, K

    1995-01-01

    Observations of the resolved stars in the Irregular galaxy NGC 2366, obtained over the ten year period from March 1984 to March 1994, are presented. Thirty separate epochs were used to search for variable stars, and a total of 13 were found, of which 6 have characteristic Cepheid light curves and co

  17. 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.

  18. The MACHO Project LMC Variable Star Inventory; 4, Multimode RR Lyrae Stars, Distance to the LMC and Age of the Oldest Stars

    CERN Document Server

    Alcock, C B; Alves, D R; Axelrod, T S; Becker, A C; Bennett, D P; Cook, K H; Freeman, K C; Griest, K; Guern, J A; Lehner, M J; Marshall, S L; Minniti, D; Peterson, B A; Pratt, M R; Quinn, P J; Rodgers, A W; Sutherland, W; Welch, D L

    1996-01-01

    We report the discovery of 73 double-mode RR Lyrae (RRd) stars in fields near the bar of the LMC. The stars are detected among the MACHO database of short-period variables that currently contains about 7900 RR Lyrae stars. Fundamental periods (P_0) for these stars are found in the range 0.46-0.55 days and first overtone-to-fundamental period ratios are found to be in the range 0.742 < P_1/P_0 < 0.748. A significant fraction of our current sample have period ratios smaller than any previously discovered RRd variables. We present mean magnitudes, colors, and lightcurve properties for all LMC RRd stars detected to date. The range in period ratios is unexpectedly large. We present a determination of absolute magnitudes for these stars based primarily on pulsation theory and the assumption that all observed stars are at the fundamental blue edge (FBE) of the instability strip. Comparison of the calibrated MACHO V and R_KC photometry with these derived absolute magnitudes yields an absorption-corrected distan...

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

    Science.gov (United States)

    Wang, Lingzhi; Ma, Bin; Li, Gang; Hu, Yi; Fu, Jianning; Wang, Lifan; Ashley, Michael C. B.; Cui, Xiangqun; Du, Fujia; Gong, Xuefei; Li, Xiaoyan; Li, Zhengyang; Liu, Qiang; Pennypacker, Carl R.; Shang, Zhaohui; Yuan, Xiangyan; York, Donald G.; Zhou, Jilin

    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.

  20. Amplitude Variability in gamma Dor and delta Scuti stars observed by the Kepler Spacecraft

    CERN Document Server

    Guzik, Joyce A; Bradley, Paul A; Jackiewicz, Jason

    2016-01-01

    The NASA Kepler spacecraft data revealed a large number of multimode nonradially pulsating gamma Dor and delta Sct variable star candidates. The high precision long time-series photometry makes it possible to study amplitude variations of the frequencies. We summarize recent literature on amplitude and frequency variations in pulsating variables. We are searching for amplitude variability in several dozen faint gamma Doradus or delta Scuti variable-star candidates observed as part of the Kepler Guest Observer program. We apply several methods, including a Matlab-script wavelet analysis developed by J. Jackiewicz, and the wavelet technique of the VSTAR software (http://www.aavso.org/vstar-overview). Here we show results for two stars, KIC 2167444 and KIC 2301163. We discuss the magnitude and timescale of the amplitude variations, and the presence or absence of correlations between amplitude variations for different frequencies of a given star. Amplitude variations may be detectable using Kepler data even for s...

  1. New variables in M5 (NGC 5904) and some identification corrections

    CERN Document Server

    Ferro, A Arellano; Giridhar, S; Luna, A; Muneer, S

    2015-01-01

    We report twelve variables not previously detected in the globular cluster M5 (NGC 5904); one SX Phe and eleven semi-regular variables (SR). Their identifications, equatorial coordinates, ephemerides, and light curves are given. Furthermore, we have explored the light curves of a group of stars whose variability has not been confirmed and that are marked as probable non- variables in the CVSGC. Finally, we offer detailed identifications for some of the known variables in crowded regions that were misidentified in previous studies. We shall also address the cases of the cataclysmic variable or U Gem type V101 and of the variable blue straggler V159.

  2. Automated Classification of Periodic Variable Stars detected by the Wide-field Infrared Survey Explorer

    CERN Document Server

    Masci, Frank J; Grillmair, Carl J; Cutri, Roc M

    2014-01-01

    We describe a methodology to classify periodic variable stars identified in the Wide-field Infrared Survey Explorer (WISE) full-mission single-exposure Source Database. This will assist in the future construction of a WISE periodic-Variable Source Database that assigns variables to specific science classes as constrained by the WISE observing cadence with statistically meaningful classification probabilities. We have analyzed the WISE light curves of 8273 variable stars identified in previous optical variability surveys (MACHO, GCVS, and ASAS) and show that Fourier decomposition techniques can be extended into the mid-IR to assist with their classification. Combined with other periodic light-curve features, this sample is then used to train a machine-learned classifier based on the random forest (RF) method. Consistent with previous classification studies of variable stars in general, the RF machine-learned classifier is superior to other methods in terms of accuracy, robustness against outliers, and relative...

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

    Science.gov (United States)

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

    2014-02-01

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

  4. Charles Lewis Brook: third Director of the BAA Variable Star Section

    CERN Document Server

    Shears, Jeremy

    2011-01-01

    Charles Lewis Brook, MA, FRAS, FRMetS (1855 - 1939) served as Director of the BAA Variable Star Section from 1910 to 1921. During this time he was not merely interested in collecting the observations of the members (to which he also contributed), but he also spent considerable amounts of time analysing the data and preparing numerous publications on the findings. This paper discusses Brook's life and work, with a particular focus on his contribution to variable star astronomy.

  5. To Pulsate or to Eclipse? Status of KIC 9832227 Variable Star

    OpenAIRE

    2013-01-01

    The variable star known as NSVS 5597754 was identified as a short period RRc field star from ground-based photometry. This star happens to fall in the Kepler field of view and has been observed for 3 years with the Kepler spacecraft. Renamed KIC 9832227, this star was reidentified as an eclipsing binary with a periodicity of 0.457970 days. The NSVS ground based photometry yielded a period solution of 0.229 days. The Kepler photometry, which sampled the light cycle every 30 minutes, shows a pe...

  6. Star Wreck

    OpenAIRE

    Kusenko, Alexander; Shaposhnikov, Mikhail E.; Tinyakov, P. G.; 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 or...

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

    CERN Document Server

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

    2016-01-01

    We present the identification of 634 variable stars in the Milky Way dSph satellite Sculptor based on archival ground-based optical observations spanning $\\sim$24 years and covering $\\sim$ 2.5 deg$^2$. We employed the same methodologies as the "Homogeneous Photometry" series published by Stetson. In particular, we have identified and characterized the largest (536) RR Lyrae sample 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 \\textit{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 ...

  8. A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

    Science.gov (United States)

    Bernhard, K.; Hümmerich, S.; Otero, S.; Paunzen, E.

    2015-09-01

    Context. The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as α2 Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. An increased sample size will contribute to the understanding of the CP stars' evolution in time. Aims: We aim at discovering new ACV variables in the public data of the third phase of the All Sky Automated Survey (ASAS-3). Furthermore, by analysis of the available photometric data, we intend to derive rotational periods of the stars. Methods: The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. Objects exhibiting periodic signals well above the noise level were considered and visually inspected, whereas borderline cases were rejected. Results: In total, we found 323 variables, from which 246 are reported here for the first time, and 77 were probably wrongly classified before. The observed variability pattern of most stars is in accordance with an ACV classification. For some cases, it is difficult to distinguish between the light curves of double-waved ACVs and the variability induced by orbital motion (ellipsoidal variables/eclipsing variables), especially for objects exhibiting very small amplitudes and/or significant scatter

  9. Variable stars in the bar of the Large Magellanic Cloud: the photometric catalogue

    CERN Document Server

    Fabrizio, L D; Maio, M; Bragaglia, A; Carretta, E; Gratton, R; Montegriffo, P; Zoccali, M

    2004-01-01

    The catalogue of the Johnson-Cousins B,V and I light curves obtained for 162 variable stars (135 RR Lyrae, 4 candidate Anomalous Cepheids, 11 Classical Cepheids, 11 eclipsing binaries and 1 delta Scuti star) in two areas close to the bar of the Large Magellanic Cloud is presented along with coordinates, finding charts, periods, epochs, amplitudes, and mean quantities (intensity- and magnitude-averaged luminosities) of the variables with full coverage of the light variations. A star by star comparison is made with MACHO and OGLE II photometries based on both variable and constant stars in common, and the transformation relationships to our photometry are provided. The pulsation properties of the RR Lyrae stars in the sample are discussed in detail. Parameters of the Fourier decomposition of the light curves are derived for the fundamental mode RR Lyrae stars with complete and regular curves (29 stars). They are used to estimate metallicities, absolute magnitudes, intrinsic (B-V)o colours, and temperatures of t...

  10. Square root two period ratios in Cepheid and RR Lyrae variable stars

    CERN Document Server

    Hippke, Michael; Zee, A

    2014-01-01

    We document the presence of nine Cepheid and RR Lyrae variable stars with previously unrecognized characteristics. These stars exhibit the statistically unlikely property of a period ratio of main pulsation divided by secondary pulsation (P1/P2) very close to sqrt(2). Other stars of these types have period ratios which show clustering not with a close association with a single remarkable and nonharmonic number. In the way of explanation, we suggest that this indicates a previously unknown resonance of pulsations. Close examination reveals a deviation of multiples of a few times 0.06% for these stars. This deviation seems to be present in discrete steps on the order of about 0.000388(5), indicating the possible presence of a sort of fine structure in this oscillation. Physical explanation of the source of these regularities remains for 3D simulations of variable stars, and we only claim to make note of the regularities which are suggestive of physical principles.

  11. Variable Stars in the Cetus dSph Galaxy: Population Gradients and Connections with the Star Formation History

    CERN Document Server

    Monelli, M; Gallart, C; Fiorentino, G; Drozdovsky, I; Aparicio, A; Bono, G; Cassisi, S; Skillman, E D; Stetson, P B

    2012-01-01

    We investigate the variable star content of the isolated, Local Group, dwarf spheroidal galaxy (dSph) Cetus. Multi-epoch, wide-field images collected with the VLT/VIMOS camera allowed us to detect 638 variable stars (630 RR Lyrae stars and 8 Anomalous Cepheids), 475 of which are new detections. We present a full catalogue of periods, amplitudes, and mean magnitudes. Motivated by the recent discovery that the pulsational properties of the RR Lyrae stars in the Tucana dSph revealed the presence of a metallicity gradient within the oldest (>10 Gyr old) stellar populations, we investigated the possibility of an analogous effect in Cetus. We found that, despite the obvious radial gradient in the Horizontal Branch (HB) and Red Giant Branch (RGB) morphologies, both becoming bluer on average for increasing distance from the center of Cetus, the properties of the RR Lyrae stars are homogeneous within the investigated area (out to r~15'), with no significant evidence of a radial gradient. We discuss this in connection ...

  12. Investigating Variability of Quiescent Neutron Stars in the Globular Clusters NGC 6440 and Terzan 5

    CERN Document Server

    Walsh, A R; Bernardini, F

    2014-01-01

    The quiescent spectrum of neutron star low-mass X-ray binaries typically consists of two components - a thermal component associated with emission from the neutron star surface, and a non-thermal power-law component whose origin is not well understood. Spectral fitting of neutron star atmosphere models to the thermal component is one of the leading methods for measuring the neutron star radius. However, it has been known for years that the X-ray spectra of quiescent neutron stars vary between observations. While most quiescent variability is explained through a variable power-law component, the brightest and best-studied object, Cen X-4, requires a change in the thermal component and such thermal variability could be a problem for measuring neutron star radii. In this paper, we significantly increase the number of sources whose quiescent spectra have been studied for variability. We examine 9 potential quiescent neutron stars with luminosities <1E34 erg/s over the course of multiple Chandra observations of...

  13. The nature of the light variability of magnetic Of?p star HD 191612

    Science.gov (United States)

    Krtička, J.

    2016-10-01

    Context. A small fraction of hot OBA stars host global magnetic fields with field strengths of the order of 0.1-10 kG. This leads to the creation of persistent surface structures (spots) in stars with sufficiently weak winds as a result of the radiative diffusion. These spots become evident in spectroscopic and photometric variability. This type of variability is not expected in stars with strong winds, where the wind inhibits the radiative diffusion. Therefore, a weak photometric variability of the magnetic Of?p star HD 191612 is attributed to the light absorption in the circumstellar clouds. Aims: We study the nature of the photometric variability of HD 191612. We assume that the variability results from variable wind blanketing induced by surface variations of the magnetic field tilt and modulated by stellar rotation. Methods: We used our global kinetic equilibrium (NLTE) wind models with radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the stellar emergent flux. Our models describe the stellar atmosphere in a unified manner and account for the influence of the wind on the atmosphere. The models are calculated for different wind mass-loss rates to mimic the effect of magnetic field tilt on the emergent fluxes. We integrate the emergent fluxes over the visible stellar surface for individual rotational phases, and calculate the rotationally modulated light curve of HD 191612. Results: The wind blanketing that varies across surface of HD 191612 is able to explain a part of the observed light variability in this star. The mechanism is able to operate even at relatively low mass-loss rates. The remaining variability is most likely caused by the flux absorption in circumstellar clouds. Conclusions: The variable wind blanketing is an additional source of the light variability in massive stars. The presence of the rotational light variability may serve as a proxy for the magnetic field.

  14. 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.

  15. Stellar Variability of the Exoplanet Hosting Star HD 63454

    CERN Document Server

    Kane, Stephen R; Ciardi, David R; Lee, Jae-Woo; Curto, Gaspare Lo; Lovis, Christophe; Naef, Dominique; Mahadevan, Suvrath; Pilyavsky, Genady; Udry, Stephane; Wang, Xuesong; Wright, Jason

    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 for stellar activity both intrinsic to the star and induced by possible interactions of the exoplanet with the stellar magnetospheres. We establish the photometric stability of the star at the 3 millimag level despite strong Ca II emission in the spectrum. Finally, we rule out photometric signatures of both star-planet magnetosphere interactions and planetary transit signatures. From this we are able to place constraints on both the orbital and physical properties of the planet.

  16. The composition of HB stars RR Lyrae variables

    CERN Document Server

    Clementini, G; Gratton, R G; Merighi, R; Mould, J R; McCarthy, J K

    1995-01-01

    We used moderately high-resolution, high S/N spectra to study the chemical composition of 10 field ab-type RR Lyrae stars. A new temperature scale was determined from literature Infrared Flux Method measures of subdwarfs and the Kurucz (1992) model atmospheres, and used to calibrate colors for both dwarfs and RR Lyraes. The applicability of Kurucz (1992) model atmospheres in the analysis of RR Lyraes at minimum light was analyzed: we found that they are able to reproduce colors, excitation and ionization equilibria as well as the wings of Halpha. We derived abundances for 21 species. The metal abundances of the program stars span the range -2.50<[Fe/H]<+0.17. Lines of most elements are found to form in LTE conditions. Fe lines satisfy very well the excitation and ionization equilibria. RR Lyraes share the typical abundance pattern of other stars of similar [Fe/H]: alpha-elements are overabundant by about 0.4dex and Mn is underabundant by about 0.6dex in stars with [Fe/H]<-1. Significant departures fr...

  17. Study of variable stars in the MOA data base long-period red variables in the Large Magellanic Cloud

    CERN Document Server

    Noda, S; Abe, F; Bond, I A; Dodd, R J; Hearnshaw, J B; Honda, M; Honma, M; Juga Ku Jun; Kabe, S; Kan-Ya, Y; Kato, Y; Kilmartin, P M; Matsubara, Y; Masuda, K; Muraki, Y; Nakamura, T; Nankivell, G R; Noguchi, C; Ohnishi, K; Reid, M; Rattenbury, N J; Saitô, T; Sato, H; Sekiguchi, M; Skuljan, J; Sullivan, D J; Sumi, T; Watase, Y; Wilkinson, S; Yamada, R; Yanagisawa, T; Yock, P C M; Yoshizawa, M; Saito, To.

    2002-01-01

    One hundred and forty six long-period red variable stars in the Large Magellanic Cloud (LMC) from the three year MOA project database were analysed. A careful periodic analysis was performed on these stars and a catalogue of their magnitudes, colours, periods and amplitudes is presented. We convert our blue and red magnitudes to $K$ band values using 19 oxygen-rich stars. A group of red short-period stars separated from the Mira sequence has been found on a (log P, K) diagram. They are located at the short period side of the Mira sequence consistent with the work of Wood and Sebo (1996). There are two interpretations for such stars; a difference in pulsation mode or a difference in chemical composition. We investigated the properties of these stars together with their colour, amplitude and periodicity. We conclude that they have small amplitudes and less regular variability. They are likely to be higher mode pulsators. A large scatter has been also found on the long period side of the (log P, K) diagram. This...

  18. Variable Stars in the Field of the Open Cluster NGC 2126

    CERN Document Server

    Liu, Shun-Fang; Zhang, Xiao-Bin; Wu, Jiang-Hua; Ma, Jun; Jiang, Zhao-Ji; Chen, Jian-Sheng; Zhou, Xu

    2009-01-01

    We report the results of a time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2126. In about one square degree field covering the cluster, a total number 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 binaries systems, three pulsating variable stars, three long period variables, one RS CVn star, and one W UMa or $\\delta$ Scuti star. In addition, there are two variable candidates, the properties of which cannot be determined in this paper. By a method based on fitting spectral energy distributions(SEDs) 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 the this cluster are determined as: the metallicity to be 0.008 $Z_\\odot$, the age $\\log(t)$=...

  19. Constraining the Variability and Binary Fraction of Galactic Center Young Stars

    CERN Document Server

    Gautam, Abhimat K; Ghez, Andrea M; Lu, Jessica R; Morris, Mark R; Sakai, Shoko; Witzel, Gunther; Sitarski, Breann N; Chappell, Samantha

    2016-01-01

    We present constraints on the variability and binarity of young stars in the central 10 arcseconds (~0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment's photometric uncertainties, at least 36% of our sample's known early-type stars are variable. We identified eclipsing binary systems by searching for periodic variability. In our sample of spectroscopically confirmed and likely early-type stars, we detected the two previously discovered GC eclipsing binary systems. We derived the likely binary fraction of main sequence, early-type stars at the GC via Monte Carlo simulations of eclipsing binary systems, and find that it is at least 32% with 90% confidence.

