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Sample records for cepheids

  1. Cepheid evolution

    International Nuclear Information System (INIS)

    A review of the phases of stellar evolution relevant to Cepheid variables of both Types I and II is presented. Type I Cepheids arise as a result of normal post-main sequence evolutionary behavior of many stars in the intermediate to massive range of stellar masses. In contrast, Type II Cepheids generally originate from low-mass stars of low metalicity which are undergoing post core helium-burning evolution. Despite great progress in the past two decades, uncertainties still remain in such areas as how to best model convective overshoot, semiconvection, stellar atmospheres, rotation, and binary evolution as well as uncertainties in important physical parameters such as the nuclear reaction rates, opacity, and mass loss rates. The potential effect of these uncertainties on stellar evolution models is discussed. Finally, comparisons between theoretical predictions and observations of Cepheid variables are presented for a number of cases. The results of these comparisons show both areas of agreement and disagreement with the latter result providing incentive for further research

  2. What masses for Cepheids

    International Nuclear Information System (INIS)

    To understand the evolution of giant stars, it is important to pin down the masses for Cepheids. The 7- to 10-day bump Cepheids imply lower than evolutionary mass (60%). Recent theoretical work, though, indicates that for Cepheids with periods of 15 to 16 days, the best understanding of the light curves results from using evolutionary masses

  3. Cepheid Companions and the Masses of Cepheids

    Science.gov (United States)

    Bohm-Vitense, E.; Borutzki, S.; Harris, H.

    The authors have observed in the ultraviolet the hot companions of the Cepheids SV Per, RW Cam, SY Nor and KN Cen. The study of the absolute and relative intensities reveals that all, except the companion for KN Cen are evolved stars which should fit on almost the same mass track as the Cepheid. The authors find however that with generally accepted reddening values the companions of at least SV Per and RW Cam are too faint. Either the Cepheid loops are more luminous than presently calculated or the reddening is larger than presently accepted.

  4. Ultraviolet studies of Cepheids

    Science.gov (United States)

    Boehm-Vitense, Erika

    1992-01-01

    We discuss whether with new evolutionary tracks we still have a problem fitting the Cepheids and their evolved companions on the appropriate evolutionary tracks. We find that with the Bertelli et al. tracks with convective overshoot by one pressure scale height the problem is essentially removed, though somewhat more mixing would give a better fit. By using the results of recent nonlinear hydrodynamic calculations, we find that we also have no problem matching the observed pulsation periods of the Cepheids with those expected from their new evolutionary masses, provided that Cepheids with periods less than 9 days are overtone pulsators. We investigate possible mass loss of Cepheids from UV studies of the companion spectrum of S Mus and from the ultraviolet spectra of the long period Cepheid l Carinae. For S Mus with a period of 9.6 days we derive an upper limit for the mass loss of M less than 10(exp -9) solar mass, if a standard velocity law is assumed for the wind. For l Carinae with a period of 35.5 days we find a probable mass loss of M is approximately 10(exp -5+/-2) solar mass.

  5. The Cepheid Galactic Internet

    CERN Document Server

    Learned, John G; Pakvasa, Sandip; Zee, A

    2008-01-01

    We propose that a sufficiently advanced civilization may employ Cepheid variable stars as beacons to transmit all-call information throughout the galaxy and beyond. One can construct many scenarios wherein it would be desirable for such a civilization of star ticklers to transmit data to anyone else within viewing range. The beauty of employing Cepheids is that these stars can be seen from afar(we monitor them out through the Virgo cluster), and any developing technological society would seem to be likely to closely observe them as distance markers. Records exist of Cepheids for well over one hundred years. We propose that these (and other regularly variable types of stars) be searched for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional signaling.

  6. The Cepheid galactic internet

    Science.gov (United States)

    Learned, John G.; Kudritzki, R.-P.; Pakvasa, Sandip; Zee, A.

    2012-03-01

    We propose that a sufficiently advanced civilisation may employ Cepheid variable stars as beacons to transmit all-call information throughout the galaxy and beyond. They might employ a pulsed neutrino beam to trigger the expansion of a Cepheid at an earlier than normal time, generating a binary signature of normal period or artificially shortened period. One can construct many scenarios wherein it would be desirable for such a civilisation of star ticklers to transmit data to anyone else within viewing range. The beauty of employing Cepheids is that these stars can be seen from afar (we monitor them out through the Virgo cluster), and any developing technological society would seem to be likely to closely observe them as distance markers. Records exist of Cepheids for well over 100 years. We propose that these (and other regularly variable types of stars) be searched for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional signalling.

  7. Subtle flickering in Cepheids

    CERN Document Server

    Evans, N R; Szabados, L; Derekas, A; Kiss, L; Matthews, J; Cameron, C

    2014-01-01

    Fundamental mode classical Cepheids have light curves which repeat accurately enough that we can watch them evolve (change period). The new level of accuracy and quantity of data with the {\\it Kepler} and {\\it MOST} satellites probes this further. An intriguing result was found in the long time-series of Kepler data for V1154 Cyg the one classical Cepheid (fundamental mode, P = 4.9$^d$) in the field, which has short term changes in period ($\\simeq$20 minutes), correlated for $\\simeq$10 cycles (period jitter). To follow this up, we obtained a month long series of observations of the fundamental mode Cepheid RT Aur and the first overtone pulsator SZ Tau. RT Aur shows the traditional strict repetition of the light curve, with the Fourier amplitude ratio $R_1/R_2$ remaining nearly constant. The light curve of SZ Tau, on the other hand, fluctuates in amplitude ratio at the level of approximately $50\\%$. Furthermore prewhitening the RT Aur data with 10 frequencies reduces the Fourier spectrum to noise. For SZ Tau, ...

  8. Binary Cepheids from optical interferometry

    CERN Document Server

    Gallenne, A; Mérand, A; Monnier, J D; Pietrzyński, J Breitfelder G; Gieren, W

    2013-01-01

    Classical Cepheid stars have been considered since more than a century as reliable tools to estimate distances in the universe thanks to their Period-Luminosity (P-L) relationship. Moreover, they are also powerful astrophysical laboratories, providing fundamental clues for studying the pulsation and evolution of intermediate-mass stars. When in binary systems, we can investigate the age and evolution of the Cepheid, estimate the mass and distance, and constrain theoretical models. However, most of the companions are located too close to the Cepheid (1-40 mas) to be spatially resolved with a 10-meter class telescope. The only way to spatially resolve such systems is to use long-baseline interferometry. Recently, we have started a unique and long-term interferometric program that aims at detecting and characterizing physical parameters of the Cepheid companions, with as main objectives the determination of accurate masses and geometric distances.

  9. The chemical composition of Galactic beat Cepheids

    Science.gov (United States)

    Kovtyukh, V.; Lemasle, B.; Chekhonadskikh, F.; Bono, G.; Matsunaga, N.; Yushchenko, A.; Anderson, R. I.; Belik, S.; da Silva, R.; Inno, L.

    2016-08-01

    We determine the metallicity and detailed chemical abundances (α, iron-peak and neutron-capture elements) for the almost complete (18/24) sample of Galactic double mode Cepheids (also called beat Cepheids). Double mode Cepheids are Cepheids that pulsate in two modes simultaneously. We calibrate a new relation between their metallicity and their period ratio P1/P0. This linear relation allows to determine the metallicity of bimodal Cepheids with an accuracy of 0.03 dex in the range of [Fe/H] from +0.2 to -0.5 dex. By extrapolating the relation to Magellanic Clouds beat Cepheids, we provide their metallicity distribution function. Moreover, by using this relation, we also provide the first metallicity estimate for two double-mode F/1O Cepheids located in and beyond the Galactic bulge. Finally, we report the discovery of a super-Lithium rich double mode Cepheid V371 Per which has a Lithium abundance of logA(Li) = 3.54 ± 0.09 dex. Along with V1033 Cyg (which is an ordinary classical Cepheid), it is the second known Cepheid of such type in the Galaxy.

  10. Binarity among Cepheids in the Magellanic Clouds

    OpenAIRE

    Szabados, László; Nehéz, Dóra

    2012-01-01

    Spectroscopic binarity of the Cepheid variable HV914 in the Large Magellanic Cloud is pointed out from the published radial velocity observational data. The list of known binaries among Cepheid type variable stars in the Magellanic Clouds is published in tabular form. The census indicates a serious deficiency of Cepheids with known companions as compared with their Galactic counterparts, whose implications are also discussed. A particular amplitude ratio (A_{V_{rad}}/A_B) of individual Magell...

  11. Cepheid masses for models with enhanced opacities

    International Nuclear Information System (INIS)

    Cepheid models with enhanced opacity are constructed and used to determine pulsation constants, Q0. These are compared to models without an enhanced opacity. Methods of determining Cepheid masses are investigated using the different models and are compared to results obtained by Gieren. The methods to determine the pulsation and Wesselink masses differ significantly, due to the use of a Q0 that varies with mass, radius and luminosity. 14 refs

  12. Anomalous Cepheids in the Sculptor dwarf galaxy

    International Nuclear Information System (INIS)

    The Sculptor dwarf galaxy contains at least three Cepheids (V25, V26, and V119), each with a period near 1 day and B magnitudes about 1.4 mag brighter than those of the Sculptor RR Lyrae stars. Low-resolution spectra of these so-called anomalous Cepheids were obtained. Metal abundances of the Cepheids have been determined by the Delta-S method and are found to be: Fe/H = -1.9 + or - 0.2, -1.8 + or - 0.2, and -2.2 + or - 0.3 for V25, V26, and V119, respectively. These values are consistent with the metal abundances of Sculptor red giants estimated from the color of the giant branch. Pulsational masses have been estimated for V25 and V26, but there is a need for improved photometry of these stars to obtain accurate results. It cannot be unambiguously established whether the Sculptor anomalous Cepheids are evolved single stars, aged about 3 Gyr, or whether they are created by mass transfer in older binary systems. The occurrence of anomalous Cepheids in other systems is discussed. There is some evidence that most anomalous Cepheids in the Small Magellanic Cloud are evolved single stars. 89 references

  13. A search for open cluster Cepheids in the Galactic plane

    CERN Document Server

    Chen, Xiaodian; Deng, Licai

    2014-01-01

    We analyse all potential combinations of Galactic Cepheids and open clusters (OCs) in the most up-to-date catalogues available. Isochrone fitting and proper-motion calcula- tion are applied to all potential OC{Cepheid combinations. Five selection criteria are used to select possible OC Cepheids: (i) the Cepheid of interest must be located within 60 arcmin of the OC's centre; (ii) the Cepheid's proper motion is located within the 1 sigma distribution of that of its host OC; (iii) the Cepheid is located in the instability strip of its postulated host OC; (iv) the Cepheid and OC distance moduli should differ by less than 1 mag; and (v) the Cepheid and OC ages (and, where available, their metal- licities) should be comparable: {\\Delta}log(t yr^-1) < 0.3. Nineteen possible OC Cepheids are found based on our near-infrared (NIR) analysis; eight additional OC{Cepheid associations may be genuine pairs for which we lack NIR data. Six of the Cepheids analysed at NIR wavelengths are new, high-probability OC Cepheids, ...

  14. Using Galactic Cepheids to verify Gaia parallaxes

    CERN Document Server

    Windmark, Fredrik; Hobbs, David

    2011-01-01

    Context. The Gaia satellite will measure highly accurate absolute parallaxes of hundreds of millions of stars by comparing the parallactic displacements in the two fields of view of the optical instrument. The requirements on the stability of the 'basic angle' between the two fields are correspondingly strict, and possible variations (on the microarcsec level) are therefore monitored by an on-board metrology system. Nevertheless, since even very small periodic variations of the basic angle might cause a global offset of the measured parallaxes, it is important to find independent verification methods. Aims. We investigate the potential use of Galactic Cepheids as standard candles for verifying the Gaia parallax zero point. Methods. We simulate the complete population of Galactic Cepheids and their observations by Gaia. Using the simulated data, simultaneous fits are made of the parameters of the period-luminosity relation and a global parallax zero point. Results. The total number of Galactic Cepheids is esti...