  20. Variable stars observed with the AST3-1 telescope from dome A of antarctica

    CERN Document Server

    Li, Gang; Liu, Xuanming

    2015-01-01

    Dome A in the Antarctic plateau is likely one of the best astronomical observing sites on Earth. The first one of three Antarctic Survey Telescope (AST3-1), a 50/68 cm Schmidt-like equatorial-mount telescope, is the first trackable telescope of China operating in Antarctica and the biggest telescope located in Antarctic inland. AST3-1 obtained huge amounts of data in 2012 and we processed the time-series parts. Here we present light curves of 29 variable stars identified from ten-day observations in 2012 with AST3-1, including 22 newly discovered variable stars. 23 of them are eclipsing binaries and the others are pulsating stars. We present the properties of the 29 variable stars, including the classifications, periods and magnitude ranges in i band. For the 17 eclipsing binaries, the phased light curves are presented with the orbital period values well determined.

  1. The American Association of Variable Star Observers: Serving the Research Community in 2010 and Beyond

    Science.gov (United States)

    Templeton, Matthew R.; Henden, A. A.; Davis, K.; Kinne, R.; Watson, C.; Saladyga, M.; Waagen, E.; Beck, S.; Menali, G.; Price, A.; Turner, R.

    2010-05-01

    The American Association of Variable Star Observers (AAVSO) holds the largest single online database of variable star data in the world, collected from thousands of amateur and professional observers during the past century. One of our core missions is to preserve and distribute these data to the research community in service to the science of variable star astronomy. But as an organization, the AAVSO is much more than a data archive. Our services to the research community include: monitoring for and announcement of major astronomical events like novae and supernovae; organization and management of observing campaigns; support for satellite and other TOO observing programs by the professional community; creation of comparison star sequences and generation of charts for the observer community; and observational and other support for the amateur, professional, and educator communities in all things related to variable stars. As we begin a new century of variable star astronomy we invite you to take advantage of the services the AAVSO can provide, and to become a part of our organization yourselves. In this poster, we highlight some of the most important services the AAVSO can provide to the professional research community, as well as suggest ways in which your research may be enhanced with support from the AAVSO.

  2. A Photometric Variability Survey of Field K and M Dwarf Stars with HATNet

    CERN Document Server

    Hartman, J D; Noyes, R W; Sipöcz, B; Kovács, G; Mazeh, T; Shporer, A; Pál, A

    2009-01-01

    Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broad-band photometric variability of a sample of 27,560 field K and M dwarfs selected by color and proper-motion. A total of 3496 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1928 stars, including 79 eclipsing binaries, as secure variable star detections that are not high probability blends. We find that only 43 of these stars, including 7 of the eclipsing binaries, have previously been identified as variables or are blended with previously identified variables. One of the newly identified eclipsing binaries is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M_1 = M_2 = 0.258 +- 0.008 M_Sun and R_1 = R_2 = 0.289 +- 0.007 R_Sun. The radii of the component s...

  3. The EPOCH Project: I. Periodic Variable Stars in the EROS-2 LMC Database

    CERN Document Server

    Kim, Dae-Won; Bailer-Jones, Coryn A L; Byun, Yong-Ik; Chang, Seo-Won; Marquette, Jean-Baptiste; Shin, Min-Su

    2014-01-01

    The EPOCH (EROS-2 periodic variable star classification using machine learning) project aims to detect periodic variable stars in the EROS-2 light curve database. In this paper, we present the first result of the classification of periodic variable stars in the EROS-2 LMC database. In order to classify these variables, we first build a training set by compiling known variables in the Large Magellanic Could area from the OGLE and MACHO surveys. We crossmatch these variables with the EROS-2 sources and extract 22 variability features from 28,392 light curves of the corresponding EROS-2 sources. We then use Random Forests to classify the EROS-2 sources in the training set. We design the model to separate not only $\\delta$ Scuti stars, RR Lyraes, Cepheids, eclipsing binaries and long-period variables, the "superclasses", but also their subclasses, such as RRab, RRc, RRd and RRe for RR Lyraes, and similarly for the other variable types. The model trained using only the superclasses shows 99% recall and precision w...

  4. Luminous and Variable Stars in M31 and M33. II. Luminous Blue Variables, Candidate LBVs, Fe II Emission Line Stars, and Other Supergiants

    CERN Document Server

    Humphreys, Roberta M; Davidson, Kris; 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 Varaibles (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-SN stages of very massive stars. We have begun a survey of the evolved and un stable 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, quiesc...

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

    OpenAIRE

    López Coto, Rubén

    2015-01-01

    La historia de la astronomía es tan antigua como alcanzan nuestros registros. Todas las civilizaciones han estado interesadas en el estudio del cielo nocturno, sus objetos y fenómenos. Estas observaciones se realizaron a simple vista hasta el comienzo del siglo XVII, cuando Galileo Galilei empezó a usar un instrumento desarrollado recientemente llamado telescopio. Desde entonces, el rango de longitudes de onda accesible ha ido creciendo, con una explosión en el siglo XX gracias...

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

    OpenAIRE

    López Coto, Rubén; Fernández Sánchez, Enrique

    2015-01-01

    La historia de la astronomía es tan antigua como alcanzan nuestros registros. Todas las civilizaciones han estado interesadas en el estudio del cielo nocturno, sus objetos y fenómenos. Estas observaciones se realizaron a simple vista hasta el comienzo del siglo XVII, cuando Galileo Galilei empezó a usar un instrumento desarrollado recientemente llamado telescopio. Desde entonces, el rango de longitudes de onda accesible ha ido creciendo, con una explosión en el siglo XX gracias al desarrollo ...

  7. The OGLE Collection of Variable Stars. Over 45 000 RR Lyrae Stars in the Magellanic System

    CERN Document Server

    Soszyński, I; Szymański, M K; Wyrzykowski, Ł; Ulaczyk, K; Poleski, R; Pietrukowicz, P; Kozłowski, S; Skowron, D; Skowron, J; Mróz, P; Pawlak, M

    2016-01-01

    We present the largest collection of RR Lyrae stars in the Magellanic System and in its foreground. The sample consists of 45 451 RR Lyr stars, of which 39 082 were detected toward the Large Magellanic Cloud and 6369 toward the Small Magellanic Cloud. We provide long-term time-series photometric measurements collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV). We discuss several potential astrophysical applications of our collection: investigation of the structure of the Magellanic Clouds and the Galactic halo, studies of the globular clusters in the Magellanic System, analysis of double-mode RR Lyr stars, and searching for RR Lyr stars in eclipsing binary systems.

  8. Radial dependence of line profile variability in seven O9--B0.5 stars

    CERN Document Server

    Martins, F; Hillier, D J; Donati, J -F; Bouret, J -C

    2014-01-01

    Massive stars show a variety of spectral variability: presence of discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, radial velocity modulations. Our goal is to study the spectral variability of single OB stars to better understand the relation between photospheric and wind variability. For that, we rely on high spectral resolution, high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We investigate the variability of twelve spectral lines by means of the Temporal Variance Spectrum (TVS). The selected lines probe the radial structure of the atmosphere, from the photosphere to the outer wind. We also perform a spectroscopic analysis with atmosphere models to derive the stellar and wind properties, and to constrain the formation region of the selected lines. We show that variability is observed in the wind lines of all bright giants and supergiants, on a daily timescale. Lines form...

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

    Science.gov (United States)

    Larsen, K.

    2016-06-01

    (Abstract only) A century and one month ago (October 1915) Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, published An Introduction to the Study of Variable Stars. Issued in honor of the fiftieth anniversary of the founding of Vassar College, the work was meant to fill a void in the literature, namely as both an introduction to the topic of variable stars and as a manual explaining how they should be observed and the resulting data analyzed. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World's Fair in Chicago. The book covers the relevant history of and background on types of variable stars, star charts, catalogs, and the magnitude scale, then describes observing techniques, including visual, photographic, and photoelectric photometry. The work finishes with a discussion of light curves and patterns of variability, with a special emphasis on eclipsing binaries and long period variables. Furness's work is a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. This presentation will analyze both Furness's book and its reception in the scientific community, and draw parallels to current advice given to beginning variable star observers.

  10. Identification of Variable Stars in COROT's First Main Observing Field (LRc1)

    CERN Document Server

    Karoff, C; Erikson, A; Voss, H; Kabath, P; Wiese, T; Deleuil, M; Moutou, C; Meunier, J C; Deeg, H; 10.1086/519524

    2009-01-01

    The COROT space mission will monitor several target fields for up to 150 days to perform asteroseismology and to search for extrasolar planets by photometric transits. Variable stars in the target fields are important objects for additional scientific studies but can also disturb the search for planetary transits. A variability characterization of the target fields prior to COROT observations is therefore important for two reasons: to find interesting variable stars to monitor further and to make an analysis of the impact of the variable stars on detecting extrasolar planet transits with COROT. The Berlin Exoplanet Search Telescope (BEST) is a small wide-angle telescope dedicated to high-precision photometry. It has observed a 9 square degree field of view centered at (alpha, delta)=(19h00m00.0s, +00deg01'55.2") (J2000.0) over 98 nights to search for variable stars in the surroundings of the first long-run target field (LRc1) of the COROT space mission. In this data set we identified 92 periodic variable star...

  11. Automated classification of periodic variable stars detected by the wide-field infrared survey explorer

    Energy Technology Data Exchange (ETDEWEB)

    Masci, Frank J.; Grillmair, Carl J.; Cutri, Roc M. [Infrared Processing and Analysis Center, Caltech 100-22, Pasadena, CA 91125 (United States); Hoffman, Douglas I., E-mail: fmasci@ipac.caltech.edu [NASA Ames Research Center, Moffett Field, CA 94035 (United States)

    2014-07-01

    We describe a methodology to classify periodic variable stars identified using photometric time-series measurements constructed from the Wide-field Infrared Survey Explorer (WISE) full-mission single-exposure Source Databases. This will assist in the future construction of a WISE Variable Source Database that assigns variables to specific science classes as constrained by the WISE observing cadence with statistically meaningful classification probabilities. We have analyzed the WISE light curves of 8273 variable stars identified in previous optical variability surveys (MACHO, GCVS, and ASAS) and show that Fourier decomposition techniques can be extended into the mid-IR to assist with their classification. Combined with other periodic light-curve features, this sample is then used to train a machine-learned classifier based on the random forest (RF) method. Consistent with previous classification studies of variable stars in general, the RF machine-learned classifier is superior to other methods in terms of accuracy, robustness against outliers, and relative immunity to features that carry little or redundant class information. For the three most common classes identified by WISE: Algols, RR Lyrae, and W Ursae Majoris type variables, we obtain classification efficiencies of 80.7%, 82.7%, and 84.5% respectively using cross-validation analyses, with 95% confidence intervals of approximately ±2%. These accuracies are achieved at purity (or reliability) levels of 88.5%, 96.2%, and 87.8% respectively, similar to that achieved in previous automated classification studies of periodic variable stars.

  12. K2 Variable Catalogue II: Variable Stars and Eclipsing Binaries in K2 Fields 1 and 0

    CERN Document Server

    Armstrong, D J; Lam, K W F; McCormac, J; Walker, S R; Brown, D J A; Osborn, H P; Pollacco, D L; Spake, J

    2015-01-01

    We have created a catalogue of variable stars found from a search of the publicly available K2 mission data from Campaigns 1 and 0. This catalogue provides the identifiers of 8395 variable stars, including 199 candidate eclipsing binaries with periods up to 60d and 3871 periodic or quasi-periodic objects, with periods up to 20d for Field 1 and 15d for Field 0. Lightcurves are extracted and detrended from the available data. These are searched using a combination of algorithmic and human classification, leading to a classifier for each object as an eclipsing binary, sinusoidal periodic, quasi periodic, or aperiodic variable. The source of the variability is not identified, but could arise in the non-eclipsing binary cases from pulsation or stellar activity. Each object is cross-matched against variable star related guest observer proposals to the K2 mission, which specifies the variable type in some cases. The detrended lightcurves are also compared to lightcurves currently publicly available. The resulting ca...

  13. The Impact of the Astro2010 Recommendations on Variable Star Science

    CERN Document Server

    Walkowicz, Lucianne M; Anderson, Scott F; Bloom, Joshua S; Georgiev, Leonid; Grindlay, Josh; Long, Knox; Mukadam, Anjum; Prsa, Andrej; Pepper, Joshua; Rau, Arne; Sesar, Branimir; Silvestri, Nicole; Smith, Nathan; Stassun, Keivan; Szkody, Paula

    2009-01-01

    The next decade of survey astronomy has the potential to transform our knowledge of variable stars. Stellar variability underpins our knowledge of the cosmological distance ladder, and provides direct tests of stellar formation and evolution theory. Variable stars can also be used to probe the fundamental physics of gravity and degenerate material in ways that are otherwise impossible in the laboratory. The computational and engineering advances of the past decade have made large-scale, time-domain surveys an immediate reality. Some surveys proposed for the next decade promise to gather more data than in the prior cumulative history of astronomy. The actual implementation of these surveys will have broad implications for the types of science that will be enabled. We examine the design considerations for an optimal time-domain photometric survey dedicated to variable star science, including: observing cadence, wavelength coverage, photometric and astrometric accuracy, single-epoch and cumulative depth, overall...

  14. On Machine-Learned Classification of Variable Stars with Sparse and Noisy Time-Series Data

    CERN Document Server

    Richards, Joseph W; Butler, Nathaniel R; Bloom, Joshua S; Brewer, John M; Crellin-Quick, Arien; Higgins, Justin; Kennedy, Rachel; Rischard, Maxime

    2011-01-01

    With the coming data deluge from synoptic surveys, there is a growing need for frameworks that can quickly and automatically produce calibrated classification probabilities for newly-observed variables based on a small number of time-series measurements. In this paper, we introduce a methodology for variable-star classification, drawing from modern machine-learning techniques. We describe how to homogenize the information gleaned from light curves by selection and computation of real-numbered metrics ("feature"), detail methods to robustly estimate periodic light-curve features, introduce tree-ensemble methods for accurate variable star classification, and show how to rigorously evaluate the classification results using cross validation. On a 25-class data set of 1542 well-studied variable stars, we achieve a 22.8% overall classification error using the random forest classifier; this represents a 24% improvement over the best previous classifier on these data. This methodology is effective for identifying sam...

  15. Discovery of 13 New Variable Stars in the Field of the Open Cluster NGC 2168 (M35)

    Institute of Scientific and Technical Information of China (English)

    Juei-Hwa Hu; Wing-Huen Ip; Xiao-Bin Zhang; Zhao-Ji Jiang; Jun Ma; Xu Zhou

    2005-01-01

    A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems,one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δ Scuti stars.

  16. The variability of Sun-like stars: reproducing observed photometric trends

    CERN Document Server

    Shapiro, A I; Krivova, N A; Schmutz, W K; Ball, W T; Knaack, R; Rozanov, E V; Unruh, Y C

    2014-01-01

    The Sun and stars with low magnetic activity levels, become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behaviour and get fainter when their activity increases. We reproduce the observed photometric trends in stellar variations with a model that treats stars as hypothetical Suns with coverage by magnetic features different from that of the Sun. The presented model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and bright faculae. A stellar spectrum is calculated from spectra of the individual components, by weighting them with corresponding disc area coverages. The latter are obtained by extrapolating the solar dependences of spot and facular disc area coverages on chromospheric activity to stars with different levels of mean chromospheric activity. We have found that the contribution by starspots to the variability increases faster...

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

    CERN Document Server

    Skottfelt, Jesper; Jaimes, R Figuera; Jørgensen, U G; Kains, N; Ferro, A Arellano; Alsubai, K A; Bozza, V; Novati, S Calchi; Ciceri, S; DAgo, G; Dominik, M; Galianni, P; Gu, S -H; Harpsøe, K B W; Haugbølle, T; Hinse, T C; Hundertmark, M; Juncher, D; Korhonen, H; Liebig, C; Mancini, L; Popovas, A; Rabus, M; Rahvar, S; Scarpetta, G; Schmidt, R W; Snodgrass, C; Southworth, J; Starkey, D; Street, R A; Surdej, J; Wang, X -B; Wertz, O

    2014-01-01

    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 of NGC~6441, for which the variable star population of about 150 stars has been thoroughly examined by previous s...

  18. Variable X-Ray and UV emission from AGB stars: Accretion activity associated with binarity

    Science.gov (United States)

    Sahai, Raghvendra; Sanz-Forcada, Jorge; Sánchez Contreras, Carmen

    2016-07-01

    Almost all of our current understanding of the late evolutionary stages of (1 — 8) Mʘ stars is based on single-star models. However, binarity can drastically affect late stellar evolution, producing dramatic changes in the history and geometry of mass loss that occurs in stars as they evolve off the AGB to become planetary nebulae (PNe). A variety of binary models have been proposed, which can lead to the generation of accretion disks and magnetic fields, which in turn produce the highly collimated jets that have been proposed as the primary agents for the formation of bipolar and multipolar PNe. However, observational evidence of binarity in AGB stars is sorely lacking simply these stars are very luminous and variable, invalidating standard techniques for binary detection. Using an innovative technique of searching for UV emission from AGB stars with GALEX, we have identified a class of AGB stars with far- ultraviolet excesses (fuvAGB stars), that are likely candidates for active accretion associated with a binary companion. We have carried out a pilot survey for X-ray emission from fuvAGB stars. The X-ray fluxes are found to vary in a stochastic or quasi-periodic manner on roughly hour-long times-scales, and simultaneous UV observations show similar variations in the UV fluxes. We discuss several models for the X-ray emission and its variability and find that the most likely scenario for the origin of the X-ray (and FUV) emission involves accretion activity around a main-sequence companion star, with confinement by strong magnetic fields associated with the companion and/or an accretion disk around it.