  15. Cepheid investigations using the Kepler space telescope

    CERN Document Server

    Szabó, R; Ngeow, C -C; Smolec, R; Derekas, A; Moskalik, P; Nuspl, J; Lehmann, H; Fűrész, G; Molenda-Zakowicz, J; Bryson, S T; Henden, A A; Kurtz, D W; Stello, D; Nemec, J M; Benkő, J M; Berdnikov, L; Bruntt, H; Evans, N R; Gorynya, N A; Pastukhova, E N; Simcoe, R J; Grindlay, J E; Los, E J; Doane, A; Laycock, S G; Mink, D J; Champine, G; Sliski, A; Handler, G; Kiss, L L; Kolláth, Z; Kovács, J; Christensen-Dalsgaard, J; Kjeldsen, H; Allen, C; Thompson, S E; Van Cleve, J

    2011-01-01

    We report results of initial work done on selected candidate Cepheids to be observed with the Kepler space telescope. Prior to the launch 40 candidates were selected from previous surveys and databases. The analysis of the first 322 days of Kepler photometry, and recent ground-based follow-up multicolour photometry and spectroscopy allowed us to confirm that one of these stars, V1154 Cyg (KIC 7548061), is indeed a 4.9-d Cepheid. Using the phase lag method we show that this star pulsates in the fundamental mode. New radial velocity data are consistent with previous measurements, suggesting that a long-period binary component is unlikely. No evidence is seen in the ultra-precise, nearly uninterrupted Kepler photometry for nonradial or stochastically excited modes at the micromagnitude level. The other candidates are not Cepheids but an interesting mix of possible spotted stars, eclipsing systems and flare stars.

  16. The period-age relation for cepheids

    International Nuclear Information System (INIS)

    The list of 119 cepheid-members of 55 clusters and associations of the Magellanic Clouds, the Galaxy, and M31 is given. The period-age relation is found from the data on 64 cepheids in 29 clusters for which the age determinations are available, the ages of extragalactic clusters were determined mainly from their integral colours. The U-B colours are found to be of much better age parameters than the B-V ones. The composite period-age relation agrees well with the theoretical one. The observed dispersion of the period-age relation leads to an estimate of the age dispersion about 1x107 years in the associations. Some peculiarities of the cepheids with the shortest periods amongst others in the same clusters are probably explained if they are overtone pulsators. The period-age relation may be used for an investigation of the recent history of star formation in the galaxies. This relation allows to determine the age gradient across the spiral arm in M31 which is in agreement with the density wave theory predictions. The distribution of cepheids in our Galaxy and neighbouring galaxies is consistent with the conception of star formation lasting for some dozen million years in cells with a dimension of some hundreds of parsecs

  17. A Global Physical Model for Cepheids

    CERN Document Server

    Pejcha, Ondrej

    2011-01-01

    We perform a global fit to ~5,000 radial velocity and ~177,000 magnitude measurements in 29 photometric bands covering 0.3 to 8.0 microns distributed among 287 Galactic, LMC, and SMC Cepheids with P > 10 days. We assume that the Cepheid light curves and radial velocities are fully characterized by distance, reddening, and time-dependent radius and temperature variations. We construct phase curves of radius and temperature for periods between 10 and 100 days, which yield light curve templates for all our photometric bands and can be easily generalized to any additional band. With only 4 to 6 parameters per Cepheid, depending on the existence of velocity data and the amount of freedom in the distance, the models have typical rms light and velocity curve residuals of 0.05 mag and 3.5 km/s. The model derives the mean Cepheid spectral energy distribution and its derivative with respect to temperature, which deviate from a black body in agreement with metal-line and molecular opacity effects. We determine a mean re...

  18. Kinematics of classical Cepheids in the Nuclear Stellar Disk

    CERN Document Server

    Matsunaga, N; Yamamoto, R; Kobayashi, N; Inno, L; Genovali, K; Bono, G; Baba, J; Fujii, M S; Kondo, S; Ikeda, Y; Hamano, S; Nishiyama, S; Nagata, T; Aoki, W; Tsujimoto, T

    2014-01-01

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic Center, three of which were reported in 2011, the other reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the Nuclear Stellar Disk, a group of stars and interstellar matter occupying a region of 200 pc around the Center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the Nuclear Stellar Disk like younger stars and stellar clusters therein.

  19. Cepheid Variables in the Maser-Host Galaxy NGC 4258

    CERN Document Server

    Hoffmann, Samantha L

    2015-01-01

    We present results of a ground-based survey for Cepheid variables in NGC 4258. This galaxy plays a key role in the Extragalactic Distance Scale due to its very precise and accurate distance determination via VLBI observations of water masers. We imaged two fields within this galaxy using the Gemini North telescope and GMOS, obtaining 16 epochs of data in the SDSS gri bands over 4 years. We carried out PSF photometry and detected 94 Cepheids with periods between 7 and 127 days, as well as an additional 215 variables which may be Cepheids or Population II pulsators. We used the Cepheid sample to test the absolute calibration of theoretical gri Period-Luminosity relations and found good agreement with the maser distance to this galaxy. The expected data products from the Large Synoptic Survey Telescope (LSST) should enable Cepheid searches out to at least 10 Mpc.

  20. Anomalous Cepheid period-luminosity relationships

    International Nuclear Information System (INIS)

    The P-L relationship for anomalous Cepheids (ACs) splits into two well-defined lines in the log P - M(B) plane. One line corresponds to pulsation in the fundamental mode, and the other corresponds to the first-overtone. If these P-L relationships are universal, then they can be used to estimate distances to nearby dwarf galaxies. Knowledge of pulsation modes of the ACs in Draco suggests a mass range of 1.04 to 1.7 solar mass

  1. New NIR light-curve templates for classical Cepheids

    CERN Document Server

    Inno, L; Romaniello, M; Bono, G; Monson, A; Ferraro, I; Iannicola, G; Persson, E; Buonanno, R; Freedman, W; Gieren, W; Groenewegen, M A T; Ita, Y; Laney, C D; Lemasle, B; Madore, B F; Nagayama, T; Nakada, Y; Nonino, M; Pietrzynski, G; Primas, F; Scowcroft, V; Soszynski, I; Tanabe, T; Udalski, A

    2014-01-01

    We present new near-infrared (NIR) light-curve templates for fundamental (FU, JHK) and first overtone (FO, J) Cepheids. The new templates together with PL and PW relations provide Cepheid distances from single-epoch observations with a precision only limited by the intrinsic accuracy of the method adopted. The templates rely on a very large set of Galactic and Magellanic Clouds (MCs) Cepheids (FU,~600; FO,~200) with well sampled NIR (IRSF data) and optical (V,I; OGLE data) light curves. To properly trace the change in the shape of the light curve as a function of period, we split the sample of calibrating Cepheids into 10 different period bins. The templates for the first time cover FO Cepheids and the FU short-period Cepheids (P<5 days). Moreover, the zero-point phase is anchored to the phase of the mean magnitude along the rising branch. The new approach has several advantages in sampling the light curve of bump Cepheids when compared with the phase of maximum light. We also provide new estimates of the ...

  2. KIC2569073, A second Cepheid in the Kepler FOV

    Directory of Open Access Journals (Sweden)

    Drury Jason A.

    2015-01-01

    Full Text Available One particularly interesting new variable discovered via Kepler’s 200x200 pixel superstamp images is KIC2569073. With a period of 14.66 days and 0.04mag variability it is only the second Cepheid in the Kepler field, or a rotationally modulated variable. We discuss its classification as a Type II W Virginis Class Cepheid, and present the cycle-to-cycle period variations of this star, as well as the first direct observations of granulation noise within a Cepheid.

  3. The Cepheid in the eclipsing binary system OGLE-LMC-CEP1812 is a stellar merger

    Science.gov (United States)

    Neilson, Hilding; Ignace, Richard

    2014-06-01

    Classical Cepheids and eclipsing binary systems are powerful probes for measuring stellar fundamental parameters and constraining stellar astrophysics. A Cepheid in an eclipsing binary system is even more powerful, constraining stellar physics, the distance scale and the Cepheid mass discrepancy. However, these systems are rare, only three have been discovered. One of these, OGLE-LMC-CEP1812, presents a new mystery: where the Cepheid component appears to be younger than its red giant companion. In this work, we present stellar evolution models and show that the Cepheid is actually product of a stellar merger during main sequence evolution that causes the Cepheid to be a rejuvenated star. This result raises new questions into the evolution of Cepheids and their connections to smaller-mass anomalous Cepheids.

  4. The application of a correlation analysis to the study of the cepheid distribution in the LMC

    Science.gov (United States)

    Karimova, G. I.

    1989-09-01

    The correlation function was used to study the cepheid distribution in the LMC. This distribution is shown to be nonuniform. A method for determining the characteristic size of groups of cepheids is proposed. This size is 200 pk. The size of the region in the LMC characterized by a nonuniform cepheid distribution is at least 2-3 kpk.

  5. The VMC Survey. VI. First results for Classical Cepheids

    CERN Document Server

    Ripepi, V; Marconi, M; Clementini, G; Cioni, M R; Marquette, J B; Girardi, L; Rubele, S; Groenewegen, M A T; de Grijs, R; Gibson, B K; Oliveira, J M; van Loon, J Th

    2012-01-01

    The VISTA Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted by the system formed by the two Magellanic Clouds (MCs) and the "bridge" connecting them. In this paper we present the first results for Classical Cepheids, from the VMC observations of two fields in the Large Magellanic Cloud (LMC). The VMC Ks-band light curves of the Cepheids are well sampled (12-epochs) and of excellent precision. We were able to measure for the first time the Ks magnitude of the faintest Classical Cepheids in the LMC (Ks\\sim17.5 mag), which are mostly pulsating in the First Overtone (FO) mode, and to obtain FO Period-Luminosity (PL), Period-Wesenheit (PW), and Period-Luminosity-Color (PLC) relations, spanning a whole period range from 0.25 to 6 days. Saturation limits our Ks measurements of the Fundamental mode (F) Cepheids to periods shorter than 15-20 days. Therefore, we have complemented our sample with literature data for brighter F Cepheids. ...

  6. Period-Luminosity Relations Derived From the OGLE-III Fundamental Mode Cepheids II: The Small Magellanic Cloud Cepheids

    CERN Document Server

    Ngeow, Chow-Choong; Bhardwaj, Anupam; Singh, Harinder P

    2015-01-01

    In this paper we present multi-band period-luminosity (P-L) relations for fundamental mode Cepheids in the SMC. The optical VI-band mean magnitudes for these SMC Cepheids were taken from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III) catalog. We also matched the OGLE-III SMC Cepheids to 2MASS and SAGE-SMC catalog to derive mean magnitudes in the JHK-bands and the four {\\it Spitzer} IRAC bands, respectively. All photometry was corrected for extinction by adopting the Zaritsky's extinction map. Cepheids with periods smaller than $\\sim2.5$ days were removed from the sample. In addition to the extinction corrected P-L relations in nine filters from optical to infrared, we also derived the extinction-free Wesenheit function for these Cepheids. We tested the nonlinearity of these SMC P-L relations (except the $8.0\\mu\\mathrm{m}$-band P-L relation) at 10 days: none of the P-L relations show statistically significant evidence of nonlinearity. When compared to the P-L relations in the LMC, t...

  7. The Secret Lives of Cepheids: Evolutionary Changes and Pulsation-Induced Shock Heating in the Prototype Classical Cepheid {\\delta} Cep

    CERN Document Server

    Engle, Scott G; Harper, Graham M; Neilson, Hilding R; Evans, Nancy Remage

    2014-01-01

    Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well-understood. In this, the first of several planned papers on program Cepheids, we report the current results for delta Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light curve morphology and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov 2000 returns a small period change of dP/dt ~ -0.1006 +/- 0.0002 sec yr^-1. There is also evidence for a gradual light amplitude increase of ~0.011-mag (V-band) and ~0.012-mag (B-band) per decade over the last ~50 years. In addition, HST-COS UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, delta Cep is found to be a sof...

  8. Cepheids at high angular resolution: circumstellar envelope and pulsation

    Science.gov (United States)

    Gallenne, Alexandre

    2011-12-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out a statistical study of the speckle noise and inspect a possible asymmetry. Secondly, I analysed VISIR data to study the spectral energy distribution of a sample of Cepheids. These diffraction-limited images enabled me to carry out an accurate photometry in the N band and to detect an IR excess linked to the presence of a circumstellar component. On the other hand, applying a Fourier analysis I showed that some components are resolved. I then explored the K' band with the recombination instrument FLUOR for some bright Cepheids. Thanks to new set of data of Y Oph, I improved the study of its circumstellar envelope, using a ring-like model for the CSE. For two other Cepheids, U Vul and S Sge, I applied the interferometric Baade-Wesselink method in order to estimate their distance.

  9. The strange evolution of the Large Magellanic Cloud Cepheid OGLE-LMC-CEP1812

    CERN Document Server

    Neilson, Hilding R; Langer, Norbert; Ignace, Richard

    2015-01-01

    Classical Cepheids are key probes of both stellar astrophysics and cosmology as standard candles and pulsating variable stars. It is important to understand Cepheids in unprecedented detail in preparation for upcoming GAIA, JWST and extremely-large telescope observations. Cepheid eclipsing binary stars are ideal tools for achieving this goal, however there are currently only three known systems. One of those systems, OGLE-LMC-CEP1812, raises new questions about the evolution of classical Cepheids because of an apparent age discrepancy between the Cepheid and its red giant companion. We show that the Cepheid component is actually the product of a stellar merger of two main sequence stars that has since evolved across the Hertzsprung gap of the HR diagram. This post-merger product appears younger than the companion, hence the apparent age discrepancy is resolved. We discuss this idea and consequences for understanding Cepheid evolution.