  19. CURious Variables Experiment (CURVE). CCD Photometry and Variable Stars in the field of open cluster NGC 637

    CERN Document Server

    Pietrukowicz, P; Wisniewski, M; Kedzierski, P; Mularczyk, K; Zloczewski, K; Starczewski, S; Szaruga, K

    2006-01-01

    We present VI photometry for the open cluster NGC 637 which is located in the Cassiopeia region. Morphology of cluster color-magnitude diagram indicates that it is a young object with age of a few million years. The apparent distance modulus of the cluster is 13.9<(m-M)_V<14.3, while reddening is 0.69variable stars in NGC 637. One of the variables is a non-radial pulsating beta Cep-type star. Other one is a likely ellipsoidal variable, however its pulsating nature can not be excluded.

  20. On X-ray Variability in Active Binary Stars

    CERN Document Server

    Kashyap, V L; Kashyap, Vinay; Drake, Jeremy

    1999-01-01

    We compare the count-rates of active binaries observed by Einstein and ROSAT. We find significant evidence for short-term variability (approx 0.32) and marginal evidence for a larger variability at longer timescales (approx 0.38). Modeling this excess as cyclic variability, we place an upper limit on the relative amplitude of the cyclic component (I_cyc/I_min < 4) for active binaries, significantly less than the variations seen in the Solar X-ray output over the Solar cycle.

  1. Extreme Infrared Variables from UKIDSS - I. A Concentration in Star Forming Regions

    CERN Document Server

    Peña, C Contreras; Froebrich, D; Kumar, M S N; Goldstein, J; Drew, J E; Adamson, A; Davis, C J; Barentsen, G; Wright, N J

    2014-01-01

    We present initial results of the first panoramic search for high-amplitude near-infrared variability in the Galactic Plane. We analyse the widely separated two-epoch K-band photometry in the 5th and 7th data releases of the UKIDSS Galactic Plane Survey. We find 45 stars with \\Delta K > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is not yet included in the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions (SEDs) that support classification as Young Stellar Objects (YSOs). This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive pre...

  2. Magnetic field measurements and wind-line variability of OB-type stars

    CERN Document Server

    Schnerr, R S; Neiner, C; Verdugo, E; de Jong, J; Geers, V C; Wiersema, K; van Dalen, B; Tijani, A; Plaggenborg, B; Rygl, K L J

    2010-01-01

    Context. The first magnetic fields in O- and B-type stars that do not belong to the Bp-star class, have been discovered. The cyclic UV wind-line variability, which has been observed in a significant fraction of early-type stars, is likely to be related to such magnetic fields. Aims. We attempt to improve our understanding of massive-star magnetic fields, and observe twenty-five carefully-selected, OB-type stars. Methods. Of these stars we obtain 136 magnetic field strength measurements. We present the UV wind-line variability of all selected targets and summarise spectropolarimetric observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL, Pic du Midi, between December 1998 and November 2004. From the average Stokes I and V line profiles, derived using the LSD method, we measure the magnetic field strengths, radial velocities, and first moment of the line profiles. Results. No significant magnetic field is detected in any OB-type star that we observed. Typical 1{\\sigma} errors are betwee...

  3. An explanation for the curious mass loss history of massive stars from OB stars, through Luminous Blue Variables to Wolf-Rayet stars

    CERN Document Server

    Lamers, Henny J G L M

    2002-01-01

    The stellar winds of massive stars show large changes in mass-loss rates and terminal velocities during their evolution from O-star through the Luminous Blue Variable phase to the Wolf-Rayet phase. The luminosity remains approximately unchanged during these phases. These large changes in wind properties are explained in the context of the radiation driven wind theory, of which we consider four different models. They are due to the evolutionary changes in radius, gravity and surface composition and to the change from optically thin (in continuum) line driven winds to optically thick radiation driven winds.

  4. Analysis of the variability in the sdB star KIC 10670103: DFA approach

    Science.gov (United States)

    Zebende, Gilney F.; Fernandez, Basilio F.; Pereira, Marildo G.

    2017-01-01

    The brightness variation of the stars is an object of study in astronomy and astrophysics for representing the rich inherent source of physical information. Launched in 2009, the Kepler spacecraft with the primary mission of identifying equivalent to the Earth by the Sun transits also gave birth to thousands of light curves of targets of scientific interest. KIC 10670103, the richest pulsating sub-dwarf B (sdB) star, is one of the many stars identified by the mission. With 3.72 yr of Kepler spacecraft observations, we analysed in this paper the light curve of this sdB star, by the detrended fluctuation analysis (DFA) method. The behaviour of this pulsating star reveals self-affinity at specific time-scales, with changes in DFA exponent, αDFA. This fact suggests some light variability in KIC 10670103, as for example, from a non-periodic to a periodic case, among others. Therefore, we propose to connect the pulsation pattern of the KIC 10670103 star, which presents trends and non-stationarity, with the αDFA exponent. In this sense, we obtain five values of αDFA related to the light variability properties of KIC 10670103. A pictorial figure will describe the relationship between these variables.

  5. A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

    CERN Document Server

    Bernhard, K; Otero, S; Paunzen, E

    2015-01-01

    The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as alpha2 Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. In total, we found 323...

  6. Multiperiodicity, modulations and flip-flops in variable star light curves I. Carrier fit method

    CERN Document Server

    Pelt, J; Mantere, M J; Tuominen, I

    2011-01-01

    The light curves of variable stars are commonly described using simple trigonometric models, that make use of the assumption that the model parameters are constant in time. This assumption, however, is often violated, and consequently, time series models with components that vary slowly in time are of great interest. In this paper we introduce a class of data analysis and visualization methods which can be applied in many different contexts of variable star research, for example spotted stars, variables showing the Blazhko effect, and the spin-down of rapid rotators. The methods proposed are of explorative type, and can be of significant aid when performing a more thorough data analysis and interpretation with a more conventional method.Our methods are based on a straightforward decomposition of the input time series into a fast "clocking" periodicity and smooth modulating curves. The fast frequency, referred to as the carrier frequency, can be obtained from earlier observations (for instance in the case of p...

  7. The nature of the light variability of magnetic Of?p star HD 191612

    CERN Document Server

    Krticka, J

    2016-01-01

    A small fraction of hot OBA stars host global magnetic fields with field strengths of the order of 0.1-10 kG. This leads to the creation of persistent surface structures (spots) in stars with sufficiently weak winds as a result of the radiative diffusion. These spots become evident in spectroscopic and photometric variability. This type of variability is not expected in stars with strong winds, where the wind inhibits the radiative diffusion. Therefore, a weak photometric variability of the magnetic Of?p star HD 191612 is attributed to the light absorption in the circumstellar clouds. We study the nature of the photometric variability of HD 191612. We assume that the variability results from variable wind blanketing induced by surface variations of the magnetic field tilt and modulated by stellar rotation. We used our global kinetic equilibrium (NLTE) wind models with radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the stellar emergent flux. Our models de...

  8. Electronic version of the third volume of the general catalogue of variable stars with improved coordinates

    Science.gov (United States)

    Samus', N. N.; Durlevich, O. V.; Zharova, A. V.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Williams, D. B.; Hazen, M. L.

    2006-04-01

    We present a new electronic version of the third volume of the fourth edition of the General Catalogue of Variable Stars (GCVS) that contains data on 13 855 variables in the constellations Pavo-Vulpecula. The Name Lists of Variable Stars from no. 67 to no. 77 were included in the new version. The main distinctive feature of the new version is that improved J2000.0 equatorial coordinates (including those for 6163 stars corrected for the proper motions) based on the identifications with positional catalogues using finding charts and on our new measurements are presented for 13 812 stars. We searched for a number of stars on original plates from the plate stacks of several observatories and using images from digital sky surveys. Apart from the complete update of the positional information, we made several corrections that were found to be necessary after the publication of the GCVS Volume III (1985) and several corrections of the information about the variability features based on photometry from currently available automatic sky surveys. A number of problem identifications are described in detail. The new version completes our long-term work on the complete revision of the positional information in the GCVS. In the Conclusions, we give a list of references to new Internet resources.

  9. A photometric variability study of massive stars in Cygnus OB2

    CERN Document Server

    Salas, J; Barbá, R H

    2014-01-01

    We have conducted a 1.5 year-long variability study of the stars in the Cygnus OB2 association, the region in the northern hemisphere with the highest density of optically visible massive stars. The survey was conducted using four pointings in the Johnson $R$ and $I$ bands with a 35 cm Meade LX200-ACF telescope equipped with a 3.2 Mpixel SBIG ST10-XME CCD camera and includes 300+ epochs in each filter. A total of 1425 objects were observed with limiting magnitudes of 15 in $R$ and 14 in $I$. The photometry was calibrated using reference stars with existing $UBVJHK$ photometry. Bright stars have precisions better than 0.01 magnitudes, allowing us to detect 52 confirmed and 19 candidate variables, many of them massive stars without previous detections as variables. Variables are classified as eclipsing, pulsating, irregular/long period, and Be. We derive the phased light curves for the eclipsing binaries, with periods ranging from 1.3 to 8.5 days.

  10. A search for new variable stars using digitized Moscow collection plates

    CERN Document Server

    Sokolovsky, Kirill; Kolesnikova, Daria; Lebedev, Alexandr; Samus, Nikolai; Sat, Lyudmila; Zubareva, Alexandra

    2014-01-01

    By digitizing astronomical photographic plates one may extract full information stored on them, something that could not be practically achieved with classical analogue methods. We are developing algorithms for variable objects search using digitized photographic images and apply them to 30cm (10x10 deg. field of view) plates obtained with the 40cm astrograph in 1940-90s and digitized with a flatbed scanner. Having more than 100 such plates per field, we conduct a census of high-amplitude (>0.3m) variable stars changing their brightness in the range 13variable stars. We estimate that 1.2 +/- 0.1% of all stars show easily-detectable light variations; 0.7 +/- 0.1% of the stars are eclipsing binaries (64 +/- 4% of them are EA type, 22 +/- 2% are EW type and 14 +/- 2% are EB type); 0.3 +/- 0.1% of the stars are red variable giants and supergiants of M, SR and L types.

  11. Galactic membership of BL Her type variable stars

    CERN Document Server

    Jurkovic, Monika I; Ninković, Slobodan

    2016-01-01

    As the RR Lyrae stars evolve on the Hertzsprung-Russell diagram they are believed to become short period Type II Cepheids, known as BL Her type (with a pulsation period from $1$ to $3-8$ days). Assuming that their mass is around $0.5 - 0.6 {\\rm M}_{\\odot}$, and that they are low metallicity objects, they were thought to belong to the halo of the Milky Way. We investigated seven Galactic short period Type II Cepheids (BL Her, SW Tau, V553 Cen, DQ And, BD Cas, V383 Cyg, and KT Com) in order to establish their membership within the Galactic structure using the kinematic approach. $Gaia$ should provide us with more data needed to conduct the study of the whole sample.

  12. Galactic membership of BL Her type variable stars

    Science.gov (United States)

    Jurkovic, M. I.; Stojanovic, M.; Ninkovic, S.

    2016-05-01

    As the RR Lyrae stars evolve on the Hertzsprung-Russell diagram they are believed to become short period Type II Cepheids, known as BL Her type (with a pulsation period from 1 to 3-8 days). Assuming that their mass is around 0.5-0.6M_Sol, and that they are low metallicity objects, they were thought to belong to the halo of the Milky Way. We investigated seven Galactic short period Type II Cepheids (BL Her, SW Tau, V553 Cen, DQ And, BD Cas, V383 Cyg, and KT Com) in order to establish their membership within the Galactic structure using the kinematic approach. Gaia should provide us with more data needed to conduct the study of the whole sample.

  13. Automatic Classification of Variable Stars in Catalogs with missing data

    CERN Document Server

    Pichara, Karim

    2013-01-01

    We present an automatic classification method for astronomical catalogs with missing data. We use Bayesian networks, a probabilistic graphical model, that allows us to perform inference to pre- dict missing values given observed data and dependency relationships between variables. To learn a Bayesian network from incomplete data, we use an iterative algorithm that utilises 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, 2MASS 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 few percent and by 15% for quasar detection while keeping the computational co...

  14. Variable Evolved Stars and YSOs Discovered in the Large Magellanic Cloud using the SAGE Survey

    CERN Document Server

    Vijh, Uma P; Babler, B; Block, M; Bracker, S; Engelbracht, C W; For, B; Gordon, K; Hora, J; Indebetouw, R; Leitherer, C; Meade, M; Misselt, K; Sewilo, M; Srinivasan, S; Whitney, B

    2008-01-01

    We present initial results and source lists of variable sources in the Large Magellanic Cloud (LMC) for which we detect thermal infrared variability from the SAGE (Surveying the Agents of a Galaxy's Evolution) survey, which had 2 epochs of photometry separated by three months. The SAGE survey mapped a 7 degree by 7 degree region of the LMC using the IRAC and the MIPS instruments on board Spitzer. Variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8, 8.0 \\micron bands and the MIPS 24 \\micron bands. An error-weighted flux difference between the two epochs is used to assess the variability. Of the ~ 3 million sources detected at both epochs we find ~ 2,000 variable sources for which we provide electronic catalogs. Most of the variable sources can be classified as asymptotic giant branch (AGB) stars. A large fraction (> 66%) of the extreme AGB stars are variable and only smaller fractions of carbon-rich (6.1%) and oxygen-rich (2.0%) stars are detected as variable. We also detect a populat...

  15. Chromospherically active stars. II - HD 82558, a young single BY Draconis variable

    Science.gov (United States)

    Fekel, Francis C.; Bopp, Bernard W.; Africano, John L.; Goodrich, Bret D.; Palmer, Leigh Hunter

    1986-01-01

    It is presently noted that the HD 82558 chromospherically active star is a young and rapidly rotating K2 V single BY Draconis variable with very strong far-UV emission features and an H-alpha line filled to the continuum level by emission. HD 82558 has constant velocity and is not a member of the Hyades Supercluster. Its light curve behavior, which appears to have been stable for several hundred rotation cycles, is reminiscent of that of the young, rapidly rotating, single K V variable H II 1883 in the Pleiades; this stability may be characteristic of young, single, chromospherically active stars.

  16. Pre-main sequence variable stars in young open cluster NGC 1893

    OpenAIRE

    Lata, Sneh; Pandey, A.K.(Indian Institute of Technology Bombay (IIT), Mumbai, India); Chen, W. P.; Maheswar, G.; Chauhan, Neelam

    2012-01-01

    We present results of multi-epoch (fourteen nights during 2007-2010) $V$-band photometry of the cluster NGC 1893 region to identify photometric variable stars in the cluster. The study identified a total of 53 stars showing photometric variability. The members associated with the region are identified on the basis of spectral energy distribution, $J-H/H-K$ two colour diagram and $V/V-I$ colour-magnitude diagram. The ages and masses of the majority of pre-main-sequence sources are found to be ...

  17. 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.

  18. Variability in young very low mass stars: two surprises from spectrophotometric monitoring

    Science.gov (United States)

    Bozhinova, I.; Scholz, A.; Eislöffel, J.

    2016-05-01

    We present simultaneous photometric and spectroscopic observations of seven young and highly variable M dwarfs in star-forming regions in Orion, conducted in four observing nights with FOcal Reducer and low dispersion Spectrograph2 at European Southern Observatory/VLT. All seven targets show significant photometric variability in the I band, with amplitudes between 0.1-0.8 mag, The spectra, however, remain remarkably constant, with spectral type changes less than 0.5 subtypes. Thus, the brightness changes are not caused by veiling that `fills in' absorption features. Three objects in the σ Ori cluster (age ˜3 Myr) exhibit strong Hα emission and Hα variability, in addition to the continuum variations. Their behaviour is mostly consistent with the presence of spots with temperature of ˜300 K above the photosphere and filling factors between 0.2-0.4, in contrast to typical hotspots observed in more massive stars. The remaining targets near ɛ Ori, likely to be older, show eclipse-like light curves, no significant Hα activity and are better represented by variable extinction due to circumstellar material. Interestingly, two of them show no evidence of infrared excess emission. Our study shows that high-amplitude variability in young very low mass stars can be caused by different phenomena than in more massive T Tauri stars and can persist when the disc has disappeared and accretion has ceased.

  19. The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda II

    CERN Document Server

    Pritzl, B J; Jacoby, G H; Costa, G S D; Pritzl, Barton J.; Armandroff, Taft E.; Jacoby, George H.

    2004-01-01

    (abridged) We present the results of a variable star search in Andromeda II, a dwarf spheroidal galaxy companion to M31, using HST/WFPC2 observations. Seventy-three variables were found, one of which is an anomalous Cepheid while the others are RR Lyrae stars. The anomalous Cepheid has properties consistent with those found in other dwarf spheroidal galaxies. For the RR Lyrae stars, the mean periods are 0.571 day and 0.363 day for the fundamental mode and first-overtone mode stars, respectively. With this fundamental mode mean period and the mean metallicity determined from the red giant branch (=-1.49), Andromeda II follows the period-metallicity relation defined by the Galactic globular clusters and other dwarf spheroidal galaxies. We also find that the properties of the RR Lyrae stars themselves indicate a mean abundance that is consistent with that determined from the red giants. There is, however, a significant spread among the RR Lyrae stars in the period-amplitude diagram, which is possibly related to ...

  20. The Nainital-Cape Survey-III : A Search for Pulsational Variability in Chemically Peculiar Stars

    CERN Document Server

    Joshi, S; Chakradhari, N K; Tiwari, S K; Billaud, C

    2009-01-01

    The Nainital-Cape survey is a dedicated research programme to search and study pulsational variability in chemically peculiar stars in the Northern Hemisphere. The aim of the survey is to search such chemically peculiar stars which are pulsationally unstable. The observations of the sample stars were carried out in high-speed photometric mode using a three-channel fast photometer attached to the 1.04-m Sampurnanand telescope at ARIES. The new photometric observations confirmed that the pulsational period of star HD25515 is 2.78-hrs. The repeated time-series observations of HD113878 and HD118660 revealed that previously known frequencies are indeed present in the new data sets. We have estimated the distances, absolute magnitudes, effective temperatures and luminosities of these stars. Their positions in the H-R diagram indicate that HD25515 and HD118660 lie near the main-sequence while HD113878 is an evolved star. We also present a catalogue of 61 stars classified as null results, along with the corresponding...

  1. A Quest for PMS candidate stars at low metallicity: Variable HAe/Be and Be stars in the Small Magellanic Cloud

    CERN Document Server

    De Wit, W J; Lamers, Henny J G L M; Lesquoy, E; Marquette, J B

    2003-01-01

    We report the discovery of 5 new Herbig Ae/Be candidate stars in the Small Magellanic Cloud in addition to the 2 reported in Beaulieu et al. (2001). We discuss these 7 HAeBe candidate stars in terms of (1) their irregular photometric variability, (2) their near infrared emission, (3) their Halpha emission and (4) their spectral type. One star has the typical photometric behaviour that is observed only among Pre-Main Sequence UX Orionis type stars. The objects are more luminous than Galactic HAeBe stars and Large Magellanic Cloud HAeBe candidates of the same spectral type. The stars were discovered in a systematic search for variable stars in a subset of the EROS2 database consisting of 115,612 stars in a field of 24x24 arcmin in the Small Magellanic Cloud. In total we discovered 504 variable stars. After classifying the different objects according to their type of variability, we concentrate on 7 blue objects with irregular photometric behaviour. We cross-identified these objects with emission line catalogues...

  2. Deep near-IR variability survey of pre-main-sequence stars in Rho Ophiuchi

    CERN Document Server

    de Oliveira, Catarina Alves

    2008-01-01

    Variability is a common characteristic of pre-main-sequence stars (PMS). Near-IR variability surveys of young stellar objects (YSOs) can probe stellar and circumstellar environments and provide information about the dynamics of the on going magnetic and accretion processes. Furthermore, variability can be used as a tool to uncover new cluster members in star formation regions. We hope to achieve the deepest near-IR variability study of YSOs targeting the Rho Ophiuchi cluster. Fourteen epochs of observations were obtained with the Wide Field Camera (WFCAM) at the UKIRT telescope scheduled in a manner that allowed the study of variability on timescales of days, months, and years. Statistical tools, such as the multi-band cross correlation index and the reduced chi-square, were used to disentangle signals of variability from noise. Variability characteristics are compared to existing models of YSOs in order to relate them to physical processes, and then used to select new candidate members of this star-forming r...

  3. Precise High-Cadence Time Series of Five Variable Young Stars in Auriga with MOST

    CERN Document Server

    Cody, Ann Marie; Hillenbrand, Lynne A; Matthews, Jaymie M; Kallinger, Thomas

    2013-01-01

    To explore young star variability on a large range of timescales, we have used the MOST satellite to obtain 24 days of continuous, sub-minute cadence, high-precision optical photometry on a field of classical and weak-lined T Tauri stars (TTS) in the Taurus-Auriga star formation complex. Observations of AB Aurigae, SU Aurigae, V396 Aurigae, V397 Aurigae, and HD 31305 reveal brightness fluctuations at the 1-10% level on timescales of hours to weeks. We have further assessed the variability properties with Fourier, wavelet, and autocorrelation techniques, identifying one significant period per star. We present spot models in an attempt to fit the periodicities, but find that we cannot fully account for the observed variability. Rather, all stars exhibit a mixture of periodic and aperiodic behavior, with the latter dominating stochastically on timescales less than several days. After removal of the main periodicity, periodograms for each light curve display power law trends consistent with those seen for other y...

  4. First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group

    Science.gov (United States)

    2003-05-01

    First-Ever Census of Variable Mira-Type Stars in Galaxy Outsidethe Local Group Summary An international team led by ESO astronomer Marina Rejkuba [1] has discovered more than 1000 luminous red variable stars in the nearby elliptical galaxy Centaurus A (NGC 5128) . Brightness changes and periods of these stars were measured accurately and reveal that they are mostly cool long-period variable stars of the so-called "Mira-type" . The observed variability is caused by stellar pulsation. This is the first time a detailed census of variable stars has been accomplished for a galaxy outside the Local Group of Galaxies (of which the Milky Way galaxy in which we live is a member). It also opens an entirely new window towards the detailed study of stellar content and evolution of giant elliptical galaxies . These massive objects are presumed to play a major role in the gravitational assembly of galaxy clusters in the Universe (especially during the early phases). This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory . PR Photo 14a/03 : Colour image of the peculiar galaxy Centaurus A . PR Photo 14b/03 : Location of the fields in Centaurus A, now studied. PR Photo 14c/03 : "Field 1" in Centaurus A (visual light; FORS1). PR Photo 14d/03 : "Field 2" in Centaurus A (visual light; FORS1). PR Photo 14e/03 : "Field 1" in Centaurus A (near-infrared; ISAAC). PR Photo 14f/03 : "Field 2" in Centaurus A (near-infrared; ISAAC). PR Photo 14g/03 : Light variation of six variable stars in Centaurus A PR Photo 14h/03 : Light variation of stars in Centaurus A (Animated GIF) PR Photo 14i/03 : Light curves of four variable stars in Centaurus A. Mira-type variable stars Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred (0.3%) displays brightness variations and is referred to by astronomers as a

  5. Variable Stars in the Fornax dSph Galaxy. III. The Globular Cluster Fornax 5

    CERN Document Server

    Greco, Claudia; Catelan, Marcio; Held, Enrico V; Poretti, Ennio; Gullieuszik, Marco; Maio, Marcella; Rest, Armin; De Lee, Nathan; Smith, Horace A; Pritzl, Barton J

    2009-01-01

    We present a new study of the variable star population in globular cluster 5 of the Fornax dwarf spheroidal galaxy, based on B and V time series photometry obtained with the MagIC camera of the 6.5 m Magellan Clay telescope and complementary HST archive data. Light curves and accurate periodicities were obtained for 30 RR Lyrae stars and 1 SX Phoenicis variable. The RR Lyrae sample includes 15 fundamental-mode pulsators, 13 first-overtone pulsators, 1 candidate double-mode pulsator and one RR Lyrae star with uncertain type classification. The average and minimum periods of the ab-type RR Lyrae stars, =0.590 days, P(ab,min)=0.53297 days, and the position in the horizontal branch type--metallicity plane, indicate that the cluster has Oosterhoff-intermediate properties, basically confirming previous indications by Mackey & Gilmore (2003b), although with some differences both in the period and type classification of individual variables. The average apparent magnitude of the Fornax 5 RR Lyrae stars is =21.35 ...

  6. Research study of Beta Cephei variable stars using data from OAO-2

    Science.gov (United States)

    Lesh, J. R.

    1975-01-01

    Photometric data from the Wisconsin Experiment package on OAO-2 were obtained for six Beta Cephei variable stars. The data were reduced in accordance with the OAO 2/Wisconsin Experiment Package Photometer Users Guide. For delta Cet and gamma Peg, there were enough data points to form reliable composite light curves at seven or eight ultraviolet wavelengths. The light curves are well represented by sine waves in phase with the blue light curve for each star. The amplitude of the light variation increases with shorter wavelengths. For theta Oph, epsilon Cen, eta Sco, and Lambda Sco, mean magnitudes and light ranges were obtained at several ultraviolet wavelengths. No significant differences were found between the mean, de-reddened ultraviolet colors of the observed stars, and the mean values for standard stars computed by Bottemiller. An attempt to derive a temperature scale from a comparison of the observed ultraviolet colors with Kurucz models was unsuccessful.

  7. Fibonacci Sequences and the Multiperiodicity of the Variable Star UW Herculis

    Institute of Scientific and Technical Information of China (English)

    Juan Garc(i)a Escudero

    2003-01-01

    We present an application of the methods recently developed for thestudy of quasicrystal structures to the analysis of multiperiodicity of semiregularvariables. A light curve analysis of UW Her shows frequencies that can be in-cluded within the general scheme characterizing the Fourier spectra of Fibonacciquasiperiodic sequences. The analysed data come from the BAA Variable Star Sec-tion computerised archive.

  8. Variable central stars of young planetary nebulae. I. Photometric multisite observations of IC 418.

    Science.gov (United States)

    Handler, G.; Mendez, R. H.; Medupe, R.; Costero, R.; Birch, P. V.; Alvarez, M.; Sullivan, D. J.; Kurtz, D. W.; Herrero, A.; Guerrero, M. A.; Ciardullo, R.; Breger, M.

    1997-04-01

    We report the results of a photometric multisite campaign devoted to HD 35914, the variable central star of the Planetary Nebula IC 418. From the analysis of 120 hours of data acquired with a variety of techniques, we find that HD 35914 exhibits two distinct kinds of variability: irregular light modulation with a time scale of days, as well as cyclic variations with a time scale of 6.5 hours. The short-term variations are not strictly periodic, and cannot be reasonably explained by multiperiodicity; they appear to be semiregular. The star is generally redder when it is brighter; this behavior appears to be connected with the long-term variability. A re-analysis of most of the older data obtained for HD 35914 by various researchers suggests that the basic behavior of the star did not change during the last 15 years. We carefully discuss all the possible causes for the light variations of the star. Rotational modulation of surface features cannot explain the observations, and binarity is unlikely. Pulsations may be excited, but wind variability (or a combination of both) can also not be ruled out.

  9. Variable Stars in the LMC Globular Cluster NGC 2257 New: Results Based on 2007-08 B, V Photometry

    Science.gov (United States)

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

    2009-09-01

    The variable star population in the Large Magellanic Cloud outer-halo globular cluster NGC 2257 has been reinvestigated using photometry (to ~20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9-m telescope on 14 nights in Dec'07 and Jan'08. The derived periods of most of the stars are consistent with the pulsation periods derived previously, and where there were discrepancies these have been resolved. Accurate Fourier coefficients and parameters were computed for the B and V light curves. Six new variable stars were discovered (V45-V50), including a bright candidate long-period variable star showing secondary oscillations (V45). Examination of archival HST images and previously-published photometry shows that the excess brightness of two bright RR Lyrae stars (V48, V50) is due to contamination from close red giant branch stars. Among the previously known variable stars three double-mode (RRd) RR Lyrae stars (V8, V16 and V34) and several Blazhko variables were discovered. The total number of cluster variable stars now stands at forty-seven: 23 RRab stars, four of which show Blazhko light-curve variations; 20 RRc stars, one showing clear Blazhko variations and another showing possible Blazhko variations; the three RRd stars, all having the dominant period ~0.36 day and period ratios P1/P0~0.7450, and the LPV located near the tip of the red giant branch. A comparison with similar stars in other environments shows that the RRd stars in NGC 2257 are most similar to those in IC 4499.

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

    CERN Document Server

    Ng, Y K

    1996-01-01

    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 those found by Azzopardi et al. (1991). Serendipity provides the suggestion, that their carbon stars might not be located inside, but behind the bulge in the Sagittarius dwarf galaxy.

  11. Hands-On Astrophysics: Variable Stars in Math, Science, and Computer Education

    Science.gov (United States)

    Mattei, J. A.; Percy, J. R.

    1999-12-01

    Hands-On Astrophysics (HOA): Variable Stars in Math, Science, and Computer Education, is a project recently developed by the American Association of Variable Star Observers (AAVSO) with funds from the National Science Foundation. HOA uses the unique methods and the international database of the AAVSO to develop and integrate students' math and science skills through variable star observation and analysis. It can provide an understanding of basic astronomy concepts, as well as interdisciplinary connections. Most of all, it motivates the user by exposing them to the excitement of doing real science with real data. Project materials include: a database of 600,000 variable star observations; VSTAR (a data plotting and analysis program), and other user friendly software; 31 slides and 14 prints of five constellations; 45 variable star finder charts; an instructional videotape in three 15-minute segments; and a 560-page student's and teacher's manual. These materials support the National Standards for Science and Math education by directly involving the students in the scientific process. Hands-On Astrophysics is designed to be flexible. It is organized so that it can be used at many levels, in many contexts: for classroom use from high school to college level, or for individual projects. In addition, communication and support can be found through the AAVSO home page on the World Wide Web: http://www.aavso.org. The HOA materials can be ordered through this web site or from the AAVSO, 25 Birch Street Cambridge, MA 02138, USA. We gratefully acknowledge the education grant ESI-9154091 from the National Science Foundation which funded the development of this project.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-03-01

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

  13. Variable stars in the newly discovered Milky Way satellite in Bootes

    CERN Document Server

    Dall'Ora, M; Kinemuchi, K; Ripepi, V; Marconi, M; Fabrizio, L D; Greco, C; Rodgers, C T; Kuehn, C; Smith, H A

    2006-01-01

    We present $V,I$ light curves for 12 variable stars identified in the newly discovered satellite of the Milky Way in the Bootes constellation (Belokurov et al. 2006).Our sample includes 11 RR Lyrae stars (5 first overtone, 5 fundamental mode and 1 double mode pulsator),and one long period variable close to the galaxy red giant branch tip. The RR Lyrae stars trace very well the average $V$ luminosity of the galaxy horizontal branch, leading to a true distance modulus for the galaxy of $\\mu_0$=19.11 $\\pm$ 0.08 mag for an assumed metal abundance of [Fe/H]=-2.5 (Monoz et al. 2006), and for $E(B-V)$=0.02 mag. Average periods are =0.69 d and =0.37 d for {\\it ab-} and {\\it c-} type RR Lyrae stars, respectively, making of Bootes the second pure Oosterhoff type II (OoII) dSph after Ursa Minor. The location of the double mode RR Lyrae (RRd) in the Petersen diagram is consistent with RRd stars in OoII clusters, and corresponds to an intrinsic luminosity of $log L/logL\\odot$=1.72 (for Z=10$^{-4}$ and M=0.80 M$\\odot$) acc...

  14. Variable stars in the ultra-faint dwarf spheroidal galaxy Ursa Major I

    CERN Document Server

    Garofalo, Alessia; Clementini, Gisella; Ripepi, Vincenzo; Dall'Ora, Massimo; Moretti, Maria Ida; Coppola, Giuseppina; Musella, Ilaria; Marconi, Marcella

    2013-01-01

    We have performed the first study of the variable star population of Ursa Major I (UMa I), an ultra-faint dwarf satellite recently discovered around the Milky Way by the Sloan Digital Sky Survey. Combining time series observations in the B and V bands from four different telescopes, we have identified seven RR Lyrae stars in UMa I, of which five are fundamental-mode (RRab) and two are first-overtone pulsators (RRc). Our V, B-V color-magnitude diagram of UMa I reaches V~23 mag (at a signal-to-noise ratio of ~ 6) and shows features typical of a single old stellar population. The mean pulsation period of the RRab stars = 0.628, {\\sigma} = 0.071 days (or = 0.599, {\\sigma} = 0.032 days, if V4, the longest period and brightest variable, is discarded) and the position on the period-amplitude diagram suggest an Oosterhoff-intermediate classification for the galaxy. The RR Lyrae stars trace the galaxy horizontal branch at an average apparent magnitude of = 20.43 +/- 0.02 mag (average on 6 stars and discarding V4), ...

  15. The ancient stellar population of M32: RR Lyr Variable stars confirmed

    CERN Document Server

    Fiorentino, G; Tolstoy, E; Clementini, G; Saha, A

    2012-01-01

    Using archival multi--epoch ACS/WFC images in the F606W and F814W filters of a resolved stellar field in Local Group dwarf elliptical galaxy M32 we have made an accurate Colour-Magnitude Diagram and a careful search for RR Lyr variable stars. We identified 416 bona fide RR Lyr stars over our field of view, and their spatial distribution shows a rising number density towards the centre of M32. These new observations clearly confirm the tentative result of Fiorentino et al. (2010), on a much smaller field of view, associating an ancient population of RR Lyr variables to M32. We associate at least 83 RR Lyr stars in our field to M32. In addition the detection of 4 Anomalous Cepheids with masses in the range 1.2-1.9 Mo indicates the presence of relatively young, 1-4 Gyr old, stars in this field. They are most likely associated to the presence of the blue plume in the Colour-Magnitude Diagram. However these young stars are unlikely to be associated with M32 because the radial distribution of the blue plume does no...

  16. Lattice Structure in Astrophysics: A reconsideration of White Dwarfs, Variables, and Wolf-Rayet Stars

    Science.gov (United States)

    Robitaille, Pierre-Marie

    2016-03-01

    Stars of the main sequence display a mass-luminosity relation which indicates that they share a common building block (hydrogen) and lattice structure (hexagonal planar) with the solar photosphere. White dwarfs however display very low luminosity in spite of their elevated color temperature. Rather than postulate that these stars represent degenerate matter, as Eddington and Chandrasekhar were forced to assume given their gaseous models, within the context of a Liquid Metallic Hydrogen Solar Model white dwarfs might simply be thought as possessing a different lattice structure (e.g. body centered cubic) and hence a lowered emissivity. They do not need to possess exceeding densities, reduced radii, and degeneracy in order to account for their lowered emissivity. Similarly, variable stars might well be oscillating between lattices types wherein the energy differences involved in the transformations are small. Other stars, such as Wolf-Rayet stars, which lack photospheric emission, might be too hot to enable a discrete lattice to form. Though condensed, the photosphere in that case would have a lattice which is so poorly organized that its emissivity is trivial. Nonetheless, the broad emission lines of Wolf-Rayet stars indicates that these objects are not breaking apart but rather, are important sites of condensation.

  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. Periodic variable stars in CoRoT field LRa02 observed with BEST II

    CERN Document Server

    Kabath, P; Rauer, H; Pasternacki, T; Csizmadia, Sz; Chini, R; Lemke, R; Murphy, M; Fruth, T; Titz, R; Eigmueller, P

    2009-01-01

    The Berlin Exoplanet Search Telescope II (BEST II) is a small wide field-of-view photometric survey telescope system located at the Observatorio Cerro Armazones, Chile. The high duty cycle combined with excellent observing conditions and millimagnitude photometric precision makes this instrument suitable for ground based support observations for the CoRoT space mission. Photometric data of the CoRoT LRa02 target field collected between November 2008 and March 2009 were analysed for stellar variability. The presented results will help in the future analysis of the CoRoT data, particularly in additional science programs related to variable stars. BEST II observes selected CoRoT target fields ahead of the space mission. The photometric data acquired are searched for stellar variability, periodic variable stars are identified with time series analysis of the obtained stellar light curves. We obtained the light curves of 104335 stars in the CoRoT LRa02 field over 41 nights. Variability was detected in light curves...