  10. The strange evolution of the Large Magellanic Cloud Cepheid OGLE-LMC-CEP1812

    Science.gov (United States)

    Neilson, Hilding R.; Izzard, Robert G.; Langer, Norbert; Ignace, Richard

    2015-09-01

    Classical Cepheids are key probes of both stellar astrophysics and cosmology as standard candles and pulsating variable stars. It is important to understand Cepheids in unprecedented detail in preparation for upcoming Gaia, James Webb Space Telescope (JWST) and extremely-large telescope observations. Cepheid eclipsing binary stars are ideal tools for achieving this goal, however there are currently only three known systems. One of those systems, OGLE-LMC-CEP1812, raises new questions about the evolution of classical Cepheids because of an apparent age discrepancy between the Cepheid and its red giant companion. We show that the Cepheid component is actually the product of a stellar merger of two main sequence stars that has since evolved across the Hertzsprung gap of the HR diagram. This post-merger product appears younger than the companion, hence the apparent age discrepancy is resolved. We discuss this idea and consequences for understanding Cepheid evolution.

  11. The Secret Lives of Cepheids: Evolution, Mass-Loss, and Ultraviolet Emission of the Long-period Classical Cepheid

    Science.gov (United States)

    Neilson, Hilding R.; Engle, Scott G.; Guinan, Edward F.; Bisol, Alexandra C.; Butterworth, Neil

    2016-06-01

    The classical Cepheid l Carinae is an essential calibrator of the Cepheid Leavitt Law as a rare long-period Galactic Cepheid. Understanding the properties of this star will also constrain the physics and evolution of massive (M ≥ 8 M ⊙) Cepheids. The challenge, however, is precisely measuring the star's pulsation period and its rate of period change. The former is important for calibrating the Leavitt Law and the latter for stellar evolution modeling. In this work, we combine previous time-series observations spanning more than a century with new observations to remeasure the pulsation period and compute the rate of period change. We compare our new rate of period change with stellar evolution models to measure the properties of l Car, but find models and observations are, at best, marginally consistent. The results imply that l Car does not have significantly enhanced mass-loss rates like that measured for δ Cephei. We find that the mass of l Car is about 8–10 M ⊙. We present Hubble Space Telescope Cosmic Origins Spectrograph observations that also differ from measurements for δ Cep and β Dor. These measurements further add to the challenge of understanding the physics of Cepheids, but do hint at the possible relation between enhanced mass-loss and ultraviolet emission, perhaps both due to the strength of shocks propagating in the atmospheres of Cepheids. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13019. This work is also based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), associated with program #060374.

  12. The Effective Temperatures, Radii and Masses of Dwarf Cepheids

    Science.gov (United States)

    Kim, Chulhee

    1996-02-01

    Using the flux values determined with the infrared flux method (IRFM) developed by Blackwell and Lynas-Gray (1993), we derived the empirical relationship between flux (F v ) and (V — K) colour appropriate to Dwarf Cepheids. For three Dwarf Cepheids CY Aqr, YZ Boo and SZ Lyn where both VK photometry and radial velocities were available from the literature, effective temperatures were determined using the intrinsic Strömgren indices, model atmosphere grids for (V — K) and the relation between temperature and (V — K) colour. Then, by applying the infrared surface brightness method, radii and distances and hence masses and absolute magnitudes were estimated with effective temperatures determined by three different methods. It was found that the average mass of these variables is about 0.5 solar mass and this result supports the hypothesis that Dwarf Cepheids are pre-white dwarf objects. It was also confirmed that the temperatures determined with the IRFM are most successful in the application of the surface brightness method to the radius estimation of Dwarf Cepheids.

  13. The reliability of Cepheid reddenings based on BVIC photometry

    Science.gov (United States)

    Laney, C. David; Caldwell, John A. R.

    2007-05-01

    Externally determined values of E(B - V) (Espacered) for 40 Galactic Cepheids are compared to reddenings determined using B - V and V - IC colour indices and the method of Dean, Warren & Cousins (EBVIC), updated to allow for metallicity corrections. With three stars omitted on the grounds of uncertainty in their space reddenings, we find that The two scales agree well in scale and zero-point, and there is no significant trend with period. Given the non-zero errors in the Cepheid space reddenings, the estimated error in BVIC Cepheid reddenings is no more than 0.02. The above results are not significantly changed whether one corrects the reddenings for metallicity using older Bell models, or using more recent models by Sandage, Bell & Tripicco. Using the SBT models to correct the reddenings of Cloud Cepheids for metallicity gives slightly smaller reddenings at a given metal deficiency, yielding `new' median reddenings of 0.056 (Small Magellanic Cloud) and 0.076 (Large Magellanic Cloud) if we assume the same metal deficiencies as Caldwell and Coulson. With metal deficiencies of [M/H] = -0.7 and -0.25, the median reddenings are 0.040 and 0.058.

  14. CoRoT space photometry of seven Cepheids

    CERN Document Server

    Poretti, Ennio; Rainer, Monica; Baglin, Annie; Benko, Jozsef; Debosscher, Jonas; Weiss, Werner W

    2015-01-01

    A few Galactic classical Cepheids were observed in the programmes of space missions as Coriolis, MOST and Kepler. An appealing opportunity was to detect additional nonradial modes, thus opening the possibility to perform asteroseismic studies and making the pulsational content of Galactic Cepheids more similar to that of Magellanic Clouds ones. However, only hints of cycle-to-cycle variations were found, without any strict periodicity. In this context the potential of the CoRoT exoplanetary data base was not fully exploited despite the wide area covered on the Galactic plane. Therefore, we investigated all the candidate Cepheids pointed out by the automatic classification of the CoRoT curves. At the end we could identify seven bona-fide Cepheids. The light curves were investigated to remove some instrumental effects. The frequency analysis was particularly delicate since these small effects can be enhanced by the large amplitude, resulting in the presence of significant, but spurious, peaks in the power spect...

  15. THE PULSATION MODE AND DISTANCE OF THE CEPHEID FF AQUILAE

    International Nuclear Information System (INIS)

    The determination of pulsation mode and distance for field Cepheids is a complicated problem best resolved by a luminosity estimate. For illustration a technique based on spectroscopic luminosity discrimination is applied to the 4.47 day s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variable yield values of (MV ) = –3.40 ± 0.02 s.e. (±0.04 s.d.), average effective temperature Teff = 6195 ± 24 K, and intrinsic color ((B) – (V))0 = +0.506 ± 0.007, corresponding to a reddening of EB–V = 0.25 ± 0.01, or EB–V(B0) = 0.26 ± 0.01. The skewed light curve, intrinsic color, and luminosity of FF Aql are consistent with fundamental mode pulsation for a small-amplitude classical Cepheid on the blue side of the instability strip, not a sinusoidal pulsator. A distance of 413 ± 14 pc is estimated from the Cepheid's angular diameter in conjunction with a mean radius of (R) = 39.0 ± 0.7 R☉ inferred from its luminosity and effective temperature. The dust extinction toward FF Aql is described by a ratio of total-to-selective extinction of RV = AV /E(B – V) = 3.16 ± 0.34 according to the star's apparent distance modulus

  16. The period distribution of Cepheids: a test of stellar evolution

    Directory of Open Access Journals (Sweden)

    Groenewegen M.A.T.

    2015-01-01

    Full Text Available The period distributions of classical Cepheids in the Small and Large Magellanic Cloud are quite different. Using the TRILEGAL population synthesis code and a theoretical instability strip the ultimate aim is to understand these differences quantitatively. First results are presented for one area in the LMC using VMC NIR data.

  17. The Scale of Reddening for Classical Cepheid Variables

    CERN Document Server

    Turner, David G

    2016-01-01

    Field reddenings are summarized for 68 Cepheids from published studies and updated results presented here. The compilation forms the basis for a comparison with other published reddening scales of Cepheids, including those established from reddening-independent indices, photometry on the Lick six-color system, Str\\"{o}mgren system, Walraven system, Washington system, Cape $BVI$ system, DDO system, and Geneva system, IRSB studies, and Cepheid spectroscopy, both old and new. Reddenings tied to period-color relations are the least reliable, as expected, while photometric color excesses vary in precision, their accuracy depending on the methodology and calibration sample. The tests provide insights into the accuracy and precision of published Cepheid reddening scales, and lead to a new system of standardized reddenings comprising a sample of 198 variables with an average uncertainty of $\\pm0.028$ in E$_{B-V}$, the precision being less than $\\pm0.01$ for many. The collected color excesses are used to map the dispe...

  18. The Secret Lives of Cepheids: Evolution, Mass Loss, and Ultraviolet Emission of the Long-Period Classical Cepheid $l$ Carinae

    CERN Document Server

    Neilson, Hilding R; Guinan, Edward F; Bisol, Alexandra C; Butterworth, Neil

    2016-01-01

    The classical Cepheid $l$ Carinae is an essential calibrator of the Cepheid Leavitt Law as a rare long-period Galactic Cepheid. Understanding the properties of this star will also constrain the physics and evolution of massive ($M \\ge 8$ $M_\\odot$) Cepheids. The challenge, however, is precisely measuring the star's pulsation period and its rate of period change. The former is important for calibrating the Leavitt Law and the latter for stellar evolution modeling. In this work, we combine previous time-series observations spanning more than a century with new observations to remeasure the pulsation period and compute the rate of period change. We compare our new rate of period change with stellar evolution models to measure the properties of $l$ Car, but find models and observations are, at best, marginally consistent. The results imply that $l$ Car does not have significantly enhanced mass-loss rates like that measured for $\\delta$ Cephei. We find that the mass of $l$ Car is about 8 - 10 $M_\\odot$. We present...

  19. The secret lives of Cepheids: evolutionary changes and pulsation-induced shock heating in the prototype classical Cepheid δ Cep

    Energy Technology Data Exchange (ETDEWEB)

    Engle, Scott G.; Guinan, Edward F. [Department of Astrophysics and Planetary Science, Villanova University, Villanova, PA 19085 (United States); Harper, Graham M. [School of Physics, Trinity College Dublin, College Green, Dublin 2 (Ireland); Neilson, Hilding R. [Department of Physics and Astronomy, East Tennessee State University, Box 70652, Johnson City, TN 37614 (United States); Evans, Nancy Remage, E-mail: scott.engle@villanova.edu [Smithsonian Astrophysical Observatory, MS 4, 60 Garden Street, Cambridge, MA 02138 (United States)

    2014-10-10

    Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well understood. In this, the first of several planned papers on program Cepheids, we report the current results for δ Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light-curve morphology, and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov et al. returns a small period change of dP/dt ≈–0.1006 ± 0.0002 s yr{sup -1}. There is also evidence for a gradual light amplitude increase of ∼0.011 mag (V band) and ∼0.012 mag (B band) per decade over the last ∼50 years. In addition, Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, δ Cep is found to be a soft X-ray source (L {sub X} (0.3-2 keV) ≈4.5-13 × 10{sup 28} erg s{sup -1}) with peak flux at kT = 0.6-0.9 keV. The X-ray activity is found to vary, possibly in phase with the stellar pulsations. From 2010-2013, nine observations of δ Cep were carried out with HST-COS. The UV emissions are also variable and well phased with the stellar pulsations. Maximum UV line emissions occur near, or slightly before, maximum optical light, varying by as much as 20 times. This variability shows that pulsation-induced shock heating plays a significant role in Cepheid atmospheres, possibly in addition to a quiescent, magnetic heating. The results of this study show Cepheid atmospheres to be rather complex and dynamic.

  20. The secret lives of Cepheids: evolutionary changes and pulsation-induced shock heating in the prototype classical Cepheid δ Cep

    International Nuclear Information System (INIS)

    Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well understood. In this, the first of several planned papers on program Cepheids, we report the current results for δ Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light-curve morphology, and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov et al. returns a small period change of dP/dt ≈–0.1006 ± 0.0002 s yr-1. There is also evidence for a gradual light amplitude increase of ∼0.011 mag (V band) and ∼0.012 mag (B band) per decade over the last ∼50 years. In addition, Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, δ Cep is found to be a soft X-ray source (L X (0.3-2 keV) ≈4.5-13 × 1028 erg s-1) with peak flux at kT = 0.6-0.9 keV. The X-ray activity is found to vary, possibly in phase with the stellar pulsations. From 2010-2013, nine observations of δ Cep were carried out with HST-COS. The UV emissions are also variable and well phased with the stellar pulsations. Maximum UV line emissions occur near, or slightly before, maximum optical light, varying by as much as 20 times. This variability shows that pulsation-induced shock heating plays a significant role in Cepheid atmospheres, possibly in addition to a quiescent, magnetic heating. The results of this study show Cepheid atmospheres to be rather complex and dynamic.