  19. Variable stars in the VVV globular clusters. I. 2MASS-GC02 and Terzan10

    CERN Document Server

    Alonso-García, Javier; Catelan, Márcio; Ramos, Rodrigo Contreras; Gran, Felipe; Amigo, Pía; Leyton, Paul; Minniti, Dante

    2014-01-01

    The VISTA Variables in the Via Lactea (VVV) ESO Public Survey is opening a new window to study the inner Galactic globular clusters using their variable stars. These globular clusters have been neglected in the past due to the difficulties caused by the presence of an elevated extinction and high field stellar densities in their lines of sight. However, the discovery and study of any present variables in these clusters, especially RRLyrae stars, can help to greatly improve the accuracy of their physical parameters. It can also help to shed some light on the interrogations brought by the intriguing Oosterhoff dichotomy in the Galactic globular cluster system. In a series of papers we plan to explore the variable stars in the globular clusters falling inside the field of the VVV survey. In this first paper we search and study the variables present in two highly-reddened, moderately metal-poor, faint, inner Galactic globular clusters: 2MASS-GC02 and Terzan10. We report the discovery of sizable populations of RR ...

  20. Optical and near-infrared spectrophotometric properties of Long Period Variables and other luminous red stars

    CERN Document Server

    Alvarez, R; Plez, B; Wood, P R

    2000-01-01

    Based on a new and large sample of optical and near-infrared spectra obtained at the Mount Stromlo and Siding Spring Observatories (Lancon & Wood 1998; Lancon & Wood, in preparation), spectrophotometric properties of cool oxygen- and carbon-rich Long Period Variables and supergiants are presented. Temperatures of oxygen-rich stars are assigned by comparison with synthetic spectra computed from up-to-date oxygen-rich model atmosphere grids. The existence of reliable optical and near-infrared temperature indicators is investigated. A narrow relation between the bolometric correction BC(I) and the broad-band colour I-J is obtained for oxygen-rich cool stars. The ability of specific near-infrared indices to separate luminosity classes, atmospheric chemistry or variability subtypes is discussed. Some comments are also given on extinction effects, water band strengths in Long Period Variables and the evaluation of 12CO/13CO ratio in red giants.

  1. Distance scale and variable stars in Local Group Galaxies LMC and Fornax

    CERN Document Server

    Maio, M; Clementini, G; Greco, C; Gullieuszik, M; Held, E V; Poretti, E; Rizzi, L; Bragaglia, A; Carretta, E; Fabrizio, L D; Gratton, R; Taribello, E

    2003-01-01

    We briefly review our photometric and spectroscopic study of RR Lyrae variable stars in the bar of the Large Magellanic Cloud (LMC), that allowed us to reconcile the so-called "short" and "long" distance moduli of the LMC on the value mod_LMC=18.51 +/- 0.085 mag. Then we present preliminary results from the photometric study of a 33' x 34' area in the Fornax dwarf spheroidal galaxy containing the stellar clusters Fornax 3 (NGC 1049) and 6. We identified about 1000 candidate variables in this field of Fornax, and report the first detection and measure of about 60 RR Lyrae variable stars in the globular cluster Fornax 3.

  2. New Variable Stars Discovered as By-product of the Beijing Astronomical Observatory Supernova Survey

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The Beijing Astronomical Observatory (BAO) 0.6 m telescope has been used for nearby supernova survey in more than 3000 fields, covering a total area of 235 deg2. More than 260 000 CCD images have been collected since April 1996, with 45 supernovae discovered. We searched for variables in about 90 000 images taken during 1996-1998. For the fields in which long period variables (LPVs) were discovered, we reduced further images taken from 1999 to 2000, for the period estimation.Among the 280 000 stars selected from the survey fields, i.e., brighter than 18 mag,we discovered seven new LPVs and reconfirmed three known LPVs. Additionally,we found 146 variable star candidates, and reconfirmed about 20 previously known or suspected objects.

  3. Book Review: Light Curves of Variable Stars by C. Sterken and C. Jaschek 1996, Cambridge University Press, ISBN 052190168

    Science.gov (United States)

    van Genderen, A. M.

    Since about the early seventies no proper book on variable stars has been written. The probable reason is the explosive growth of the field of variable-star research during the 25 years since. It was not only the amount of observational data which grew so fast, but also the number of new types of variable stars and the knowledge of the causes of their variability. Variable stars also became of fastly growing importance for distance determinations, for the physics of stellar interiors and for stellar evolution. The two editors, together with seven other experts on variable stars have now found a perfect recipe to write a conveniently-sized book on variable stars. The time was ripe. They compiled a pictorial atlas of at least 200 typical light curves of tens of different kinds of variable stars. The book also gives a clear introduction to the historical background, the photometric systems, the nomenclature and the classifications. Each chapter provides a detailed account of each subclass and gives a concise description of the physical processes responsible for the variations. All specific variables discussed in the text can easily be located with the aid of object-name and subject indexes. The reference list contains about 600 entries, a guarantee that one can access a particular subject quickly and in debt. The quality of the figures and the tables is very good. Very useful is the inclusion of three lists, 'Journal abbreviations', 'Acronyms and abbreviations' and 'Addresses of interest', and of three tables concerning constellation names, Julian dates, and specialized newsletters on variable stars. This unique guide will be absolutely invaluable to students taking courses in variable-star research, as well as for professional and amateur astronomers.

  4. 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

  5. The puzzling new class of variable stars in NGC 3766 : old friend pulsators?

    CERN Document Server

    Salmon, S J A J; Reese, D R; Dupret, M -A; Eggenberger, P

    2014-01-01

    The recent variability survey of the NGC 3766 cluster revealed a considerable number of periodic variable stars in a region of the H-R diagram where no pulsation is expected. This region lies between the instability strips of the delta Scuti and SPB stars. Moreover the periods of the new phenomenon, P~0.1-0.7 d, do not allow to associate it a priori to either of these two types of pulsations. Stars in the NGC 3766 cluster are known as fast rotators with rotational velocities typically larger than half of their critical velocity. Rotation can affect both the geometrical properties and period domain of pulsations. It also alters the apparent stellar luminosity through gravity darkening, effect seldom taken considered in theoretical studies of the rotation-pulsation interaction. We explore if both of these effects are able to deliver a consistent interpretation for the observed properties of the "new variables" in NGC 3766: explaining their presence outside the known instability strips and their variability peri...

  6. Variable stars and stellar populations in Andromeda XXV: III. A central cluster or the galaxy nucleus?

    CERN Document Server

    Cusano, Felice; Clementini, Gisella; Cignoni, Michele; Federici, Luciana; Marconi, Marcella; Ripepi, Vincenzo; Musella, Ilaria; Testa, Vincenzo; Carini, Roberta; Faccini, Marco

    2016-01-01

    We present B and V time-series photometry of Andromeda XXV, the third galaxy in our program on the Andromeda's satellites, that we have imaged with the Large Binocular Cameras of the Large Binocular Telescope. The field of Andromeda XXV is found to contain 63 variable stars, for which we present light curves and characteristics of the light variation (period, amplitudes, variability type, mean magnitudes, etc.). The sample includes 58 RR Lyrae variables (46 fundamental-mode $-$ RRab, and 12 first-overtone $-$RRc, pulsators), three anomalous Cepheids, one eclipsing binary system and one unclassified variable. The average period of the RRab stars ($\\langle Pab \\rangle$ = 0.60 $\\sigma=0.04$ days) and the period-amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of (m-M)$_0$=$24.63\\pm0.17$ mag. The color-magnitude diagram reveals the presence in Andromeda XXV of a single, metal-poo...

  7. Variable Stars in the Field of the Hydra II Ultra-faint Dwarf Galaxy

    Science.gov (United States)

    Vivas, A. Katherina; Olsen, Knut; Blum, Robert; Nidever, David L.; Walker, Alistair R.; Martin, Nicolas F.; Besla, Gurtina; Gallart, Carme; van der Marel, Roeland P.; Majewski, Steven R.; Kaleida, Catherine C.; Muñoz, Ricardo R.; Saha, Abhijit; Conn, Blair C.; Jin, Shoko

    2016-05-01

    We report the discovery of one RR Lyrae star in the ultra-faint satellite galaxy Hydra II based on time series photometry in the g, r and i bands obtained with the Dark Energy Camera at Cerro Tololo Inter-American Observatory, Chile. The association of the RR Lyrae star discovered here with Hydra II is clear because is located at 42\\prime\\prime from the center of the dwarf, well within its half-light radius of 102\\prime\\prime . The RR Lyrae star has a mean magnitude of i=21.30+/- 0.04 which is too faint to be a field halo star. This magnitude translates to a heliocentric distance of 151 ± 8 kpc for Hydra II; this value is ∼ 13% larger than the estimate from the discovery paper based on the average magnitude of several blue horizontal branch star candidates. The new distance implies a slightly larger half-light radius of {76}-10+12 pc and a brighter absolute magnitude of {M}V=-5.1+/- 0.3, which keeps this object within the realm of the dwarf galaxies. A comparison with other RR Lyrae stars in ultra-faint systems indicates similar pulsational properties among them, which are different to those found among halo field stars and those in the largest of the Milky Way satellites. We also report the discovery of 31 additional short period variables in the field of view (RR Lyrae, SX Phe, eclipsing binaries, and a likely anomalous cepheid) which are likely not related with Hydra II.

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

    Science.gov (United States)

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

    2016-11-01

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

  9. Processes in astrophysical fluids. On the occasion of the 60th birthday of Giora Shaviv. Proceedings. International Conference on Astrophysical Fluids: From Atomic Nuclei to Stars and Galaxies, Haifa (Israel), 12 - 15 Jan 1998.

    Science.gov (United States)

    Regev, O.

    1999-04-01

    The following topics were dealt with: nuclear processes, solar neutrino problem, gravity waves and solar neutrino problem, primordial He abundance, radiation processes, fluid dynamics processes, astrophysical jets, advection dominated accretion flows, stellar structure, planetary nebula structure, extrasolar planets, gravitational radiation, interacting binary stars, cataclysmic variables, massive supernovae in binaries, stellar mergers in globular clusters, nova outbursts, extragalactic systems, stellar bars in disk galaxies, Lyman α clouds, massive black holes, quasars, accretion disks, IGM enrichment.

  10. The magnetic field and spectral variability of the He-weak star HR 2949

    CERN Document Server

    Shultz, M; Folsom, C P; Wade, G A; Townsend, R H D; Sikora, J; Grunhut, J; Stahl, O

    2015-01-01

    We analyze a high resolution spectropolarimetric dataset collected for the He-weak B3p IV star HR 2949. The Zeeman effect is visible in the circularly polarized component of numerous spectral lines. The longitudinal magnetic field varies between approximately $-650$ and $+150$ G. The polar strength of the surface magnetic dipole is calculated to be 2.4$^{+0.3}_{-0.2}$ kG. The star has strong overabundances of Fe-peak elements, along with extremely strong overabundances of rare-earth elements; however, He, Al, and S are underabundant. This implies that HR 2949 is a chemically peculiar star. Variability is seen in all photospheric lines, likely due to abundance patches as seen in many Ap/Bp stars. Longitudinal magnetic field variations measured from different spectral lines yield different results, likely a consequence of uneven sampling of the photospheric magnetic field by the abundance patches. Analysis of photometric and spectroscopic data for both HR 2949 and its companion star, HR 2948, suggests a revisio...

  11. The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project

    CERN Document Server

    Geier, S; Heber, U; Schaffenroth, V; Barlow, B N; stensen, R H O; O'Toole, S J; Ziegerer, E; Heuser, C; Maxted, P F L; Gänsicke, B T; Marsh, T R; Napiwotzki, R; Brünner, P; Schindewolf, M; Niederhofer, F

    2015-01-01

    The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to find sdBs with compact companions like massive white dwarfs, neutron stars or black holes. Here we provide classifications, atmospheric parameters and a complete radial velocity (RV) catalogue containing 1914 single measurements for an sample of 177 hot subluminous stars discovered based on SDSS DR7. 110 stars show significant RV variability, while 67 qualify as candidates. We constrain the fraction of close massive compact companions {of hydrogen-rich hot subdwarfs} in our sample to be smaller than $\\sim1.3\\%$, which is already close to the theoretical predictions. However, the sample might still contain such binaries with longer periods exceeding $\\sim8\\,{\\rm d}$. We detect a mismatch between the $\\Delta RV_{\\rm max}$-distribution of the sdB and the more evolved sdOB and sdO stars, which challenges our understanding of their evolutionary connection. Furthermore, irregular RV variations of unknown origin with ...

  12. High resolution spectroscopy of bright subdwarf B stars - I. Radial velocity variables

    CERN Document Server

    Edelmann, H; Altmann, M; Karl, C; Lisker, T

    2005-01-01

    Radial velocity curves for 15 bright subdwarf B binary systems have been measured using high precision radial velocity measurements from high S/N optical high-resolution spectra. In addition, two bright sdB stars are discovered to be radial velocity variable but the period could not yet be determined. The companions for all systems are unseen. The periods range from about 0.18 days up to more than ten days. The radial velocity semi amplitudes are found to lie between 15 and 130 km/s. Using the mass functions, the masses of the unseen companions have been constrained to lower limits of 0.03 up to 0.55 M_sun, and most probable values of 0.03 up to 0.81 M_sun. The invisible companions for three of our program stars are undoubtedly white dwarfs. In the other cases they could be either white dwarfs or main sequence stars. For two stars the secondaries could possibly be brown dwarfs. As expected, the orbits are circular for most of the systems. However, for one third of the program stars we find slightly eccentric ...

  13. The molecular gas around the luminous blue variable star G24.73+0.69

    CERN Document Server

    Petriella, A; Giacani, E

    2011-01-01

    AIMS: We study the molecular environment of the luminous blue variable star G24.73+0.69 to investigate the origin of the two infrared shells around this massive star and to determine its effects on the surrounding interstellar medium. METHODS: We analyze the distribution of the molecular gas using the 13CO J=1-0 emission extracted from the Galactic Ring Survey. We also use near and mid-infrared data from 2MASS and GLIMPSE to identify the young stellar objects in the field. RESULTS: We discover the molecular counterpart of the outer infrared shell around G24.73+0.69. The CO shell was probably blown by the stellar wind of the star mainly during its main sequence phase. We also find molecular gas in correspondence with the inner infrared shell, although its origin remains uncertain. We find seven young stellar objects upon the molecular material, whose birth could have been triggered by the stellar wind of the luminous blue variable star. We suggest that G24.73+0.69 and the progenitor of the nearby supernova rem...

  14. The variability behavior of CoRoT M-giant Stars

    CERN Document Server

    Lopes, C E Ferreira; Leão, I C; de Freitas, D B; Martins, B L Canto; da Costa, A D; Paz-Chinchón, F; Chagas, M L Das; Baglin, A; Janot-Pacheco, E; De Medeiros, J R

    2015-01-01

    For 6 years the Convection, Rotation, and Planetary Transits (CoRoT) space mission has acquired photometric data from more than one hundred thousand point sources towards and directly opposite from the inner and outer regions of the Galaxy. The high temporal resolution of the CoRoT data combined with the wide time span of the observations has enabled the study of short and long time variations in unprecedented detail. From the initial sample of 2534 stars classified as M-giants in the CoRoT databasis, we selected 1428 targets that exhibit well defined variability, using visual inspection. The variability period and amplitude of C1 stars (stars having Teff < 4200 K) were computed using Lomb-Scargle and harmonic fit methods. The trends found in the V-I vs J-K color-color diagram are in agreement with standard empirical calibrations for M-giants. The sources located towards the inner regions of the Galaxy are distributed throughout the diagram while the majority of the stars towards the outer regions of the G...

  15. Low-Amplitude Variables: Distinguishing RR Lyrae stars from Eclipsing Binaries

    CERN Document Server

    Kinman, T D

    2010-01-01

    It is not easy to identify and classify low-amplitude variables, but it is important that the classification is done correctly. We use photometry and spectroscopy to classify low-amplitude variables in a 246 deg^2 part of the Akerlof et al. (2002) field. Akerlof and collaborators found that 38% of the RR Lyrae stars in their 2000 deg^2 test field were RR1 (type c). This suggests that these RR Lyrae stars belong to an Oosterhoff Type II population while their period distribution is primarily Oosterhoff Type I. Our observations support their RR0 (type ab) classifications, however 6 of the 7 stars that they classified as RR1 (type c) are eclipsing binaries. Our classifications are supported by spectroscopic metallicities, line-broadening and Galactic rotation measurements. Our 246 deg^2 field contains 16 RR Lyrae stars that are brighter than m_R = 14.5; only four of these are RR1 (type c). This corresponds to an Oosterhoff Type I population in agreement with the period distribution.

  16. New variable stars discovered in the fields of three Galactic open clusters using the VVV Survey

    CERN Document Server

    Palma, Tali; Dékány, Istvan; Clariá, Juan J; Alonso-García, Javier; Gramajo, Luciana V; Alegría, Sebastian Ramírez; Bonatto, Charles

    2016-01-01

    This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the $J$-, $H$- and $K_s$- bands obtained from the Vista Variables in the V\\'ia L\\'actea (VVV) Survey. We performed in each cluster field a variability search using Stetson's variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study, 157 in total in three different known OCs, are classified based on their light curve shapes, periods, amplitudes and their location in the corresponding color-magnitude $(J-K_s,K_s)$ and color-color $(H-K_s,J-H)$ diagrams. We found 5 possible Cepheid stars which, based on the period-luminosity rel...

  17. Search for transiting exoplanets and variable stars in the open cluster NGC 7243

    CERN Document Server

    Garai, Z; Hambálek, L; Errmann, R; Adam, Ch; Buder, S; Butterley, T; Dhillon, V S; Dincel, B; Gilbert, H; Ginski, Ch; Hardy, L K; Kellerer, A; Kitze, M; Kundra, E; Littlefair, S P; Mugrauer, M; Nedoroščík, J; Neuhäuser, R; Pannicke, A; Raetz, S; Schmidt, J G; Schmidt, T O B; Seeliger, M; Vaňko, M; Wilson, R W

    2016-01-01

    We report results of the first five observing campaigns for the open stellar cluster NGC 7243 in the frame of project Young Exoplanet Transit Initiative (YETI). The project focuses on the monitoring of young and nearby stellar clusters, with the aim to detect young transiting exoplanets, and to study other variability phenomena on time-scales from minutes to years. After five observing campaigns and additional observations during 2013 and 2014, a clear and repeating transit-like signal was detected in the light curve of J221550.6+495611. Furthermore, we detected and analysed 37 new eclipsing binary stars in the studied region. The best fit parameters and light curves of all systems are given. Finally, we detected and analysed 26 new, presumably pulsating variable stars in the studied region. The follow-up investigation of these objects, including spectroscopic measurements of the exoplanet candidate, is currently planned.

  18. VizieR Online Data Catalog: Updated catalog of variable stars in globular clusters (Clement+ 2017)

    Science.gov (United States)

    Clement, C. M.

    2017-02-01

    This Catalogue is an update to Helen Sawyer Hogg's Third Catalogue on Variable Stars in Globular Clusters (1973, David Dunlap Observatory Publications, Volume 3, Number 6: 1973PDDO....3....6S; see Cat V/97; see also Clement+, 2001AJ....122.2587C). This catalogue is based on the individual cluster files downloaded on http://www.astro.utoronto.ca/~cclement/cat/listngc.html on the 01-Feb-2017. (7 data files).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-04-15

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

  20. The supergiant B[e] star LHA 115-S 18 - binary and/or luminous blue variable?

    CERN Document Server

    Clark, J S; Coe, M J; Dorda, R; Haberl, F; Lamb, J B; Negueruela, I; Udalski, A

    2013-01-01

    The mechanism by which supergiant (sg)B[e] stars support cool, dense dusty discs/tori and their physical relationship with other evolved, massive stars such as luminous blue variables is uncertain. In order to investigate both issues we have analysed the long term behaviour of the canonical sgB[e] star LHA 115-S 18. We employed the OGLE II-IV lightcurve to search for (a-)periodic variability and supplemented these data with new and historic spectroscopy. In contrast to historical expectations for sgB[e] stars, S18 is both photometrically and spectroscopically highly variable. The lightcurve is characterised by rapid aperiodic `flaring' throughout the 16 years of observations. Changes in the high excitation emission line component of the spectrum imply evolution in the stellar temperature - as expected for luminous blue variables - although somewhat surprisingly, spectroscopic and photometric variability appears not to be correlated. Characterised by emission in low excitation metallic species, the cool circum...

  1. Ultraviolet and visual flux and line variations of one of the least variable Bp stars HD 64740

    CERN Document Server

    Krticka, J; Markova, H; Mikulasek, Z; Zverko, J; Prvak, M; Skarka, M

    2013-01-01

    The light variability of hot magnetic chemically peculiar stars is typically caused by the flux redistribution in spots with peculiar abundance. This raises the question why some stars with surface abundance spots show significant rotational light variability, while others do not. We study the Bp star HD 64740 to investigate how its remarkable inhomogeneities in the surface distribution of helium and silicon, and the corresponding strong variability of many spectral lines, can result in one of the faintest photometric variabilities among the Bp stars. We used model atmospheres and synthetic spectra calculated for the silicon and helium abundances from surface abundance maps to predict the ultraviolet and visual light and line variability of HD 64740. The predicted fluxes and line profiles were compared with the observed ones derived with the IUE, HST, and Hipparcos satellites and with spectra acquired using the FEROS spectrograph at the 2.2m MPG/ESO telescope. We are able to reproduce the observed visual ligh...

  2. Short period variable stars recognition by using MVA methods in Pi of the Sky experiment

    Science.gov (United States)

    Obara, L.

    2016-12-01

    Pi of the Sky is a system of wide field-of-view robotic telescopes to search for short timescale astrophysical phenomena, especially for prompt optical GRB emission. The system was designed for autonomous operation, monitoring a large fraction of the sky with limit magnitude in the range 12m-13m and time resolution on the order of 1-100 seconds. LUIZA is a dedicated framework developed for efficient off-line processing of the Pi of the Sky data, implemented in C++. The photometric algorithm based on the All Sky Automated Survey (ASAS) photometry was implemented in LUIZA and compared with the algorithm based on the pixel cluster reconstruction and simple aperture photometry algorithm. Optimized photometry algorithms were then applied to the sample of test images, which were modified to include different patterns of variability of the stars in training sample. Different statistical estimators were considered for developing the general variable star identification algorithm. The algorithm will be used to search for short-period variable stars in real data.

  3. Searching the short-period variable stars with the photometric algorithm implemented in LUIZA framework

    Science.gov (United States)

    Obara, Lukasz; Żarnecki, Aleksander Filip

    2015-09-01

    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 GRB emission. 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. LUIZA is a dedicated framework developed for efficient off-line processing of the Pi of the Sky data, implemented in C++. The photometric algorithm based on ASAS photometry was implemented in LUIZA and compared with the algorithm based on the pixel cluster reconstruction and simple aperture photometry algorithm. Optimized photometry algorithms were then applied to the sample of test images, which were modified to include different patterns of variability of the stars (training sample). Different statistical estimators are considered for developing the general variable star identification algorithm. The algorithm will then be used to search for short-period variable stars in the real data.

  4. YSOVAR: Mid-infrared Variability Among YSOs in the Star Formation Region GGD 12-15

    CERN Document Server

    Wolk, Scott J; Poppenhaeger, Katja; Cody, A M; Rebull, L M; Forbrich, J; Gutermuth, R A; Hillenbrand, L A; Plavchan, P; Stauffer, J R; Covey, K R; Song, Inseok

    2015-01-01

    We present an IR-monitoring survey with the $Spitzer$ Space Telescope of the star forming region GGD 12-15. Over 1000 objects were monitored including about 350 objects within the central 5 arcminutes 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 (YSOVAR) project. The region was also the subject of a contemporaneous 67ks $Chandra$ 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 arcminutes are young stellar objects 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-IR variability. There are 39 periodic sources, all but one of these is found to be a cluster member. Almost half of t...

  5. 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...... missions, are capable of identifying the most common types of stellar variability in a reliable way. Many new variables have been discovered, among which a large fraction are eclipsing/ellipsoidal binaries unknown prior to launch. A comparison is made between our classification from the Kepler data...

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

    CERN Document Server

    Rivinius, Thomas; Carciofi, Alex

    2016-01-01

    Context: [abbreviated] 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: [abbreviated] 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 \\v{S}tefl fre...

  7. 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.

  8. Statistically Optimal Approximations of Astronomical Signals: Implications to Classification and Advanced Study of Variable Stars

    Science.gov (United States)

    Andronov, I. L.; Chinarova, L. L.; Kudashkina, L. S.; Marsakova, V. I.; Tkachenko, M. G.

    2016-06-01

    We have elaborated a set of new algorithms and programs for advanced time series analysis of (generally) multi-component multi-channel observations with irregularly spaced times of observations, which is a common case for large photometric surveys. Previous self-review on these methods for periodogram, scalegram, wavelet, autocorrelation analysis as well as on "running" or "sub-interval" local approximations were self-reviewed in (2003ASPC..292..391A). For an approximation of the phase light curves of nearly-periodic pulsating stars, we use a Trigonometric Polynomial (TP) fit of the statistically optimal degree and initial period improvement using differential corrections (1994OAP.....7...49A). For the determination of parameters of "characteristic points" (minima, maxima, crossings of some constant value etc.) we use a set of methods self-reviewed in 2005ASPC..335...37A, Results of the analysis of the catalogs compiled using these programs are presented in 2014AASP....4....3A. For more complicated signals, we use "phenomenological approximations" with "special shapes" based on functions defined on sub-intervals rather on the complete interval. E. g. for the Algol-type stars we developed the NAV ("New Algol Variable") algorithm (2012Ap.....55..536A, 2012arXiv1212.6707A, 2015JASS...32..127A), which was compared to common methods of Trigonometric Polynomial Fit (TP) or local Algebraic Polynomial (A) fit of a fixed or (alternately) statistically optimal degree. The method allows determine the minimal set of parameters required for the "General Catalogue of Variable Stars", as well as an extended set of phenomenological and astrophysical parameters which may be used for the classification. Totally more that 1900 variable stars were studied in our group using these methods in a frame of the "Inter-Longitude Astronomy" campaign (2010OAP....23....8A) and the "Ukrainian Virtual Observatory" project (2012KPCB...28...85V).

  9. The UK Infrared Telescope M33 monitoring project. IV. Variable red giant stars across the galactic disc

    CERN Document Server

    Javadi, Atefeh; van Loon, Jacco Th; Khosroshahi, Habib; Golabatooni, Najmeh; Mirtorabi, Mohammad Taghi

    2014-01-01

    We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. In this fourth paper of the series, we present a search for variable red giant stars in an almost square degree region comprising most of the galaxy's disc, carried out with the WFCAM instrument in the K band. These data, taken during the period 2005--2007, were complemented by J- and H-band images. Photometry was obtained for 403 734 stars in this region; of these, 4643 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. The variable stars are concentrated towards the centre of M33, more so than low-mass, less-evolved red giants. Our data were matched to optical catalogues of variable stars and ca...

  10. Possible candidates for multiple occurrence of variable stars in the VSX catalogue

    CERN Document Server

    Liska, Jiri; Auer, Reinhold Friedrich; Prudil, Zdenek; Juranova, Anna

    2015-01-01

    A paper about variable stars with possible multiple occurrence in the VSX catalogue is presented. Our main criteria for identification of such duplicities were the angular distance among stars (below 1 arcmin) and close periods of objects. In our approach, we also considered double or half values of periods to reveal possible misclassification among stars with similar light curve shapes. The probability of false identification is expressed by the parameter R giving the relative difference between periods. We found 1487 pairs of stars in angular distance lower than 1 arcmin with period difference R lower than 0.1 %, which are high-probable candidates on duplicates. From this sample, 354 pairs have exactly the same periods (R = 0.0 %) and should be considered as definite duplicates. The main contribution of certain duplicates comes from the Catalina Sky Survey (73 pairs have two names with CSS acronym) and from the BEST projects (71 pairs). Distribution of identified duplicates on the sky is not homogeneous but...

  11. Time-resolved multicolour photometry of bright B-type variable stars in Scorpius

    CERN Document Server

    Handler, G

    2013-01-01

    The first two of a total of six nano-satellites that will constitute the BRITE-Constellation space photometry mission have recently been launched successfully. In preparation for this project, we carried out time-resolved colour photometry in a field that is an excellent candidate for BRITE measurements from space. We acquired 117 h of Stromgren uvy data during 19 nights. Our targets comprised the Beta Cephei stars Kappa and Lambda Sco, the eclipsing binary Mu 1 Sco, and the variable super/hypergiant Zeta 1 Sco. For Kappa Sco, a photometric mode identification in combination with results from the spectroscopic literature suggests a dominant (l, m) = (1, -1) Beta Cephei-type pulsation mode of the primary star. The longer period of the star may be a rotational variation or a g-mode pulsation. For Lambda Sco, we recover the known dominant Beta Cephei pulsation, a longer-period variation, and observed part of an eclipse. Lack of ultraviolet data precludes mode identification for this star. We noticed that the spe...

  12. Link between Mass-loss and Variability Type for AGB Stars?

    CERN Document Server

    Ivezic, Z; Ivezic, Zeljko; Knapp, Gillian R.

    1998-01-01

    We find that AGB stars separate in the 25-12 vs. 12-K color-color diagram according to their chemistry (O, S vs. C) and variability type (Miras vs. SRb/Lb). While discrimination according to the chemical composition is not surprising, the separation of Miras from SRb/Lb variables is unexpected. We show that ``standard'' steady-state radiatively driven models provide excellent fits to the color distribution of Miras of all chemical types. However, these models are incapable of explaining the dust emission from O-rich SRb/Lb stars. The models can be altered to fit the data by postulating different optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300-400 K) than typical condensation temperatures (800-1000 K), a possibility which is also supported by the detailed characteristics of LRS data. The absence of hot dust for SRb/Lb stars can be interpreted as a recent (order of 100 yr) decrease in the mass-loss rate. The distribution o...

  13. The OmegaWhite Survey for Short-Period Variable Stars I: Overview and First Results

    CERN Document Server

    Macfarlane, S A; Ramsay, G; Groot, P J; Woudt, P A; Drew, J E; Barentsen, G; Eisloffel, J

    2015-01-01

    We present the goals, strategy and first results of the OmegaWhite survey: a wide-field high-cadence $g$-band synoptic survey which aims to unveil the Galactic population of short-period variable stars (with periods $<$ 80 min), including ultracompact binary star systems and stellar pulsators. The ultimate goal of OmegaWhite is to cover 400 square degrees along the Galactic Plane reaching a depth of $g = $ 21.5 mag (10$\\sigma$), using OmegaCam on the VLT Survey Telescope (VST). The fields are selected to overlap with surveys such as the Galactic Bulge Survey (GBS) and the VST Photometric H$\\alpha$ Survey of the Southern Galactic Plane (VPHAS+) for multi-band colour information. Each field is observed using 38 exposures of 39 s each, with a median cadence of $\\sim$2.7 min for a total duration of two hours. Within an initial 26 square degrees, we have extracted the light curves of 1.6 million stars, and have identified 613 variable candidates which satisfy our selection criteria. Furthermore, we present the ...

  14. The Hypervelocity Star SDSS J090745.0+024507 is a Short-Period Variable

    CERN Document Server

    Fuentes, C I; Gaudi, B S; McLeod, B A; Bogdanov, S B; Hartman, J D; Hickox, R C; Holman, M J; Fuentes, Cesar I.; Leod, Brian A. Mc; Bogdanov, Slavko B.; Hartman, Joel D.; Hickox, Ryan C.; Holman, Matthew J.

    2005-01-01

    We present high-precision photometry of the hypervelocity star SDSS J090745.0+024507 (HVS), which has a Galactic rest-frame radial velocity of v=709 km/s, and so has likely been ejected from the supermassive black hole in the Galactic center. Our data were obtained on two nights using the MMT 6.5m telescope, and is supplemented by lower precision photometry obtained on four nights using the FLWO 1.2m telescope. The high-precision photometry indicates that the HVS is a short-period, low-amplitude variable, with period P=0.2-2 days and amplitude A = 2-10%. Together with the known effective temperature of T_eff ~ 10,500 K (spectral type B9), this variability implies that the HVS is a member of the class of slowly pulsating B-type main sequence stars, thus resolving the previously-reported two-fold degeneracy in the luminosity and distance of the star. The HVS has a heliocentric distance of 71 kpc, and an age of ~0.35 Gyr. The time of ejection from the center of the Galaxy is < 100 Myr, and thus the existence ...

  15. The Variable Star Population of the Globular Cluster B514 in the Andromeda Galaxy

    CERN Document Server

    Clementini, Gisella; Federici, Luciana; Cacciari, Carla; Merighi, Roberto; Smith, Horace A; Catelan, Marcio; Pecci, Flavio Fusi; Marconi, Marcella; Kinemuchi, Karen; Pritzl, Barton J

    2009-01-01

    A rich harvest of RR Lyrae stars has been identified for the first time in B514, a metal-poor ([Fe/H] = 1.95 +/- 0.10 dex) globular cluster of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Camera for Surveys time-series observations. We have detected and derived periods for 89 RR Lyrae stars (82 fundamental-mode -RRab- and 7 first-overtone -RRc- pulsators, respectively) among 161 candidate variables identified in the cluster. The average period of the RR Lyrae variables ( = 0.58 days and = 0.35 days, for RRab and RRc pulsators, respectively) and the position in the period-amplitude diagram both suggest that B514 is likely an Oosterhoff type I cluster. This appears to be in disagreement with the general behaviour of the metal-poor globular clusters in the Milky Way, which show instead Oosterhoff type II pulsation properties. The average apparent magnitude of the RR Lyrae stars sets the mean level of the cluster horizontal branch at = 25.18 +/- 0.02 (si...

  16. Variable Stars in Leo A RR Lyraes, Short-period Cepheids, and Implications on Stellar Content

    CERN Document Server

    Dolphin, A E; Claver, J; Skillman, E D; Cole, A A; Gallagher, J S; Tolstoy, E; Dohm-Palmer, R C; Mateo, M

    2002-01-01

    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 Lyraes, we measure a distance modulus of (m-M)_0 = 24.51 +/- 0.12, or 0.80 +/- 0.04 Mpc. This discovery of RR Lyraes confirms, for the first time, the presence of an ancient (> ~11 Gyr) population in Leo A accounting for at least 0.1% of the galaxy's V luminosity. We have also discovered a halo of old (> ~2 Gyr) stars surrounding Leo A, with a scale length roughly 50% larger than that of the dominant young population. We also report the discovery of a large population of Cepheids in Leo A. The median absolute magnitude of our Cepheid sample is M_V = -1.1, fainter than 96% of SMC and 99% of LMC Cepheids. Their periods are also unusual, with three Cepheids that are deduced to be pulsating in the fundamental mode having periods of under 1 day. Upon examination, these characteristics of the Leo A Cepheid population appear to be a natural extension...

  17. On the interpretation of new late B- and early A-type periodic variable stars in NGC 3766

    CERN Document Server

    Mowlavi, N; Barblan, F; Eyer, L

    2013-01-01

    We investigate possible interpretations of the new periodic B- and A-type variable stars discovered in NGC 3766. They lie in the region of the Hertzsprung-Russell diagram between slowly pulsating B and delta Sct stars, a region where no pulsation is predicted by standard models of pulsating stars. We show that the two other possible causes of periodic light curve variations, rotational modulation and binarity, cannot provide a satisfactory explanation for all the properties observed in those stars either. The question of their origin is thus currently an open issue.