  1. Cepheids in Open Clusters: An 8-D All-sky Census

    CERN Document Server

    Anderson, Richard I; Mowlavi, Nami

    2012-01-01

    Cepheids in open clusters (cluster Cepheids: CCs) are of great importance as zero- point calibrators of the Galactic Cepheid period-luminosity relationship (PLR). We perform an 8-dimensional all-sky census that aims to identify new bona- fide CCs and provide a ranking of membership confidence for known CC candidates through membership probabilities. The probabilities are computed for combinations of known Galactic open clusters and classical Cepheid candidates, based on spatial, kine- matic, and population-specific membership constraints. Data employed in this analysis are taken largely from published literature and supplemented by a year-round observ- ing program on both hemispheres dedicated to determining systemic radial velocities of Cepheids. In total, we find 13 bona-fide CCs, 3 of which are identified for the first time, including an overtone-Cepheid member in NGC 129. Inconclusive cases are discussed in detail, some of which have been previously mentioned in the literature. Our results are inconsisten...

  2. Classical Cepheid pulsation models --- VI. The Hertzsprung progression

    Science.gov (United States)

    Bono, G.; Marconi, M.; Stellingwerf, R. F.

    2000-08-01

    We present the results of an extensive theoretical investigation on the pulsation behavior of Bump Cepheids. We constructed several sequences of full amplitude, nonlinear, convective models by adopting a chemical composition typical of Large Magellanic Cloud (LMC) Cepheids (Y=0.25, Z=0.008) and stellar masses ranging from M/M⊙ =6.55 to 7.45. We find that theoretical light and velocity curves reproduce the HP, and indeed close to the blue edge the bump is located along the descending branch, toward longer periods it crosses at first the luminosity/velocity maximum and then it appears along the rising branch. In particular, we find that the predicted period at the HP center is PHP = 11.24∓0.46 d and that such a value is in very good agreement with the empirical value estimated by adopting the Fourier parameters of LMC Cepheid light curves i.e. PHP = 11.2 ∓ 0.8 d (Welch et al. 1997). Moreover, light and velocity amplitudes present a "double-peaked" distribution which is in good qualitative agreement with observational evidence on Bump Cepheids. It turns out that both the skewness and the acuteness typically show a well-defined minimum at the HP center and the periods range from PHP = 10.73 ∓ 0.97 d to PHP = 11.29 ∓ 0.53 d which are in good agreement with empirical estimates. We also find that the models at the HP center are located within the resonance region but not on the 2:1 resonance line (P2/P0 = 0.5), and indeed the P2/P0 ratios roughly range from 0.51 (cool models) to 0.52 (hot models). Interestingly enough, the predicted Bump Cepheid masses, based on a Mass-Luminosity (ML) relation which neglects the convective core overshooting, are in good agreement with the empirical masses of Galactic Cepheids estimated by adopting the Baade-Wesselink method (Gieren 1989). As a matter of fact, the observed mass at the HP center -P ≍ 11.2 d- is 6.9 ∓ 0.9 M⊙, while the predicted mass is 7.0 ∓ 0.45 M⊙. Even by accounting for the metallicity difference

  3. Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc

    OpenAIRE

    Lemasle, B.; Francois, P.; Piersimoni, A.; Pedicelli, S.; Bono, G.; Laney, C. D.; Primas, F.; Romaniello, M.

    2008-01-01

    Context: Classical Cepheids can be adopted to trace the chemical evolution of the Galactic disk since their distances can be estimated with very high accuracy. Aims: Homogeneous iron abundance measurements for 33 Galactic Cepheids located in the outer disk together with accurate distance determinations based on near-infrared photometry are adopted to constrain the Galactic iron gradient beyond 10 kpc. Methods: Iron abundances were determined using high resolution Cepheid spectra collected wit...

  4. Study of the cepheid distribution in the LMC by the Meads method

    International Nuclear Information System (INIS)

    The distribution of the cepheids in the LMC was studied by the Meads analysis. All cepheids and the group of stars with lgP=0.4-0.69 have the scale of non-uniformity about 700-1400 pk. The cepheids in the regions of the bar have the scale of non-uniformity ≅200pk. This scale was also obtained by the correlation analysis

  5. The angular diameter and distance of the Cepheid Zeta Geminorum

    CERN Document Server

    Kervella, P; Perrin, G; Schöller, M; Traub, W A; Lacasse, M D

    2001-01-01

    Cepheids are the primary distance indicators for extragalactic astronomy and therefore are of very high astrophysical interest. Unfortunately, they are rare stars, situated very far from Earth.Though they are supergiants, their typical angular diameter is only a few milliarcseconds, making them very challenging targets even for long-baseline interferometers. We report observations that were obtained in the K prime band (2-2.3 microns), on the Cepheid Zeta Geminorum with the FLUOR beam combiner, installed at the IOTA interferometer. The mean uniform disk angular diameter was measured to be 1.64 +0.14 -0.16 mas. Pulsational variations are not detected at a significant statistical level, but future observations with longer baselines should allow a much better estimation of their amplitude. The distance to Zeta Gem is evaluated using Baade-Wesselink diameter determinations, giving a distance of 502 +/- 88 pc.

  6. Double-Overtone Cepheids in the Large Magellanic Cloud

    CERN Document Server

    Dziembowski, W A

    2009-01-01

    One of the most interesting results from the OGLE-III study of the LMC Cepheids is the large number of objects that pulsate simultaneously in the first and second overtone (denoted 1O/2O). Double-mode Cepheids yield important constraint on stellar evolution models. We show that great majority of the LMC 1O/2O Cepheids have masses M=3.0+/-0.5 Msun. According to current stellar evolution calculations, these masses are lower than needed for the blue loop in the helium burning phase to reach the instability strip. On the other hand, we found most of these stars significantly overluminous if they are crossing the instability before helium ignition. A possible solution of this discrepancy is to allow for a large overshooting from the convective core in the main sequence phase. We also discuss origin of double-mode pulsation. At the short period range we find two types of resonances that are conducive to this form of pulsation. However, at longer periods, it has a different (non-resonant) origin.

  7. Cepheids at high angular resolution: circumstellar envelope and pulsation

    CERN Document Server

    Gallenne, Alexandre

    2011-01-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out ...

  8. Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements

    CERN Document Server

    Breitfelder, Joanne; Kervella, Pierre; Gallenne, Alexandre; Szabados, Laszlo; Anderson, Richard I; Bouquin, Jean-Baptiste Le

    2016-01-01

    The distance to pulsating stars is classically estimated using the parallax-of-pulsation (PoP) method, which combines spectroscopic radial velocity measurements and angular diameter estimates to derive the distance of the star. An important application of this method is the determination of Cepheid distances, in view of the calibration of their distance scale. However, the conversion of radial to pulsational velocities in the PoP method relies on a poorly calibrated parameter, the projection factor (p-factor). We aim to measure empirically the value of the p-factors of a homogeneous sample of nine Galactic Cepheids for which trigonometric parallaxes were measured with the Hubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, a robust implementation of the PoP method that combines photometry, interferometry, and radial velocity measurements in a global modeling of the pulsation. We obtained new interferometric angular diameters using the PIONIER instrument at the Very Large Telescope Interfe...

  9. Population I Cepheids and understanding star formation history of the Small Magellanic Cloud

    International Nuclear Information System (INIS)

    In this paper, we study the age and spatial distributions of Cepheids in the Small Magellanic Cloud (SMC) as a function of their ages using data from the OGLE III photometric catalogue. A period - age relation derived for Classical Cepheids in the Large Magellanic Cloud (LMC) has been used to find the ages of Cepheids. The age distribution of the SMC Classical Cepheids is found to have a peak at log(Age) = 8.40 ± 0.10 which suggests that a major star formation event might have occurred in the SMC about 250 ± 50 Myr ago. It is believed that this star forming burst had been triggered by close interactions of the SMC with the LMC and/or the Milky Way. A comparison of the observed spatial distributions of the Cepheids and open star clusters has also been carried out to study the star formation scenario in the SMC. (paper)

  10. CEPHEID VARIABLE STARS IN THE PEGASUS DWARF IRREGULAR GALAXY: CONSTRAINTS ON THE STAR FORMATION HISTORY

    International Nuclear Information System (INIS)

    Observations of the resolved stars obtained over a period of 11 years in the Local Group dwarf irregular galaxy Pegasus have been used to search for Cepheid variable stars. Images were obtained in 55 epochs in the V band and in 24 epochs in the I band. We have identified 26 Cepheids and have obtained their light curves and periods. On the basis of their position in the period-luminosity (PL) diagram, we have classified them as 18 fundamental modes and eight first overtone Cepheids. Two PL relations for Cepheids have been used to derive the distance, resulting in 1.07 ± 0.05 Mpc. We present the VARFINDER code which finds the variable stars and their predicted periods in a given synthetic color-magnitude diagram computed with IAC-star and we propose the use of the Cepheid population as a constraint of the star formation history of Pegasus.

  11. Comparison of multi-band period-luminosity relations for classical Cepheids in the Magellanic Clouds

    Science.gov (United States)

    Ngeow, Chow-Choong; Kanbur, Shashi M.

    2016-07-01

    The period-luminosity (PL) relation for classical fundamental mode Cepheids (hereafter Cepheids) is an important astrophysical tool in distance scale applications. Because of this, we initiated a program to derive multi-band PL relations with Cepheids in the Large and Small Magellanic Cloud (hereafter LMC and SMC, respectively), as there are ∼⃒ 103 Cepheids found in these two nearby galaxies. When compared the slopes of the multi-band PL relations for Cepheids in the LMC and SMC, we found that these PL slopes agree with each others except in the V and J band. We also found an excellent agreement of the PL slopes in Wesenheit function, hence we calibrated the Period-Wesenheit (PW) relation by combining the data from both Clouds, together with an accurate LMC distance based on measurement from late-type eclipsing binaries. Our calibrated Wesenheit function is MW = — 3.314 log(P) — 2.601.

  12. Empirical Period-Color and Amplitude-Color Relations for Classical Cepheids and RR Lyrae Variables

    CERN Document Server

    Bhardwaj, Anupam; Singh, Harinder P; Ngeow, Chow-Choong

    2014-01-01

    We analyze Galactic, Large Magellanic Cloud and Small Magellanic Cloud Cepheids and RR Lyrae variables in terms of period-color (PC) and amplitude-color (AC) diagrams at the phases of maximum and minimum light. We compiled Galactic Cepheids $V$- and $I$-band data from the literature. We make use of optical bands light curve data from OGLE-III survey for Cepheids and RR Lyrae variables in the Magellanic Clouds. We apply the $F$-statistical test to check the significance of any variation in the slope of PC and AC relations for Cepheid variables. The PC relation at maximum light for Galactic Cepheids with periods longer than about 7 days is shallow and the corresponding AC relation is flat for the entire period range. For the fundamental mode Cepheids in the Magellanic Clouds, we find significant breaks in the PC and AC relations at both maximum and minimum light for periods around 10 days. The PC relation at maximum light for the Magellanic Clouds is flat for Cepheids with periods greater than 10 days. First ov...

  13. Resolved Companions of Cepheids: Testing the Candidates with X-Ray Observations

    Science.gov (United States)

    Evans, Nancy Remage; Pillitteri, Ignazio; Wolk, Scott; Karovska, Margarita; Tingle, Evan; Guinan, Edward; Engle, Scott; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.

    2016-04-01

    We have made XMM-Newton observations of 14 Galactic Cepheids that have candidate resolved (≥5″) companion stars based on our earlier HST Wide Field Camera 3 (WFC3) imaging survey. Main-sequence stars that are young enough to be physical companions of Cepheids are expected to be strong X-ray producers in contrast to field stars. XMM-Newton exposures were set to detect essentially all companions hotter than spectral type M0 (corresponding to 0.5 M⊙). The large majority of our candidate companions were not detected in X-rays, and hence are not confirmed as young companions. One resolved candidate (S Nor #4) was unambiguously detected, but the Cepheid is a member of a populous cluster. For this reason, it is likely that S Nor #4 is a cluster member rather than a gravitationally bound companion. Two further Cepheids (S Mus and R Cru) have X-ray emission that might be produced by either the Cepheid or the candidate resolved companion. A subsequent Chandra observation of S Mus shows that the X-rays are at the location of the Cepheid/spectroscopic binary. R Cru and also V659 Cen (also X-ray bright) have possible companions closer than 5″ (the limit for this study) which are the likely sources of X-rays. One final X-ray detection (V473 Lyr) has no known optical companion, so the prime suspect is the Cepheid itself. It is a unique Cepheid with a variable amplitude. The 14 stars that we observed with XMM constitute 36% of the 39 Cepheids found to have candidate companions in our HST/WFC3 optical survey. No young probable binary companions were found with separations of ≥5″ or 4000 au. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).