  18. 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.

  19. Photometry of Variable Stars from Dome A, Antarctica: Results from the 2010 Observing Season

    CERN Document Server

    Wang, Lingzhi; Wang, Lifan; Ashley, Michael C B; Cui, Xiangqun; Feng, Long-Long; Gong, Xuefei; Lawrence, Jon S; Liu, Qiang; Luong-Van, Daniel; Pennypacker, Carl R; Shang, Zhaohui; Storey, John W V; Yang, Huigen; Yang, Ji; Yuan, Xiangyan; York, Donald G; Zhou, Xu; Zhu, Zhenxi; Zhu, Zonghong

    2013-01-01

    We present results from a season of observations with the Chinese Small Telescope ARray (CSTAR), obtained over 183 days of the 2010 Antarctic winter. We carried out high-cadence time-series aperture photometry of 20,000 stars with i<15.3 mag located in a 23 square-degree region centered on the south celestial pole. We identified 188 variable stars, including 67 new objects relative to our 2008 observations, thanks to broader synoptic coverage, a deeper magnitude limit and a larger field of view. We used the photometric data set to derive site statistics from Dome A. Based on two years of observations, we find that extinction due to clouds at this site is less than 0.1 and 0.4 mag during 45% and 75% of the dark time, respectively.

  20. LS Peg A Low-Inclination SW Sextantis-Type Cataclysmic Binary with High-Velocity Balmer Emission Line Wings

    CERN Document Server

    Taylor, C J; Patterson, J

    1998-01-01

    We present time-resolved spectroscopy and photometry of the bright cataclysmic variable LS Peg (= S193). The Balmer lines exhibit broad, asymmetric wings Doppler-shifted by about 2000 km/s at the edges, while the HeI lines show phase-dependent absorption features strikingly similar to SW Sextantis stars, as well as emission through most of the phase. The CIII/NIII emission blend does not show any phase dependence. From velocities of Halpha emission lines, we determine an orbital period of 0.174774 +/- 0.000003 d (= 4.1946 h), which agrees with Szkody's (1995) value of approximately 4.2 hours. No stable photometric signal was found at the orbital period. A non-coherent quasi-periodic photometric signal was seen at a period of 20.7 +/- 0.3 min. The high-velocity Balmer wings most probably arise from a stream re-impact point close to the white dwarf. We present simulated spectra based on a kinematic model similar to the modified disk-overflow scenario of Hellier & Robinson (1994). The models reproduce the br...

  1. Theory review: Line-driven instability and other causes of structure and variability in hot-star winds

    Science.gov (United States)

    Owocki, Stanley P.

    1994-01-01

    The winds of the hot, luminous, OB stars are driven by the line-scattering of the star's continuum radiation flux. Several kinds of observational evidence indicate that such winds are highly structured and variable. This paper will review possible theoretical causes of such wind structure. For relatively small-scale, stochastic variability, I review the role of the strong intrinsic instability of the line-driving process itself. for larger scale structure, I describe recent efforts to examine how disturbances from the underlying, rotating star can be translated outward into propagating features in the wind.

  2. Laboratory analogue of a supersonic accretion column in a binary star system

    Science.gov (United States)

    Cross, J. E.; Gregori, G.; Foster, J. M.; Graham, P.; Bonnet-Bidaud, J. -M.; Busschaert, C.; Charpentier, N.; Danson, C. N.; Doyle, H. W.; Drake, R. P.; Fyrth, J.; Gumbrell, E. T.; Koenig, M.; Krauland, C.; Kuranz, C. C.; Loupias, B.; Michaut, C.; Mouchet, M.; Patankar, S.; Skidmore, J.; Spindloe, C.; Tubman, E. R.; Woolsey, N.; Yurchak, R.

    2016-01-01

    Astrophysical flows exhibit rich behaviour resulting from the interplay of different forms of energy—gravitational, thermal, magnetic and radiative. For magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (B>10 MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100–1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions. PMID:27291065

  3. Laboratory analogue of a supersonic accretion column in a binary star system.

    Science.gov (United States)

    Cross, J E; Gregori, G; Foster, J M; Graham, P; Bonnet-Bidaud, J-M; Busschaert, C; Charpentier, N; Danson, C N; Doyle, H W; Drake, R P; Fyrth, J; Gumbrell, E T; Koenig, M; Krauland, C; Kuranz, C C; Loupias, B; Michaut, C; Mouchet, M; Patankar, S; Skidmore, J; Spindloe, C; Tubman, E R; Woolsey, N; Yurchak, R; Falize, É

    2016-06-13

    Astrophysical flows exhibit rich behaviour resulting from the interplay of different forms of energy-gravitational, thermal, magnetic and radiative. For magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (B>10 MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100-1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions.

  4. A near-infrared interferometric survey of debris-disc stars. V. PIONIER search for variability

    CERN Document Server

    Ertel, S; Absil, O; Bouquin, J -B Le; Augereau, J -C; Berger, J -P; Blind, N; Bonsor, A; Lagrange, A -M; Lebreton, J; Marion, L; Milli, J; Olofsson, J

    2016-01-01

    Context: Extended circumstellar emission has been detected within a few 100 milli-arcsec around > 10% of nearby main sequence stars using near-infrared interferometry. Follow-up observations using other techniques, should they yield similar results or non-detections, can provide strong constraints on the origin of the emission. They can also reveal the variability of the phenomenon. Aims: We aim to demonstrate the persistence of the phenomenon over time scales of a few years and to search for variability of our previously detected excesses. Methods: Using VLTI/PIONIER in H band we have carried out multi-epoch observations of the stars for which a near-infrared excess was previously detected with the same observing technique and instrument. The detection rates and distribution of the excesses from our original survey and the follow-up observations are compared statistically. A search for variability of the excesses in our time series is carried out based on the level of the broadband excesses. Results: In 12 o...

  5. Revisiting the variable star population in NGC~6229 and the structure of the Horizontal Branch

    CERN Document Server

    Ferro, A Arellano; Bramich, D M; Giridhar, S; Ahumada, J A; Kains, N; Kuppuswamy, K

    2015-01-01

    We report an analysis of new $V$ and $I$ CCD time-series photometry of the distant globular cluster NGC 6229. The principal aims were to explore the field of the cluster in search of new variables, and to Fourier decompose the RR Lyrae light curves in pursuit of physical parameters.We found 25 new variables: 10 RRab, 5 RRc, 6 SR, 1 CW, 1 SX Phe, and two that we were unable to classify. Secular period changes were detected and measured in some favourable cases. The classifications of some of the known variables were rectified. The Fourier decomposition of RRab and RRc light curves was used to independently estimate the mean cluster value of [Fe/H] and distance. From the RRab stars we found [Fe/H]$_{\\rm UVES}$=$-1.31 \\pm 0.01{\\rm(statistical)} \\pm 0.12{\\rm(systematic)}$ ([Fe/H]$_{\\rm ZW}=-1.42$),and a distance of $30.0\\pm 1.5$ kpc, and from the RRc stars we found [Fe/H]$_{\\rm UVES}$=$-1.29\\pm 0.12$ and a distance of $30.7\\pm 1.1$ kpc, respectively. Absolute magnitudes, radii and masses are also reported for ind...

  6. H α profile variabilities in the spectrum of the star WW Vul in 2006-2010

    Science.gov (United States)

    Medzhidova, S. O.; Mikailov, Kh. M.; Rustamov, B. N.

    2014-06-01

    We present the results of our studies of the H α line in the spectrum of a UX Ori star (WW Vul) based on our spectroscopic observations performed with the 2-m telescope at the Shamakhi Astrophysical Observatory, the National Academy of Sciences of Azerbaijan, in 2006-2010. We have detected variability in all the measured parameters of the H α profile both during each observing season and from season to season. A comparative analysis of our data and published studies has led to the conclusion that the regime of outflow with a variable power in the star WW Vul, on the whole, is preserved for almost 40 years (1972-2010) and the accretion of gas from the circumstellar disk onto the stellar surface is occasionally observed. Changes in the regime of variability in the behavior of the H α emission line have been revealed in the 2006-2010 observing seasons. In four cases (for July 8, 2006, August 17, 2008, June 13, 2010, and August 2, 2010), we have detected a second emission component in the blue wing of the H α emission line.

  7. Magnetic Flux of Progenitor Stars Sets Gamma-ray Burst Luminosity and Variability

    CERN Document Server

    Tchekhovskoy, Alexander

    2014-01-01

    Long-duration gamma-ray bursts (GRBs) are thought to come from the core-collapse of Wolf-Rayet stars. Whereas their stellar masses $M_*$ have a rather narrow distribution, the population of GRBs is very diverse, with gamma-ray luminosities $L_\\gamma$ spanning several orders of magnitude. This suggests the existence of a "hidden" stellar variable whose burst-to-burst variation leads to a spread in $L_\\gamma$. Whatever this hidden variable is, its variation should not noticeably affect the shape of GRB lightcurves, which display a constant luminosity (in a time-average sense) followed by a sharp drop at the end of the burst seen with Swift/XRT. We argue that such a hidden variable is progenitor star's large-scale magnetic flux. Shortly after the core collapse, most of stellar magnetic flux accumulates near the black hole (BH) and remains there. The flux extracts BH rotational energy and powers jets of roughly a constant luminosity, $L_j$. However, once BH mass accretion rate $\\dot M$ falls below $\\sim L_j/c^2$,...

  8. Variability in young very low mass stars: Two surprises from spectrophotometric monitoring

    CERN Document Server

    Bozhinova, I; Eislöffel, J

    2016-01-01

    We present simultaneous photometric and spectroscopic observations of seven young and highly variable M dwarfs in star forming regions in Orion, conducted in 4 observing nights with FORS2 at ESO/VLT. All seven targets show significant photometric variability in the I-band, with amplitudes between 0.1-0.8 mag, The spectra, however, remain remarkably constant, with spectral type changes less than 0.5 subtypes. Thus, the brightness changes are not caused by veiling that 'fills in' absorption features. Three objects in the $\\sigma$ Ori cluster (age $\\sim$3 Myr) exhibit strong H$\\alpha$ emission and H$\\alpha$ variability, in addition to the continuum variations. Their behaviour is mostly consistent with the presence of spots with temperature of $\\sim300$ K above the photosphere and filling factors between 0.2-0.4, in contrast to typical hot spots observed in more massive stars. The remaining targets near $\\epsilon$ Ori, likely to be older, show eclipse-like lightcurves, no significant H$\\alpha$ activity and are be...

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

    CERN Document Server

    Ramsay, Gavin; Doyle, J Gerry

    2015-01-01

    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 mins was 58.5 hrs, with additional data with lower cadence. We test for photometric variability using the Kruskal-Wallis H-test and find that 4 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 percent). No flares were detected from any source. The percentage of sources which we found were variable is similar to previous studies. We summarise the mechanisms which have been put forward to explain the light curves of brown dwarfs.

  10. Multicolor CCD Photometry and Period Analysis of Three Pulsating Variable Stars

    Science.gov (United States)

    Alton, K. B.

    2014-06-01

    Multicolor CCD photometry of three pulsating variable stars, RR Leo, TYC 790-1124-1, and V337 Ori has lead to period solutions using Fourier methods on light curves acquired at UnderOak Observatory (UO). New photometric data from RR Leo largely corroborate findings previously reported for this well studied RRab variable. An O-C diagram period analysis using a rich historical record of time-of-maximum light data produced an updated quadratic ephemeris for RR Leo. Although not compelling, underlying sinusoidal variability in the quadratic residuals suggest that this intrinsic variable may also have a gravitationally bound cohort. Light curves from the poorly studied HADS variable TYC 790-1124-1 were remarkably symmetrical; this behavior was observed during a single campaign in 2011 which lasted only one month. Fortunately, starting nearly a decade ago photometric data were also captured by the ASAS survey between 2002 and 2009; the combined results reveal that the fundamental period and light curve shape for TYC 790-1124-1 has substantively remained unchanged. V337 Ori has only been studied by two other investigative groups within the past three years; their results and the two most prominent pulsation frequencies at 4.96877 and 6.72 c/d detected in the UO light curves are in good agreement. Notably this HADS exhibits significant cycle-to-cycle amplitude variability which may be related to these and other pulsation modes not detected in the present study.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-20

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

  12. A near-infrared interferometric survey of debris-disc stars. V. PIONIER search for variability

    Science.gov (United States)

    Ertel, S.; Defrère, D.; Absil, O.; Le Bouquin, J.-B.; Augereau, J.-C.; Berger, J.-P.; Blind, N.; Bonsor, A.; Lagrange, A.-M.; Lebreton, J.; Marion, L.; Milli, J.; Olofsson, J.

    2016-10-01

    Context. Extended circumstellar emission has been detected within a few 100 milli-arcsec around ≳10% of nearby main sequence stars using near-infrared interferometry. Follow-up observations using other techniques, should they yield similar results or non-detections, can provide strong constraints on the origin of the emission. They can also reveal the variability of the phenomenon. Aims: We aim to demonstrate the persistence of the phenomenon over the timescale of a few years and to search for variability of our previously detected excesses. Methods: Using Very Large Telescope Interferometer (VLTI)/Precision Integrated Optics Near Infrared ExpeRiment (PIONIER) in H band we have carried out multi-epoch observations of the stars for which a near-infrared excess was previously detected using the same observation technique and instrument. The detection rates and distribution of the excesses from our original survey and the follow-up observations are compared statistically. A search for variability of the excesses in our time series is carried out based on the level of the broadband excesses. Results: In 12 of 16 follow-up observations, an excess is re-detected with a significance of > 2σ, and in 7 of 16 follow-up observations significant excess (> 3σ) is re-detected. We statistically demonstrate with very high confidence that the phenomenon persists for the majority of the systems. We also present the first detection of potential variability in two sources. Conclusions: We conclude that the phenomenon responsible for the excesses persists over the timescale of a few years for the majority of the systems. However, we also find that variability intrinsic to a target can cause it to have no significant excess at the time of a specific observation. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 088.C-0266, 089.C-0365, 090.C-0526, 091.C-0576, 091.C-0597, 094.C-0232, and commissioning data.

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

    Directory of Open Access Journals (Sweden)

    Camila Dalben Madeira Campos

    2012-06-01

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

  14. Relating jet structure to photometric variability: the Herbig Ae star HD 163296

    CERN Document Server

    Ellerbroek, L E; Dougados, C; Cabrit, S; Sitko, M L; Sana, H; Kaper, L; de Koter, A; Klaassen, P D; Mulders, G D; Mendigutia, I; Grady, C A; Grankin, K; van Winckel, H; Bacciotti, F; Russell, R W; Lynch, D K; Hammel, H B; Beerman, L C; Day, A N; Huelsman, D M; Werren, C; Henden, A; Grindlay, J

    2014-01-01

    Herbig Ae/Be stars are intermediate-mass pre-main sequence stars surrounded by circumstellar dust disks. Some are observed to produce jets, whose appearance as a sequence of shock fronts (knots) suggests a past episodic outflow variability. This "jet fossil record" can be used to reconstruct the outflow history. We present the first optical to near-infrared (NIR) VLT/X-shooter spectra of the jet from the Herbig Ae star HD 163296. We determine physical conditions in the knots, as well as their kinematic "launch epochs". Knots are formed simultaneously on either side of the disk, with a regular interval of ~16 yr. The velocity dispersion versus jet velocity and the energy input are comparable in both lobes. However, the mass loss rate, velocity, and shock conditions are asymmetric. We find Mjet/Macc ~ 0.01-0.1, consistent with magneto-centrifugal jet launching models. No evidence for dust is found in the high-velocity jet, suggesting it is launched within the sublimation radius (<0.5 au). The jet inclination...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-12-10

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

  16. Photometric and spectroscopic variability of the FUor star V582 Aurigae

    CERN Document Server

    Semkov, E H; Munari, U; Dennefeld, M; Mito, H; Dimitrov, D P; Ibryamov, S; Stoyanov, K A

    2013-01-01

    We carried out BVRI CCD photometric observations in the field of V582 Aur from 2009 August to 2013 February. We acquired high-, medium-, and low-resolution spectroscopy of V582 Aur during this period. To study the pre-outburst variability of the target and construct its historical light curve, we searched for archival observations in photographic plate collections. Both CCD and photographic observations were analyzed using a sequence of 14 stars in the field of V582 Aur calibrated in BVRI. The pre-outburst photographic observations of V582 Aur show low-amplitude light variations typical of T Tauri stars. Archival photographic observations indicate that the increase in brightness began in late 1984 or early 1985 and the star reached the maximum level of brightness at 1986 January. The spectral type of V582 Aur can be defined as G0I with strong P Cyg profiles of H alpha and Na I D lines, which are typical of FU Orionis objects. Our BVRI photometric observations show large amplitude variations V~2.8 mag. during ...

  17. Temporal variability of the wind from the star τ Boötis

    Science.gov (United States)

    Nicholson, B. A.; Vidotto, A. A.; Mengel, M.; Brookshaw, L.; Carter, B.; Petit, P.; Marsden, S. C.; Jeffers, S. V.; Fares, R.; BCool Collaboration

    2016-06-01

    We present new wind models for τ Boötis (τ Boo), a hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely useful target for our goal of monitoring the temporal variability of stellar winds and their exoplanetary impacts. Using spectropolarimetric observations from May 2009 to January 2015, the most extensive information of this type yet available, to reconstruct the stellar magnetic field, we produce multiple 3D magnetohydrodynamic stellar wind models. Our results show that characteristic changes in the large-scale magnetic field as the star undergoes magnetic cycles produce changes in the wind properties, both globally and locally at the position of the orbiting planet. Whilst the mass loss rate of the star varies by only a minimal amount (˜4 per cent), the rates of angular momentum loss and associated spin-down time-scales are seen to vary widely (up to ˜140 per cent), findings consistent with and extending previous research. In addition, we find that temporal variation in the global wind is governed mainly by changes in total magnetic flux rather than changes in wind plasma properties. The magnetic pressure varies with time and location and dominates the stellar wind pressure at the planetary orbit. By assuming a Jovian planetary magnetic field for τ Boo b, we nevertheless conclude that the planetary magnetosphere can remain stable in size for all observed stellar cycle epochs, despite significant changes in the stellar field and the resulting local space weather environment.