  14. Period-Luminosity Relations For Magellanic Clouds Cepheids Based on OGLE-III Data: A Comparison

    OpenAIRE

    Ngeow, Chow-Choong

    2011-01-01

    The period-luminosity (P-L) relation for Cepheid variables is important in modern astrophysics. In this work, we present the multi-band P-L relations derived from the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) Cepheids, based on the latest release of OGLE-III catalogs. In addition to the V I band mean magnitudes adopted from OGLE-III catalogs, we also cross-matched the LMC and SMC Cepheids to the 2MASS point source catalogs and publicly available Spitzer catalogs from SAGE ...

  15. THE DISTANCE MEASUREMENT OF NGC 1313 WITH CEPHEIDS

    Energy Technology Data Exchange (ETDEWEB)

    Qing, Gao; Wang, Wei; Liu, Ji-Feng [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Yoachim, Peter [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2015-01-20

    We present the detection of Cepheids in the barred spiral galaxy NGC 1313, using the Wide Field and Planetary Camera 2 on the Hubble Space Telescope. Twenty B(F450W) and V(F555W) epochs of observations spanning over three weeks were obtained, on which the profile-fitting photometry of all stars in the monitored field was performed using the package HSTphot. A sample of 26 variable stars have been identified to be Cepheids, with periods between 3 and 14 days. Based on the derived period-luminosity relations in B- and V-bands, we obtain an extinction-corrected distance modulus of μ{sub NGC} {sub 1313} = 28.32 ± 0.08 (random) ± 0.06 (systematic), employing the Large Magellanic Cloud as the distance zero point calibrator. The above moduli correspond to a distance of 4.61 ± 0.17 (random) ±0.13 (systematic) Mpc, consistent with previous measurements reported in the literature within uncertainties. In addition, the reddening to NGC 1313 is found to be small.

  16. The Distance Measurement of NGC 1313 With Cepheids

    CERN Document Server

    Gao, Qing; Liu, Ji-Feng; Yoachim, Peter

    2016-01-01

    We present the detection of Cepheids in the barred spiral galaxy NGC 1313, using the Wide Field and Planetary Camera 2 on the Hubble Space Telescpoe. Twenty B (F450W) and V (F555W) epochs of observations spanning over three weeks were obtained, on which the profile-fitting photometry of all stars in the monitored field was performed using the package HSTphot. A sample of 26 variable stars have been identified to be Cepheids, with periods between 3 and 14 days. Based on the derived period-luminosity relations in B and V bands, we obtain an extinction-corrected distance modulus of mu = 28.32 +- 0.08 (random) +- 0.06 (systematic), employing the Large Magellanic Cloud as the distance zero point calibrator. The above moduli correspond to a distance of 4.61 +- 0.17 (random) +- 0.13 (systematic) Mpc, consistent with previous measurements reported in the literature with uncertainties. In addition, the reddening to NGC 1313 is found to be small.

  17. The Secret Lives of Cepheids: A Multi-Wavelength Study of the Atmospheres and Real-Time Evolution of Classical Cepheids

    CERN Document Server

    Engle, Scott G

    2015-01-01

    The primary goal of this study is to observe how complex the behaviors of Cepheids can be, and to show how the continued monitoring of Cepheids at multiple wavelengths can begin to reveal their "secret lives." We aim to achieve this through optical photometry, UV spectroscopy and X-ray imaging. Through Villanova's guaranteed access to ground-based telescopes, we have secured well-covered light curves as regularly as possible. Amplitudes and times of max brightness were obtained and compared to previous literature results. At UV wavelengths, we have secured hi-res spectra of 2 nearby Cepheids - delta Cep and beta Dor - with HST-COS. Also, we have obtained X-ray images of 5 Cepheids with XMM-Newton and the Chandra X-ray Observatory, and further observations with both satellites have been proposed for (XMM) and approved (Chandra). Optical photometry has shown that 8 of the 10 observed Cepheids have amplitude variability, or hints thereof, and all 10 show period variability (recent, long-term or possibly periodic...

  18. X-Ray, UV and Optical Observations of Classical Cepheids: New Insights into Cepheid Evolution, and the Heating and Dynamics of Their Atmospheres

    CERN Document Server

    Engle, Scott G; 10.5140/JASS.2012.29.2.181

    2012-01-01

    To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic origins spectrograph (COS) FUV-UV spectra of the bright, nearby Cepheids Polaris, {\\delta} Cep and {\\beta} Dor. Previous studies made with the international ultraviolet explorer (IUE) showed a limited number of UV emission lines in Cepheids. The well-known problem presented by scattered light contamination in IUE spectra for bright stars, along with the excellent sensitivity & resolution combination offered by HST/COS, motivated this study, and the spectra obtained were much more rich and complex than we had ever anticipated. Numerous emission lines, indicating 10^4 K up to ~3 x 10^5 K plasmas, have been observed, showing Cepheids to have complex, dynamic outer atmospheres that also vary with the photospheric pulsation period. The FUV line emissions peak in the phase ra...

  19. Period-Luminosity Relations For Magellanic Clouds Cepheids Based on OGLE-III Data: A Comparison

    CERN Document Server

    Ngeow, Chow-Choong

    2011-01-01

    The period-luminosity (P-L) relation for Cepheid variables is important in modern astrophysics. In this work, we present the multi-band P-L relations derived from the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) Cepheids, based on the latest release of OGLE-III catalogs. In addition to the V I band mean magnitudes adopted from OGLE-III catalogs, we also cross-matched the LMC and SMC Cepheids to the 2MASS point source catalogs and publicly available Spitzer catalogs from SAGE program. Mean magnitudes for these Cepheids were corrected for extinction using available extinction maps. When comparing the P-L slopes, we found that the P-L slopes in these two galaxies are consistent with each others within ~2.5sigma level.

  20. Hubble Space Telescope: Snapshot Survey for Resolved Companions of Galactic Cepheids

    CERN Document Server

    Evans, Nancy Remage; Schaefer, Gail H; Mason, Brian D; Tingle, Evan; Karovska, Margarita; Pillitteri, Ignazio

    2016-01-01

    We have conducted an imaging survey with the Hubble Space Telescope Wide Field Camera~3 (WFC3) of 70 Galactic Cepheids, typically within 1~kpc, with the aim of finding resolved physical companions. The WFC3 field typically covers the 0.1 pc area where companions are expected. In this paper, we identify 39 Cepheids having candidate companions, based on their positions in color--magnitude diagrams, and having separations $\\geq$5$"$ from the Cepheids. We use follow-up observations of 14 of these candidates with XMM-Newton, and of one of them with ROSAT, to separate X-ray-active young stars (probable physical companions) from field stars (chance alignments). Our preliminary estimate, based on the optical and X-ray observations, is that only 3\\% of the Cepheids in the sample have wide companions. Our survey easily detects resolved main-sequence companions as faint as spectral type K\

  1. MACHO observations of Type II cepheids and RV Tauri Stars in the LMC

    Energy Technology Data Exchange (ETDEWEB)

    Alcock, C.; Pollard, K.A.; Alisman, R.A. [and others

    1996-07-01

    We report the of the existence of RV Tauri stars in the Large Magellanic Cloud (LMC). This class of variable star has hitherto been unidentified in the Magellanic Clouds. In light and color curve behavior the RV Tauri stars appear to be an extension of the Type II Cepheids to longer periods. A single period-luminosity-color relationship is seen to describe both the Type II Cepheids and the RV Tauri stars in the LMC.

  2. The PL calibration for Milky Way Cepheids and its implications for the distance scale

    CERN Document Server

    Turner, David G

    2009-01-01

    The rationale behind recent calibrations of the Cepheid PL relation using the Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent conclusions regarding a possible change in slope of the PL relation for short-period and long-period Cepheids are tied to a pathological distribution of HST calibrators within the instability strip. A recalibration of the period-luminosity relation is obtained using Galactic Cepheids in open clusters and groups, the resulting relationship, described by log L/L_sun = 2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter expected from color spread within the instability strip. The relationship is confirmed by Cepheids with HST parallaxes, although without the need for Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos parallaxes, albeit with concerns about the cited precisions of the latter. A Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for Galactic Cepheids is tested successfully using Cep...

  3. OGLE-ing the Magellanic System: Three-Dimensional Structure of the Clouds and the Bridge Using Classical Cepheids

    Science.gov (United States)

    Jacyszyn-Dobrzeniecka, A. M.; Skowron, D. M.; Mróz, P.; Skowron, J.; Soszyński, I.; Udalski, A.; Pietrukowicz, P.; Kozłowski, S.; Wyrzykowski, Ł.; Poleski, R.; Pawlak, M.; Szymański, M. K.; Ulaczyk, K.

    2016-06-01

    We analyzed a sample of 9418 fundamental-mode and first-overtone classical Cepheids from the OGLE-IV Collection of Classical Cepheids. The distance to each Cepheid was calculated using the period-luminosity relation for the Wesenheit magnitude, fitted to our data. The classical Cepheids in the LMC are situated mainly in the bar and in the northern arm. The eastern part of the LMC is closer to us and the plane fit to the whole LMC sample yields the inclination i=24.°2 ±0.°7 and position angle P.A.=151.°4±1.°7. We redefined the LMC bar by extending it in the western direction and found no offset from the plane of the LMC contrary to previous studies. On the other hand, we found that the northern arm is offset from a plane by about -0.5 kpc, which was not observed before. The age distribution of the LMC Cepheids shows one maximum at about 100 Myr. We demonstrate that the SMC has a non-planar structure and can be described as an extended ellipsoid. We identified two large ellipsoidal off-axis structures in the SMC. The northern one is located closer to us and is younger, while the south-western is farther and older. The age distribution of the SMC Cepheids is bimodal with one maximum at 110 Myr, and another one at 220 Myr. Younger stars are located in the closer part of this galaxy while older ones are more distant. We classified nine Cepheids from our sample as Magellanic Bridge objects. These Cepheids show a large spread in three-dimensions although five of them form a connection between the Clouds. The closest one is closer than any of the LMC Cepheids, while the farthest one - farther than any SMC Cepheid. All but one Cepheids in the Magellanic Bridge are younger than 300 Myr. The oldest one can be associated with the SMC Wing.

  4. CEPHEID CALIBRATIONS OF MODERN TYPE Ia SUPERNOVAE: IMPLICATIONS FOR THE HUBBLE CONSTANT

    International Nuclear Information System (INIS)

    This is the first of two papers reporting measurements from a program to determine the Hubble constant to ∼5% precision from a refurbished distance ladder. We present new observations of 110 Cepheid variables in the host galaxies of two recent Type Ia supernovae (SNe Ia), NGC 1309 and NGC 3021, using the Advanced Camera for Surveys on the Hubble Space Telescope (HST). We also present new observations of the hosts previously observed with HST whose SNe Ia provide the most precise luminosity calibrations: SN 1994ae in NGC 3370, SN 1998aq in NGC 3982, SN 1990N in NGC 4639, and SN 1981B in NGC 4536, as well as the maser host, NGC 4258. Increasing the interval between observations enabled the discovery of new, longer-period Cepheids, including 57 with P>60 days, which extend these period-luminosity (P-L) relations. We present 93 measurements of the metallicity parameter, 12 + log[O/H], measured from H II regions in the vicinity of the Cepheids and show these are consistent with solar metallicity. We find the slope of the seven dereddened P-L relations to be consistent with that of the Large Magellanic Cloud Cepheids and with parallax measurements of Galactic Cepheids, and we address the implications for the Hubble constant. We also present multi-band light curves of SN 2002fk (in NGC 1309) and SN 1995al (in NGC 3021) which may be used to calibrate their luminosities. In the second paper, we present observations of the Cepheids in the H band obtained with the Near-Infrared Camera and Multi-Object Spectrometer on HST, further mitigating systematic errors along the distance ladder resulting from dust and chemical variations. The quality and homogeneity of these SN and Cepheid data provide the basis for a more precise determination of the Hubble constant.

  5. The Cepheid distance to the maser-host galaxy NGC 4258: Studying systematics with the Large Binocular Telescope

    CERN Document Server

    Fausnaugh, M M; Gerke, J R; Macri, L M; Riess, A G; Stanek, K Z

    2014-01-01

    We identify and phase a sample of 81 Cepheids in the maser-host galaxy NGC 4258 using the Large Binocular Telescope (LBT), and obtain calibrated mean magnitudes in up to 4 filters for a subset of 43 Cepheids using archival HST data. We employ 3 models to study the systematic effects of extinction, the assumed extinction law, and metallicity on the Cepheid distance to NGC 4258. We find a correction to the Cepheid colors consistent with a grayer extinction law in NGC 4258 compared to the Milky Way ($R_V =4.9$), although we believe this is indicative of other systematic effects. If we combine our Cepheid sample with previously known Cepheids, we find a significant metallicity adjustment to the distance modulus of $\\gamma_1 = -0.60 \\pm 0.21$ mag/dex, for the Zaritsky et al. (1994) metallicity scale, as well as a weak trend of Cepheid colors with metallicity. Conclusions about the absolute effect of metallicity on Cepheid mean magnitudes appear to be limited by the available data on the metallicity gradient in NGC...

  6. The Secret XUV Lives of Cepheids: FUV/X-ray Observations of Polaris and beta Dor

    CERN Document Server

    Engle, Scott G; DePasquale, Joseph; Evans, Nancy

    2009-01-01

    We report on the surprising recent discovery of strong FUV emissions in two bright, nearby Classical Cepheids from analyses of FUSE archival observations and one of our own approved observations just prior to the failure of the satellite. Polaris and beta Dor are currently the only two Cepheids to have been observed with FUSE, and beta Dor is the only one to have multiple spectra. Both Cepheids show strong C III (977A, 1176A) and O VI (1032A, 1038A) emissions, indicative of 50,000-500,000 K plasma, well above the photospheric temperatures of the stars. More remarkably, beta Dor displays variability in the FUV emission strengths which appears to be correlated to its 9.84-d pulsation period. This phenomenon has never before been observed in Cepheids. The FUV studies are presented along with our recent Chandra/XMM X-ray observations of Polaris and beta Dor, in which X-ray detections were found for both stars (as well as for the prototype Classical Cepheid, delta Cep). Further X-ray observations have been propose...

  7. Period-Luminosity Relations for Cepheid Variables: From Mid-Infrared to Multi-Phase

    CERN Document Server

    Ngeow, Chow-Choong; Bellinger, Earl P; Marconi, Marcella; Musella, Ilaria; Cignoni, Michele; Lin, Ya-Hong

    2012-01-01

    This paper discusses two aspects of current research on the Cepheid period-luminosity (P-L) relation: the derivation of mid-infrared (MIR) P-L relations and the investigation of multi-phase P-L relations. The MIR P-L relations for Cepheids are important in the James Webb Space Telescope era for the distance scale issue, as the relations have potential to derive the Hubble constant within ~ 2% accuracy - a critical constraint in precision cosmology. Consequently, we have derived the MIR P-L relations for Cepheids in the Large and Small Magellanic Clouds, using archival data from Spitzer Space Telescope. We also compared currently empirical P-L relations for Cepheids in the Magellanic Clouds to the synthetic MIR P-L relations derived from pulsational models. For the study of multi-phase P-L relations, we present convincing evidence that the Cepheid P-L relations in the Magellanic Clouds are highly dynamic quantities that vary significantly when considered as a function of pulsational phase. We found that there ...

  8. Resolved Companions of Cepheids: Testing the Candidates with X-Ray Observations

    CERN Document Server

    Evans, Nancy Remage; Wolk, Scott; Karovska, Margarita; Tingle, Evan; Guinan, Edward; Engle, Scott; Bond, Howard E; Schaefer, Gail H; Mason, Brian D

    2016-01-01

    We have made {\\it XMM-Newton\\/} observations of 14 Galactic Cepheids that have candidate resolved ($\\geq$5$\\arcsec$) companion stars based on our earlier {\\it HST\\/} WFC3 imaging survey. Main-sequence stars that are young enough to be physical companions of Cepheids are expected to be strong X-ray producers in contrast to field stars. {\\it XMM-Newton\\/} exposures were set to detect essentially all companions hotter than spectral type M0 (corresponding to 0.5 $ M_\\odot$.) The large majority of our candidate companions were not detected in X-rays, and hence are not confirmed as young companions. One resolved candidate (S~Nor \\#4) was unambiguously detected, but the Cepheid is a member of a populous cluster. For this reason, it is likely that S~Nor \\#4 is a cluster member rather than a gravitationally bound companion. Two further Cepheids (S~Mus and R~Cru) have X-ray emission that might be produced by either the Cepheid or the candidate resolved companion. A subsequent {\\it Chandra} observation of S Mus shows th...

  9. Non-linear modelling of beat Cepheids: Resonant and non-resonant models

    CERN Document Server

    Smolec, R

    2010-01-01

    The phenomenon of double-periodic Cepheid pulsation is still poorly understood. Recently we rediscussed the problem of modelling the double-periodic pulsation with non-linear hydrocodes. We showed that the published non-resonant double-mode models are incorrect, because they exclude the negative buoyancy effects. Aims. We continue our efforts to verify whether the Kuhfuss one-equation convection model with negative buoyancy included can reproduce the double-periodic Cepheid pulsation. Methods. Using the direct time integration hydrocode, which implements the Kuhfuss convection model, we search for stable double-periodic Cepheid models. We search for models pulsating in both fundamental and first overtone modes (F+1O), as well as in the two lowest order overtones (1O+2O). In the latter case, we focus on reproducing double-overtone Cepheids of the Large Magellanic Cloud (LMC). Results. We have found full amplitude non-linear beat Cepheid models of both types, F+1O and 1O+2O. In the case of F+1O models, the beat...

  10. Multiphase Spectroscopic Observations of the Long-Period Cepheids l Carinae

    Science.gov (United States)

    Usenko, I. A.; Kravtsov, V. V.; Kovtyukh, V. V.; Berdnikov, L. N.; Knyazev, A. Yu.; Chini, R.; Fokin, A. B.

    Thirty three spectra (one spectrum for the each of 33 observational nights) have been performed to coverall pulsational period of the 35.5-days Cepheid l Car. Due to these data we have obtained for the first time the detailed curves of effective temperature, gravity and turbulent velocity. Curves of gravity and turbulent velocity show complicated changes, connected probably with dynamics of extensive Cepheid's atmosphere. The mean atmosphere parameters of l Car are: Teff =4984±15K; log g = 1.13; Vt =6.67kms-1. Having a solar metallicity[Fe/H]=+0.02dex, this Cepheid demonstrate sudden results for the "key" elements abundances of yellow supergiants evolution, - all they are close to the solar ones. In this case l Car resembles to SV Vul, - Cepheid with 45-days pulsational period and nearly like spectral type. It is possible that l Car is an object crossing the Cepheids instability strip for the first time. The content of other elements is close to solar one too.

  11. Updated 24 $\\mu\\mathrm{m}$ Period-Luminosity Relation Derived from Galactic Cepheids

    CERN Document Server

    Ngeow, Chow-Choong; Bhardwaj, Anupam; Kanbur, Shashi M; Singh, Harinder P

    2015-01-01

    In this work, we updated the catalog of Galactic Cepheids with $24\\mu\\mathrm{m}$ photometry by cross-matching the positions of known Galactic Cepheids to the recently released MIPSGAL point source catalog. We have added 36 new sources featuring MIPSGAL photometry in our analysis, thus increasing the existing sample to 65. Six different sources of compiled Cepheid distances were used to establish a $24\\mu\\mathrm{m}$ period-luminosity (P-L) relation. Our recommended $24\\mu\\mathrm{m}$ P-L relation is $M_{24\\mu\\mathrm{m}}=-3.18(\\pm0.10)\\log P - 2.46(\\pm0.10)$, with an estimated intrinsic dispersion of 0.20 mag, and is derived from 58 Cepheids exhibiting distances based on a calibrated Wesenheit function. The slopes of the P-L relations were steepest when tied solely to the 10 Cepheids exhibiting trigonometric parallaxes from the Hubble Space Telescope and Hipparcos. Statistical tests suggest that these P-L relations are significantly different from those associated with other methods of distance determination, an...

  12. VizieR Online Data Catalog: BVI photometry of OGLE LMC Cepheids (Udalski+, 1999)

    Science.gov (United States)

    Udalski, A.; Soszynski, I.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Wozniak, P.; Zebrun, K.

    2000-01-01

    We present the Catalog of Cepheids from the LMC. The Catalog contains 1333 objects detected in the 4.5 square degree area of central parts of the LMC. About 3.4*105 BVI measurements of these stars were collected during the OGLE-II microlensing survey. The Catalog data include period, BVI photometry, astrometry, and R21, phi21 parameters of the Fourier decomposition of I-band light curve. The vast majority of objects from the Catalog are the classical Cepheids pulsating in the fundamental or first overtone mode. The remaining objects include Population II Cepheids and red giants with pulsation-like light curves. Tests of completeness performed in overlapping parts of adjacent fields indicate that completeness of the Catalog is very high: >96%. Statistics and distributions of basic parameters of Cepheids are also presented. Finally, we show the light curves of three eclipsing systems containing Cepheid detected among objects of the Catalog. All presented data, including individual BVI observations are available from the OGLE Internet archive at URL: ftp://sirius.astrouw.edu.pl/ogle/ogle2/var_stars/lmc/cep/catalog/ (3 data files).

  13. The ACS LCID Project. VIII. The short-period Cepheids of Leo A

    CERN Document Server

    Bernard, Edouard J; Gallart, Carme; Fiorentino, Giuliana; Cassisi, Santi; Aparicio, Antonio; Cole, Andrew A; Drozdovsky, Igor; Hidalgo, Sebastian L; Skillman, Evan D; Stetson, Peter B; Tolstoy, Eline

    2013-01-01

    We present the results of a new search for variable stars in the Local Group dwarf galaxy Leo A, based on deep photometry from the Advanced Camera for Surveys onboard the Hubble Space Telescope. We detected 166 bona fide variables in our field, of which about 60 percent are new discoveries, and 33 candidate variables. Of the confirmed variables, we found 156 Cepheids, but only 10 RR Lyrae stars despite nearly 100 percent completeness at the magnitude of the horizontal branch. The RR Lyrae stars include 7 fundamental and 3 first-overtone pulsators, with mean periods of 0.636 and 0.366 day, respectively. From their position on the period-luminosity (PL) diagram and light-curve morphology, we classify 91, 58, and 4 Cepheids as fundamental, first-overtone, and second-overtone mode Classical Cepheids (CC), respectively, and two as population II Cepheids. However, due to the low metallicity of Leo A, about 90 percent of the detected Cepheids have periods shorter than 1.5 days. Comparison with theoretical models ind...

  14. Updated 24 μm Period-Luminosity Relation Derived from Galactic Cepheids

    Science.gov (United States)

    Ngeow, Chow-Choong; Sarkar, Saurjya; Bhardwaj, Anupam; Kanbur, Shashi M.; Singh, Harinder P.

    2015-11-01

    In this work, we updated the catalog of Galactic Cepheids with 24 μm photometry by cross-matching the positions of known Galactic Cepheids to the recently released MIPSGAL point source catalog. We have added 36 new sources featuring MIPSGAL photometry in our analysis, thus increasing the existing sample to 65. Six different sources of compiled Cepheid distances were used to establish a 24 μm period-luminosity (P-L) relation. Our recommended 24 μm P-L relation is {M}24μ {{m}}=-3.18(+/- 0.10){log}P-2.46(+/- 0.10), with an estimated intrinsic dispersion of 0.20 mag, and is derived from 58 Cepheids exhibiting distances based on a calibrated Wesenheit function. The slopes of the P-L relations were steepest when tied solely to the 10 Cepheids exhibiting trigonometric parallaxes from the Hubble Space Telescope and Hipparcos. Statistical tests suggest that these P-L relations are significantly different from those associated with other methods of distance determination, and simulations indicate that difference may arise from the small sample size.

  15. A lack of classical Cepheids in the inner part of the Galactic disk

    CERN Document Server

    Matsunaga, Noriyuki; Bono, Giuseppe; Kobayashi, Naoto; Inno, Laura; Nagayama, Takahiro; Nishiyama, Shogo; Matsuoka, Yoshiki; Nagata, Tetsuya

    2016-01-01

    Recent large-scale infrared surveys have been revealing stellar populations in the inner Galaxy seen through strong interstellar extinction in the disk. In particular, classical Cepheids with their period-luminosity and period-age relations are useful tracers of Galactic structure and evolution. Interesting groups of Cepheids reported recently include four Cepheids in the Nuclear Stellar Disk (NSD), about 200 pc around the Galactic Centre, found by Matsunaga et al. and those spread across the inner part of the disk reported by Dekany and collaborators. We here report our discovery of nearly thirty classical Cepheids towards the bulge region, some of which are common with Dekany et al., and discuss the large impact of the reddening correction on distance estimates for these objects. Assuming that the four Cepheids in the NSD are located at the distance of the Galactic Centre and that the near-infrared extinction law, i.e. wavelength dependency of the interstellar extinction, is not systematically different bet...

  16. The Distribution of the Elements in the Galactic Disk II. Azimuthal and Radial Variation in Abundances from Cepheids

    CERN Document Server

    Luck, R E; Kovtyukh, V V; Gieren, W; Graczyk, D

    2011-01-01

    This paper reports on the spectroscopic investigation of 101 Cepheids in the Carina region. These Cepheids extend previous samples by about 35% in number and increase the amount of the galactic disk coverage especially in the direction of l \\approx 270{\\deg}. The new Cepheids do not add much information to the radial gradient, but provide a substantial increase in azimuthal coverage. We find no azimuthal dependence in abundance over an 80{\\deg} angle from the galactic center in an annulus of 1 kpc depth centered on the Sun. A simple linear fit to the Cepheid data yields a gradient d[Fe/H]/dRG = -0.055 \\pm 0.003 dex/kpc which is somewhat shallower than found from our previous, smaller Cepheid sample.