  18. Temporal variability of the wind from the star {\\tau} Bo\\"otis

    CERN Document Server

    Nicholson, B A; Mengel, M; Brookshaw, L; Carter, B; Petit, P; Marsden, S C; Jeffers, S V; Fares, R

    2016-01-01

    We present new wind models for {\\tau} Bo\\"otis ({\\tau} Boo), a hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely useful target for our goal of monitoring the temporal variability of stellar winds and their exoplanetary impacts. Using spectropolarimetric observations from May 2009 to January 2015, the most extensive information of this type yet available, to reconstruct the stellar magnetic field, we produce multiple 3D magnetohydrodynamic stellar wind models. Our results show that characteristic changes in the large-scale magnetic field as the star undergoes magnetic cycles produce changes in the wind properties, both globally and locally at the position of the orbiting planet. Whilst the mass loss rate of the star varies by only a minimal amount ($\\sim$ 4 percent), the rates of angular momentum loss and associated spin-down timescales are seen to vary widely (up to $\\sim$ 140 percent), findings consistent with and extending previous research. In addition, we find that temporal variat...

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

    CERN Document Server

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

    2016-01-01

    In this series of papers we have presented the results of a spectroscopic survey of luminous and variable stars in the nearby spirals M31 and M33. In this paper, we present spectroscopy of 132 additional luminous stars, variables, and emission line objects. Most of the stars have emission line spectra, including LBVs and candidate LBVs, Fe II emission line stars and the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. With this large spectroscopic data set including various types of emission line stars, we examine their similarities and differences and propose the following criteria 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 SEDs. 2. Confirmed LBVs do not have the [O I] emission lines in their spectra. Some LBVs have [Fe II] e...

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

    CERN Document Server

    Javadi, Atefeh; Mirtorabi, Mohammad Taghi

    2010-01-01

    We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive dataset was obtained in the K-band with the UIST instrument for the central 4'x 4' (1 square kpc) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18,398 stars in this region; of these, 812 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars, and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the va...

  1. Variable stars in the open cluster NGC 6791 and its surrounding field

    CERN Document Server

    De Marchi, F; Montalto, M; Piotto, G; Desidera, S; Bedin, L R; Claudi, R; Ferro, A Arellano; Bruntt, H; Stetson, P B

    2007-01-01

    Aims: This work presents a high--precision variability survey in the field of the old, super metal-rich open cluster NGC 6791. Methods: The data sample consists of more than 75,000 high-precision CCD time series measurements in the V band obtained mainly at the Canada-France-Hawaii Telescope, with additional data from S. Pedro Martir and Loiano observatories, over a time span of ten nights. The field covers an area of 42x28 arcmin^2. Results: We have discovered 260 new variables and re-determined periods and amplitudes of 70 known variable stars. By means of a photometric evaluation of the membership in NGC 6791, and a preliminary membership based on the proper motions, we give a full description of the variable content of the cluster and surrounding field in the range 16variables with P<4.0 d, while for ones with longer periods the limited time-baseline hampered precise determinations. We categorized the entire sample as follows: 6 pulsating, 3 irregula...

  2. The Gaia spectrophotometric standard stars survey - III. Short-term variability monitoring

    CERN Document Server

    Marinoni, S; Altavilla, G; Bellazzini, M; Galleti, S; Tessicini, G; Valentini, G; Cocozza, G; Ragaini, S; Braga, V; Bragaglia, A; Federici, L; Schuster, W J; Carrasco, J M; Castro, A; Figueras, F; Jordi, C

    2016-01-01

    We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 hour - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725.

  3. The Gaia spectrophotometric standard stars survey - III. Short-term variability monitoring

    Science.gov (United States)

    Marinoni, S.; Pancino, E.; Altavilla, G.; Bellazzini, M.; Galleti, S.; Tessicini, G.; Valentini, G.; Cocozza, G.; Ragaini, S.; Braga, V.; Bragaglia, A.; Federici, L.; Schuster, W. J.; Carrasco, J. M.; Castro, A.; Figueras, F.; Jordi, C.

    2016-11-01

    We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 h - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short-term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725.

  4. 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 firs...

  5. CCD time-series photometry of the globular cluster NGC 6981: Variable star census and physical parameter estimates

    CERN Document Server

    Bramich, D M; Giridhar, Sunetra; Ferro, A Arellano

    2010-01-01

    We present the results from 10 nights of observations of the globular cluster NGC 6981 (M72) in the V, R and I Johnson wavebands. We employed the technique of difference image analysis to perform precision differential photometry on the time-series images, which enabled us to carry out a census of the under-studied variable star population of the cluster. We show that 20 suspected variables in the literature are actually non-variable, and we confirm the variable nature of another 29 variables while refining their ephemerides. We also detect 11 new RR Lyrae variables and 3 new SX Phe variables, bringing the total confirmed variable star count in NGC 6981 to 43. We performed Fourier decomposition of the light curves for a subset of RR Lyrae stars and used the Fourier parameters to estimate the fundamental physical parameters of the stars using relations available in the literature. Mean values of these physical parameters have allowed us to estimate the physical parameters of the parent cluster. We derive a met...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-10

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

  7. The Variable Star One-shot Project, and its little child: Wikimbad

    CERN Document Server

    Foellmi, C; Pritchard, J; Curto, G Lo; Prieto, C Allende; Bruntt, H; Amado, P J; Arentoft, T; Baes, M; Depagne, E; Fernández, M; Ivanov, V D; Koesterke, L; Monaco, L; O'Brien, K; Sarro, L M; Saviane, I; Scharwächter, J; Schmidtobreick, L; Schuetz, O; Seifahrt, A; Selman, F; Stefanon, M; Sterzik, M

    2007-01-01

    The Variable Star One-shot Project (VSOP) aimed at providing to the world-wide stellar community the necessary one-shot spectrum of unstudied variable stars, too often classified as such by an analysis of photometric data only. The VSOP has established an new kind of observational model, where all steps from observations to spectral analysis, are automatized (or are underway to be fully automatized). The project is centralized on a collaborative wiki website. The VSOP operational model is very successful, data is continously flowing and being analyszed, and VSOP is now a worldwide open collaboration of people with very different and complementary skills and expertise. The idea of a central wiki website has been extended by one of us to propose a new service to the whole astronomical community, called Wikimbad. Wikimbad is an open wiki website aimed at collecting, organizing and making publicly available all kind of reduced and published astronomical data. Its strengths and a comparison with the Virtual Observ...

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

    CERN Document Server

    Cusano, Felice; Garofalo, Alessia; Cignoni, Michele; Federici, Luciana; Marconi, Marcella; Musella, Ilaria; Ripepi, Vincenzo; Boutsia, Konstantina; Fumana, Marco; Gallozzi, Stefano; Testa, Vincenzo

    2013-01-01

    We present B,V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.2') of Andromeda's dwarf spheroidal companions, that we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23'x 23' area centered on And XIX and present the deepest color magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V~26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which, however, extends to the blue to significantly populate the classical instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and 3 of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ( = 0.62 d, \\sigma= 0.03 d) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermedia...

  9. Is "Spike" a Reliable Feature in Porb Distribution of AM HER Stars?

    CERN Document Server

    Golovin, Alex; Pavlenko, Elena

    2008-01-01

    Orbital periods in AM Her stars (polars) are synchronized with spin periods of white dwarf by its high magnetic field. Since the last study of Porb distribution of these systems, the number of known objects of such type has more than doubled. This challenged us to compile a new updated catalogue of cataclysmic variables with highly magnetic white dwarfs (polars) and to study their Porb distribution. In this paper we also discus if "spike" is reliable feature in the distribution. ("Spike" is a concentration of polars in the distribution of their orbital periods near Porb = 114 min and was previously discussed by Ritter & Kolb (1992) and Shahbaz & Wood (1996).)

  10. 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.

  11. Improved Variable Star Search in Large Photometric Data Sets -- New Variables in CoRoT Field LRa02 Detected ba BEST II

    CERN Document Server

    Fruth, T; Cabrera, J; Chini, R; Csizmadia, Sz; Eigmüller, P; Erikson, A; Kirste, S; Lemke, R; Murphy, M; Pasternacki, T; Rauer, H; Titz-Weider, R; 10.1088/0004-6256/143/6/140

    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 ...

  12. Characterization of CoRoT target fields with BEST: Identification of periodic variable stars in the IR01 field

    CERN Document Server

    Kabath, P; Erikson, A; Hedelt, P; Rauer, H; Titz, R; Wiese, T; 10.1086/521554

    2009-01-01

    We report on observations of the CoRoT IR01 field with the Berlin Exoplanet Search Telescope (BEST). BEST is a small aperture telescope with a wide field of view (FOV). It is dedicated to search for variable stars within the target fields of the CoRoT space mission to aid in minimizing false-alarm rates and identify potential targets for additional science. CoRoT's observational programm started in February 2007 with the "initial run" field (IR01) observed for about two months. BEST observed this field for 12 nights spread over three months in winter 2006. From the total of 30426 stars observed in the IR01 field 3769 were marked as suspected variable stars and 54 from them showed clear periodicity. From these 19 periodic stars are within the part of the CoRoT FOV covered in our data set.

  13. A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry

    CERN Document Server

    Ferro, A Arellano; Jaimes, R Figuera; Giridhar, Sunetra; Kains, N; Kuppuswamy, K; Jørgensen, U G; Alsubai, K A; Andersen, J M; Bozza, V; Browne, P; Novati, S Calchi; Damerdji, Y; Diehl, C; Dominik, M; Dreizler, S; Elyiv, A; Giannini, E; Harpsøe, K; Hessman, F V; Hinse, T C; Hundertmark, M; Juncher, D; Kerins, E; Korhonen, H; Liebig, C; Mancini, L; Mathiasen, M; Penny, M T; Rabus, M; Rahvar, S; Ricci, D; Scarpetta, G; Skottfelt, J; Snodgrass, C; Southworth, J; Surdej, J; Tregloan-Reed, J; Vilela, C; Wertz, O

    2013-01-01

    We report CCD $V$ and $I$ time-series photometry of the globular cluster NGC 6333 (M9). The technique of difference image analysis has been used, which enables photometric precision better than 0.05 mag for stars brighter than $V \\sim 19.0$ mag, even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RRc stars, three eclipsing binaries, seven long-term variables and one field RRab star behind the cluster. A detailed identification chart and equatorial coordinates are given for all the variable stars in the field of our images of the cluster. Our data together with literature $V$-data obtained in 1994 and 1995 allowed us to refine considerably the periods for all RR Lyrae stars. The nature of the new variables is discussed. We argue that variable V12 is a cluster member and an Anomalous Cepheid. Secular period variations, double mode pulsations and/or the Blazhko-like modulations in some RRc variables are addressed. Through the light curve Fou...

  14. YSOVAR: Mid-IR variability in the star forming region Lynds 1688

    CERN Document Server

    Günther, H M; Covey, K R; Hillenbrand, L A; Plavchan, P; Poppenhaeger, K; Rebull, L M; Stauffer, J R; Wolk, S J; Allen, L; Bayo, A; Gutermuth, R A; Hora, J L; Meng, H Y A; Morales-Calderon, M; Parks, J R; Song, Inseok

    2014-01-01

    The emission from young stellar objects (YSOs) in the mid-IR is dominated by the inner rim of their circumstellar disks. We present an IR-monitoring survey of about 800 objects in the direction of the Lynds 1688 (L1688) star forming region over four visibility windows spanning 1.6 years using the \\emph{Spitzer} space telescope in its warm mission phase. Among all lightcurves, 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 lightcurves 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 years. Non-periodic lightcurves often still show a preferred timescale of variability which is longer for more embedded sources. About half of all sources exhib...

  15. A Deep Catalog of Variable Stars in a 0.66deg^2 Lupus Field

    CERN Document Server

    Weldrake, David T F

    2007-01-01

    We have conducted a wide-field photometric survey in a single 52'x52' field towards the Lupus Galactic Plane in an effort to detect transiting Hot Jupiter planets. The planet Lupus-TR-3b was identified from this work. The dataset also led to the detection of 494 field variables, all of which are new discoveries. This paper presents an overview of the project, along with the total catalog of variables, which comprises 190 eclipsing binaries (of contact, semi-contact and detached configurations), 51 miscellaneous pulsators of various types, 237 long period variables (P>=2d), 11 delta Scuti stars, 4 field RR Lyrae (3 disk and 1 halo) and 1 irregular variable. Our survey provides a complete catalog of W UMa eclipsing binaries in the field to V=18.8, which display a Gaussian period distribution of 0.277+/-0.036d. Several binary systems are likely composed of equal mass M-dwarf components and others display evidence of mass transfer. We find 17 candidate blue stragglers and one binary that has the shortest period k...

  16. Spectral variability of classical T Tauri stars accreting in an unstable regime

    CERN Document Server

    Kurosawa, Ryuichi

    2013-01-01

    Classical T Tauri stars (CTTSs) are variable in different time-scales. One type of variability is possibly connected with the accretion of matter through the Rayleigh-Taylor instability that occurs at the interface between an accretion disc and a stellar magnetosphere. In this regime, matter accretes in a several temporarily formed accretion streams or `tongues' which appear in random locations, and produce stochastic photometric and line variability. We use the results of global three-dimensional magnetohydrodynamic simulations of matter flows in both stable and unstable accretion regimes to calculate time-dependent hydrogen line profiles and study their variability behaviours. In the stable regime, some hydrogen lines (e.g. H-beta, H-gamma, H-delta, Pa-beta and Br-gamma) show a redshifted absorption component only during a fraction of a stellar rotation period, and its occurrence is periodic. However, in the unstable regime, the redshifted absorption component is present rather persistently during a whole s...

  17. Variable Stars in the Large Magellanic Cloud Globular Cluster NGC 2257. I. Results Based on 2007-2008 B, V Photometry

    Science.gov (United States)

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

    2009-11-01

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

  18. An Electronic Version of the Second Volume of the General Catalogue of Variable Stars with Improved Coordinates

    Science.gov (United States)

    Samus', N. N.; Goranskii, V. P.; Durlevich, O. V.; Zharova, A. V.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Williams, D. B.; Hazen, M. L.

    2003-07-01

    We present a new electronic version of the second volume of the fourth edition of the General Catalogue of Variable Stars (GCVS), which contains data on 13 480 variable stars in the constellations Cygnus-Orion (the order of constellations in the Catalogue follows the Latin alphabet). The new version takes into account the Name Lists of Variable Stars from no. 67 to 76 for the same constellations. The main distinctive feature of the new version is that it contains improved equatorial J2000.0 coordinates for 13 446 stars (including those for 5052 stars with an allowance made for proper motions), based on the identifications with positional catalogs using finding charts, as well as on our new measurements. We searched for a number of stars on original plates from the collections of several observatories and using digital sky survey images. The new version also includes a file of remarks to the second and third GCVS volumes. Apart from a complete update of the positional information, we took into account several corrections that were found to be necessary after the publication of the second GCVS volume (1985). We present a list of references to new Internet resources.

  19. The Berlin Exoplanet Search Telescope II. Catalog of Variable Stars. I. Characterization of Three Southern Target Fields

    CERN Document Server

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

    2013-01-01

    A photometric survey of three Southern target fields with BEST II yielded the detection of 2,406 previously unknown variable stars and an additional 617 stars with suspected variability. This study presents a catalog including their coordinates, magnitudes, light curves, ephemerides, amplitudes, and type of variability. In addition, the variability of 17 known objects is confirmed, thus validating the results. The catalog contains a number of known and new variables that are of interest for further astrophysical investigations, in order to, e.g., search for additional bodies in eclipsing binary systems, or to test stellar interior models. Altogether, 209,070 stars were monitored with BEST II during a total of 128 nights in 2009/2010. The overall variability fraction of 1.2-1.5% in these target fields is well comparable to similar ground-based photometric surveys. Within the main magnitude range of $R\\in\\left[11,17\\right]$, we identify 0.67(3)% of all stars to be eclipsing binaries, which indicates a completen...

  20. THE BERLIN EXOPLANET SEARCH TELESCOPE II CATALOG OF VARIABLE STARS. I. CHARACTERIZATION OF THREE SOUTHERN TARGET FIELDS

    Energy Technology Data Exchange (ETDEWEB)

    Fruth, T.; Cabrera, J.; Csizmadia, Sz.; Dreyer, C.; Eigmüller, P.; Erikson, A.; Kabath, P.; Kirste, S.; Pasternacki, T.; Rauer, H.; Titz-Weider, R. [Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt, Rutherfordstr. 2, D-12489 Berlin (Germany); Chini, R.; Lemke, R. [Astronomisches Institut, Ruhr-Universität Bochum, D-44780 Bochum (Germany); Murphy, M., E-mail: thomas.fruth@dlr.de [Departamento de Física, Universidad Católica del Norte, P.O. 1280, Antofagasta (Chile)

    2013-11-01

    A photometric survey of three southern target fields with BEST II yielded the detection of 2406 previously unknown variable stars and an additional 617 stars with suspected variability. This study presents a catalog including their coordinates, magnitudes, light curves, ephemerides, amplitudes, and type of variability. In addition, the variability of 17 known objects is confirmed, thus validating the results. The catalog contains a number of known and new variables that are of interest for further astrophysical investigations, in order to, e.g., search for additional bodies in eclipsing binary systems, or to test stellar interior models. Altogether, 209,070 stars were monitored with BEST II during a total of 128 nights in 2009/2010. The overall variability fraction of 1.2%-1.5% in these target fields is well comparable to similar ground-based photometric surveys. Within the main magnitude range of R in [11, 17], we identify 0.67(3)% of all stars to be eclipsing binaries, which indicates a completeness of about one third for this particular type in comparison to space surveys.