  17. Panchromatic Hubble Andromeda Treasury. XIV. The Period-Age Relationship of Cepheid Variables in M31 Star Clusters

    CERN Document Server

    Senchyna, Peter; Dalcanton, Julianne J; Beerman, Lori C; Fouesneau, Morgan; Dolphin, Andrew; Williams, Benjamin F; Rosenfield, Philip; Larsen, Søren S

    2015-01-01

    We present a sample of 11 M31 Cepheids in stellar clusters, derived from the overlap of the Panchromatic Hubble Andromeda Treasury (PHAT) cluster catalog and the Pan-STARRS1 (PS1) disk Cepheid catalog. After identifying the PS1 Cepheids in the HST catalog, we calibrate the PS1 mean magnitudes using the higher resolution HST photometry, revealing up to 1 magnitude offsets due to crowding effects in the ground-based catalog. We measure ages of the clusters by performing single stellar population fits to their color-magnitude diagrams (CMDs) excluding their Cepheids. From these cluster age measurements, we derive an empirical period-age relation which agrees well with the existing literature values. By confirming this relation for M31 Cepheids, we justify its application in high-precision pointwise age estimation across M31.

  18. Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements

    Science.gov (United States)

    Breitfelder, J.; Mérand, A.; Kervella, P.; Gallenne, A.; Szabados, L.; Anderson, R. I.; Le Bouquin, J.-B.

    2016-03-01

    Context. The distance to pulsating stars is classically estimated using the parallax-of-pulsation (PoP) method, which combines spectroscopic radial velocity (RV) measurements and angular diameter (AD) estimates to derive the distance of the star. A particularly important application of this method is the determination of Cepheid distances in view of the calibration of their distance scale. However, the conversion of radial to pulsational velocities in the PoP method relies on a poorly calibrated parameter, the projection factor (p-factor). Aims: We aim to measure empirically the value of the p-factors of a homogeneous sample of nine bright Galactic Cepheids for which trigonometric parallaxes were measured with the Hubble Space Telescope (HST) Fine Guidance Sensor. Methods: We use the SPIPS algorithm, a robust implementation of the PoP method that combines photometry, interferometry, and radial velocity measurements in a global modeling of the pulsation of the star. We obtained new interferometric angular diameter measurements using the PIONIER instrument at the Very Large Telescope Interferometer (VLTI), completed by data from the literature. Using the known distance as an input, we derive the value of the p-factor of the nine stars of our sample and study its dependence with the pulsation period. Results: We find the following p-factors: p = 1.20 ± 0.12 for RT Aur, p = 1.48 ± 0.18 for T Vul, p = 1.14 ± 0.10 for FF Aql, p = 1.31 ± 0.19 for Y Sgr, p = 1.39 ± 0.09 for X Sgr, p = 1.35 ± 0.13 for W Sgr, p = 1.36 ± 0.08 for β Dor, p = 1.41 ± 0.10 for ζ Gem, and p = 1.23 ± 0.12 for ℓ Car. Conclusions: The values of the p-factors that we obtain are consistently close to p = 1.324 ± 0.024. We observe some dispersion around this average value, but the observed distribution is statistically consistent with a constant value of the p-factor as a function of the pulsation period (χ2 = 0.669). The error budget of our determination of the p-factor values is

  19. Emission lines in the long period Cepheid l Carinae

    Science.gov (United States)

    Boehm-Vitense, Erika; Love, Stanley G.

    1991-01-01

    For the Cepheid (l) Carinae with a pulsation period of 35.5 days we have studied the emission line fluxes as a function of pulsational phase in order to find out whether we see chromosphere and transition layer emission or whether we see emission due to an outward moving shock. All emission lines show a steep increase in flux shortly before maximum light suggestive of a shock moving through the surface layers. The large ratio of the C IV to C II line fluxes shows that these are not transition layer lines. During maximum light the large ratio of the C IV to C II line fluxes also suggests that we see emission from a shock with velocities greater than 100 km/sec such that C IV emission can be excited. With such velocities mass outflow appears possible. The variations seen in the Mg II line profiles show that there is an internal absorption over a broad velocity band independent of the pulsational phase. We attribute this absorption to a circumstellar 'shell'. This 'shell' appears to be seen also as spatially extended emission in the O I line at 1300 angstrom, which is probably excited by resonance with Ly beta.

  20. Dwarf Cepheids in the Carina Dwarf Spheroidal Galaxy

    CERN Document Server

    Mateo, M; Nemec, J; Mateo, Mario; Hurley-Keller, Denise; Nemec, James

    1998-01-01

    We have discovered 20 dwarf Cepheids (DC) in the Carina dSph galaxy from the analysis of individual CCD images obtained for a deep photometric study of the system. These short-period pulsating variable stars are by far the most distant (~100 kpc) and faintest (V ~ 23.0) DCs known. The Carina DCs obey a well-defined period-luminosity relation, allowing us to readily distinguish between overtone and fundamental pulsators in nearly every case. Unlike RR Lyr stars, the pulsation mode turns out to be uncorrelated with light-curve shape, nor do the overtone pulsators tend towards shorter periods compared to the fundamental pulsators. Using the period-luminosity (PL) relations from Nemec et al. (1994 AJ, 108, 222) and McNamara (1995, AJ, 109, 1751), we derive (m-M)_0 = 20.06 +/- 0.12, for E(B-V) = 0.025 and [Fe/H] = -2.0, in good agreement with recent, independent estimates of the distance/reddening of Carina. The error reflects the uncertainties in the DC distance scale, and in the metallicity and reddening of Cari...

  1. Estimation of the Galactic Spiral Pattern Speed from Cepheids

    CERN Document Server

    Bobylev, V V; 10.1134/S1063773712100015

    2012-01-01

    To study the peculiarities of the Galactic spiral density wave, we have analyzed the space velocities of Galactic Cepheids with proper motions from the Hipparcos catalog and line-of-sight velocities from various sources. First, based on the entire sample of 185 stars and taking $R_0 = 8$ kpc, we have found the components of the peculiar solar velocity $(u_\\odot,v_\\odot,w_\\odot)=(7.6,11.6,6.1)\\pm(0.8,1.1,0.6)$ km s$^{-1}$, the angular velocity of Galactic rotation $\\Omega_0 = -27.4\\pm0.6$ km s$^{-1}$ kpc$^{-1}$ and its derivatives $\\Omega^{'}_0 = +4.07\\pm0.21,$ km s$^{-1}$ kpc$^{-2}$ and $\\Omega^{"}_0 = -0.83\\pm0.17,$ km s$^{-1}$ kpc$^{-3}$, the amplitudes of the velocity perturbations in the spiral density wave $f_R=-6.7\\pm0.7$ and $f_\\theta= 3.5\\pm0.5$ km s$^{-1}$, the pitch angle of a two-armed spiral pattern (m = 2) $i=-4.5\\pm0.1^\\circ$ (which corresponds to a wavelength $\\lambda=2.0\\pm0.1$ kpc), and the phase of the Sun in the spiral density wave $\\chi_\\odot=-191\\pm5^\\circ$. The phase $\\chi_\\odot$ has bee...

  2. Alessi 95 and the short period Cepheid SU Cassiopeiae

    CERN Document Server

    Turner, David G; Lane, David J; Balam, David D; Gieren, Wolfgang P; Storm, Jesper; Forbes, Doug W; Havlen, Robert J; Alessi, Bruno

    2012-01-01

    The parameters for the newly-discovered open cluster Alessi 95 are established on the basis of available photometric and spectroscopic data, in conjunction with new observations. Colour excesses for spectroscopically-observed B and A-type stars near SU Cas follow a reddening relation described by E(U-B)/E(B-V)=0.83+0.02*E(B-V), implying a value of R=Av/E(B-V)~2.8 for the associated dust. Alessi 95 has a mean reddening of E(B-V)_(B0)=0.35+-0.02 s.e., an intrinsic distance modulus of Vo-Mv=8.16+-0.04 s.e. (+-0.21 s.d.), d=429+-8 pc, and an estimated age of 10^8.2 yr from ZAMS fitting of available UBV, CCD BV, NOMAD, and 2MASS JHKs observations of cluster stars. SU Cas is a likely cluster member, with an inferred space reddening of E(B-V)=0.33+-0.02 and a luminosity of =-3.15+-0.07 s.e., consistent with overtone pulsation (P_FM=2.75 d), as also implied by the Cepheid's light curve parameters, rate of period increase, and Hipparcos parallaxes for cluster stars. There is excellent agreement of the distance estimat...

  3. The One-Zone Model of Cepheid's Pulsations by Zhevakin, Reconsidered

    CERN Document Server

    Ivanov, Mikhail I

    2014-01-01

    The one-zone model of non-adiabatic radial stellar pulsations is considered. Contrary to the original Zhevakin's work the triple-alpha process is the basic thermonuclear fusion reaction within the star under investigation. The model has four dimensionless numbers. For real Cepheids, the magnitude of each of these dimensionless numbers is estimated. It is found that dimensionless numbers associated with both radiation confinement and thermonuclear energy generation are sufficiently less than 1, that is, pure hydrodynamic effects prevail in the model studied. For this case, the model system reduces to the well-known equation of Bhatnagar and Kothari, which describes adiabatic radial pulsations. But solutions of this equation do not have many of real Cepheid curve's features (for instance, asymmetry of luminosity curves about mid-period points). Thus, the model under consideration is not satisfactory for describing Cepheid's pulsations. The problem of construction of an adequate simplified model of stellar pulsa...

  4. ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas

    International Nuclear Information System (INIS)

    New X-ray (XMM-Newton) and JHKs (Observatoire du Mont-Mégantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J – H) = 0.08 ± 0.02 and d = 405 ± 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d=414±5(σx-bar)±10 (σ) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (δ Cep, ζ Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H0.

  5. The VMC survey - XX. Identification of new Cepheids in the Small Magellanic Cloud

    Science.gov (United States)

    Moretti, M. I.; Clementini, G.; Ripepi, V.; Marconi, M.; Rubele, S.; Cioni, M.-R. L.; Muraveva, T.; Groenewegen, M. A. T.; Cross, N. J. G.; Ivanov, V. D.; Piatti, A. E.; de Grijs, R.

    2016-06-01

    We present Ks-band light curves for 299 Cepheids in the Small Magellanic Cloud (SMC) of which 288 are new discoveries that we have identified using multi-epoch near-infrared photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.34 to 9.1 d and cover the magnitude interval 12.9 ≤ ≤ 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE. We focus on searching new Cepheids in external regions of the SMC for which complete VMC Ks-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet.

  6. The VMC Survey - XIX. Identification of new Cepheids in the Small Magellanic Cloud

    CERN Document Server

    Moretti, M I; Ripepi, V; Marconi, M; Rubele, S; Cioni, M -R L; Muraveva, T; Groenewegen, M A T; Cross, N J G; Ivanov, V D; Piatti, A E; de Grijs, R

    2015-01-01

    We present Ks-band light curves for 299 new Cepheids in the Small Magellanic Cloud (SMC) that were identified using multi-epoch near-infrared photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.38 to 13.15 days and cover the magnitude interval 12.35 < Ks < 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE. We focus on searching new Cepheids in external regions of the SMC for which complete VMC Ks-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet.

  7. Hubble Space Telescope Snapshot Survey for Resolved Companions of Galactic Cepheids

    Science.gov (United States)

    Evans, Nancy Remage; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Tingle, Evan; Karovska, Margarita; Pillitteri, Ignazio

    2016-05-01

    We have conducted an imaging survey with the Hubble Space Telescope Wide Field Camera 3 (WFC3) of 70 Galactic Cepheids, typically within 1 kpc, with the aim of finding resolved physical companions. The WFC3 field typically covers the 0.1 pc area where companions are expected. In this paper, we identify 39 Cepheids having candidate companions, based on their positions in color-magnitude diagrams, and having separations ⩾ 5'' from the Cepheids. We use follow-up observations of 14 of these candidates with XMM-Newton, and of one of them with ROSAT, to separate X-ray-active young stars (probable physical companions) from field stars (chance alignments). Our preliminary estimate, based on the optical and X-ray observations, is that only 3% of the Cepheids in the sample have wide companions. Our survey easily detects resolved main-sequence companions as faint as spectral type K. Thus the fact that the two most probable companions (those of FF Aql and RV Sco) are earlier than type K is not simply a function of the detection limit. We find no physical companions having separations larger than 4000 au in the X-ray survey. Two Cepheids are exceptions in that they do have young companions at significantly larger separations (δ Cep and S Nor), but both belong to a cluster or a loose association, so our working model is that they are not gravitationally bound binary members, but rather cluster/association members. All of these properties provide constraints on both star formation and subsequent dynamical evolution. The low frequency of true physical companions at separations > 5'' is confirmed by examination of the subset of the nearest Cepheids and also the density of the fields. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  8. V470 Cas and GSC 2901-00089, Two New Double-mode Cepheids

    CERN Document Server

    Khruslov, A V

    2016-01-01

    We present a photometric study of two new double-mode Cepheids, pulsating in the first and second overtones modes: V470 Cas and GSC 2901-00089. For the search of the double-mode variability, we used all available observations from the ROTSE-I/NSVS and SuperWASP online public archives. Our multicolour CCD observations in the B, V and R bands in Johnson's system confirm the double periodicity of these variables. We study period variations of the two stars; variations of the first overtone periods were reliably detected. In addition, we consider the Petersen diagram for the Galactic 1O/2O Cepheids.

  9. Period-color and amplitude-color relations in classical Cepheid variables III: The Large Magellanic Cloud Cepheid models

    CERN Document Server

    Kanbur, S; Kanbur, Shashi; Ngeow, Chow-Choong

    2006-01-01

    Period-colour (PC) and amplitude-colour (AC) relations are studied for the Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the hydrogen ionization front (HIF) - photosphere interaction. LMC models are constructed with pulsation codes that include turbulent convection, and the properties of these models are studied at maximum, mean and minimum light. As with Galactic models, at maximum light the photosphere is located next to the HIF for the LMC models. However very different behavior is found at minimum light. The long period (P>10days) LMC models imply that the photosphere is disengaged from the HIF at minimum light, similar to the Galactic models, but there are some indications that the photosphere is located near the HIF for the short period (P<10 days) LMC models. We also use the updated LMC data to derive empirical PC and AC relations at these phases. Our numerical models are broadly consistent with our theory and the observed data, though we discuss some caveats in the paper....

  10. Cepheid distances from infrared long-baseline interferometry - I. VINCI/VLTI observations of seven Galactic Cepheids

    CERN Document Server

    Kervella, P; Bersier, D F; Mourard, D; Foresto, V C

    2003-01-01

    We report the angular diameter measurements of seven classical Cepheids (X Sgr, eta Aql, W Sgr, zeta Gem, beta Dor, Y Oph and L Car) that we have obtained with the VINCI instrument, installed at ESO's VLT Interferometer (VLTI). We also present reprocessed archive data obtained with the FLUOR/IOTA instrument on zeta Gem, in order to improve the phase coverage of our observations. We obtain average limb darkened angular diameter values of LD(X Sgr) = 1.471 +/- 0.033 mas, LD(eta Aql) = 1.839 +/- 0.028 mas, LD(W Sgr) = 1.312 +/- 0.029 mas, LD(beta Dor) = 1.891 +/- 0.024 mas, LD(zeta Gem) =1.747 +/- 0.061 mas, LD(Y Oph) = 1.437 +/- 0.040 mas and LD(L Car) = 2.988 +/- 0.012 mas. For four of these stars (eta Aql, W Sgr, beta Dor, and L Car) we detect the pulsational variation of their angular diameter. This enables us to compute directly their distances, using a modified version of the Baade-Wesselink method: d(eta Aql) = 276 [+55 -38] pc, d(W Sgr) = 379 [+216 -130] pc, d(beta Dor) = 345 [+175 -80] pc, d(L Car) = 60...

  11. The near-IR Surface Brightness Method applied to six Cepheids in the young LMC cluster NGC1866

    OpenAIRE

    Storm, Jesper; Gieren, Wolfgang P.; Fouque, Pascal; Barnes III, Thomas G.; Gomez, Matias

    2005-01-01

    We present new near-IR light curves for six Cepheids in the young blue LMC cluster NGC1866 as well as high precision radial velocity curves for ten Cepheids in NGC1866 and two in NGC2031. For the six Cepheids in NGC1866 with new J and K light curves we determine distances and absolute magnitudes by applying the near-IR surface brightness method. We find that the formal error estimates on the derived distances are underestimated by about a factor of two. We find excellent agreement between the...

  12. Metallicity effect on the cepheid period-luminosity relation and H-0

    NARCIS (Netherlands)

    Beaulieu, JP

    1998-01-01

    in the first article, we presented a review on the Cepheid PL relation as a tool for measuring distances, and showed the sensitivity of the method to metallicity. Accounting for it brings the recent differing estimates of H-0 into agreement. (C) Academie des Sciences/Elsevier, Paris.

  13. The Baade-Becker-Wesselink technique and the fundamental astrophysical parameters of Cepheids

    CERN Document Server

    Rastorguev, Alexey S; Zabolotskikh, Marina V; Berdnikov, Leonid N; Gorynya, Natalia A

    2012-01-01

    The BBW method remains one of most demanded tool to derive full set of Cepheid astrophysical parameters. Surface brightness version of the BBW technique was preferentially used during last decades to calculate Cepheid radii and to improve PLC relations. Its implementation requires a priory knowledge of Cepheid reddening value. We propose a new version of the Baade--Becker--Wesselink technique, which allows one to independently determine the colour excess and the intrinsic colour of a radially pulsating star, in addition to its radius, luminosity, and distance. It is considered to be a generalization of the Balona light curve modelling approach. The method also allows the function F(CI_0) = BC + 10 log Teff for the class of pulsating stars considered to be calibrated. We apply this technique to a number of classical Cepheids with very accurate light and radial-velocity curves. The new technique can also be applied to other pulsating variables, e.g. RR Lyraes. We discuss also possible dependence of the projecti...

  14. Galactic abundance gradients from Cepheids. α and heavy elements in the outer disk

    NARCIS (Netherlands)

    B. Lemasle; P. François; K. Genovali; V.V. Kovtyukh; G. Bono; L. Inno; C.D. Laney; L. Kaper; M. Bergemann; M. Fabrizio; N. Matsunaga; S. Pedicelli; F. Primas; M. Romaniello

    2013-01-01

    Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. A

  15. Galactic abundance gradients from Cepheids : α and heavy elements in the outer disk

    NARCIS (Netherlands)

    Lemasle, B.; Francois, P.; Genovali, K.; Kovtyukh, V. V.; Bono, G.; Inno, L.; Laney, C. D.; Kaper, L.; Bergemann, M.; Fabrizio, M.; Matsunaga, N.; Pedicelli, S.; Primas, F.; Romaniello, M.

    2013-01-01

    Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. A

  16. Discovery of blue companions to two southern Cepheids: WW Car and FN Vel

    CERN Document Server

    Kovtyukh, V; Chekhonadskikh, F; Lemasle, B; Belik, S

    2015-01-01

    A large number of high-dispersion spectra of classical Cepheids were obtained in the region of the CaII H+K spectral lines. The analysis of these spectra allowed us to detect the presence of a strong Balmer line, H$\\epsilon$, for several Cepheids, interpreted as the signature of a blue companion: the presence of a sufficiently bright blue companion to the Cepheid results in a discernible strengthening of the CaII H + Hepsilon line relative to the CaII K line. We investigated 103 Cepheids, including those with known hot companions (B5-B6 main-sequence stars) in order to test the method. We could confirm the presence of a companion to WW Car and FN Vel (the existence of the former was only suspected before) and we found that these companions are blue hot stars. The method remains efficient when the orbital velocity changes in a binary system cannot be revealed and other methods of binarity detection are not efficient.

  17. DISCOVERY OF A PAIR OF CLASSICAL CEPHEIDS IN AN INVISIBLE CLUSTER BEYOND THE GALACTIC BULGE

    International Nuclear Information System (INIS)

    We report the discovery of a pair of extremely reddened classical Cepheid variable stars located in the Galactic plane behind the bulge, using near-infrared (NIR) time-series photometry from the VISTA Variables in the Vía Láctea Survey. This is the first time that such objects have ever been found in the opposite side of the Galactic plane. The Cepheids have almost identical periods, apparent brightnesses, and colors. From the NIR Leavitt law, we determine their distances with ∼1.5% precision and ∼8% accuracy. We find that they have a same total extinction of A(V)≃32 mag, and are located at the same heliocentric distance of 〈d〉=11.4±0.9 kpc, and less than 1 pc from the true Galactic plane. Their similar periods indicate that the Cepheids are also coeval, with an age of ∼48±3 Myr, according to theoretical models. They are separated by an angular distance of only 18.″3, corresponding to a projected separation of ∼1 pc. Their position coincides with the expected location of the Far 3 kpc Arm behind the bulge. Such a tight pair of similar classical Cepheids indicates the presence of an underlying young open cluster that is both hidden behind heavy extinction and disguised by the dense stellar field of the bulge. All our attempts to directly detect this “invisible cluster” have failed, and deeper observations are needed. (letters)

  18. On the alpha-element gradients of the Galactic thin disk using Cepheids

    CERN Document Server

    Genovali, K; da Silva, R; Bono, G; Fabrizio, M; Bergemann, M; Buonanno, R; Ferraro, I; François, P; Iannicola, G; Inno, L; Laney, C D; Kudritzki, R -P; Matsunaga, N; Nonino, M; Primas, F; Romaniello, M; Urbaneja, M A; Thévenin, F

    2015-01-01

    We present new homogeneous measurements of Na, Al and three alpha-elements (Mg, Si, Ca) for 75 Galactic Cepheids. The abundances are based on high spectral resolution (R ~ 38,000) and high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO VLT. The current measurements were complemented with Cepheid abundances either provided by our group (75) or available in the literature, for a total of 439 Galactic Cepheids. Special attention was given in providing a homogeneous abundance scale for these five elements plus iron (Genovali et al. 2013, 2014). In addition, accurate Galactocentric distances (RG) based on near-infrared photometry are also available for all the Cepheids in the sample (Genovali et al. 2014). They cover a large fraction of the Galactic thin disk (4.1 <= RG <= 18.4 kpc). We found that the above five elements display well defined linear radial gradients and modest standard deviations over the entire range of RG. Moreover, the [element/Fe] abundance ratios are constant acr...

  19. RR Lyrae and Type II Cepheid Variables Adhere to a Common Distance Relation

    CERN Document Server

    Majaess, Daniel J

    2009-01-01

    Preliminary evidence is presented reaffirming that SX Phe, RR Lyrae, and Type II Cepheid variables may be characterized by a common Wesenheit period-magnitude relation, to first order. Reliable distance estimates to RR Lyrae variables and Type II Cepheids are ascertained from a single VI-based reddening-free relation derived recently from OGLE photometry of LMC Type II Cepheids. Distances are computed to RR Lyrae (d~260 pc), and variables of its class in the galaxies IC 1613, M33, Fornax dSph, LMC, SMC, and the globular clusters M3, M15, M54, omega Cen, NGC 6441, and M92. The results are consistent with literature estimates, and in the particular cases of the SMC, M33, and IC 1613, the distances agree with that inferred from classical Cepheids to within the uncertainties: no corrections were applied to account for differences in metallicity. Moreover, no significant correlation was observed between the distances computed to RR Lyrae variables in omega Cen and their metallicity, despite a considerable spread i...

  20. Notes on disentangling of spectra II. Intrinsic line-profile variability due to Cepheid pulsations

    Czech Academy of Sciences Publication Activity Database

    Hadrava, Petr; Šlechta, Miroslav; Škoda, Petr

    2009-01-01

    Roč. 507, č. 1 (2009), s. 397-404. ISSN 0004-6361 R&D Projects: GA MŠk LC06014; GA ČR GA202/09/0772 Institutional research plan: CEZ:AV0Z10030501 Keywords : variable stars * spectroscopic * Cepheids Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.179, year: 2009

  1. PHAT XIII: The Cepheid Period-Luminosity Relation in M31 Based on the PHAT Survey

    CERN Document Server

    Wagner-Kaiser, R; Dalcanton, J J; Williams, B F; Dolphin, A

    2015-01-01

    Using Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) and Wide Field Camera 3 (WFC3) observations from the Panchromatic Hubble Andromeda Treasury (PHAT), we present new period-luminosity relations for Cepheid variables in M31. Cepheid from several ground-based studies are identified in the PHAT pho- tometry to derive new Period-Luminosity and Wesenheit Period-Luminosity relations in the NIR and visual filters. We derive a distance modulus to M31 of 24.51+/-0.08 in the IR bands and 24.32+/-0.09 in the visual bands, including the first PL relations in the F475W and F814W filters for M31. Our derived visual and IR distance moduli dis- agree at slightly more than a 1-{\\sigma} level. Differences in the Period-Luminosity relations between ground-based and HST observations are investigated for a subset of Cepheids. We find a significant discrepancy between ground-based and HST Period-Luminosity relations with the same Cepheids, suggesting adverse effects from photometric contam- ination in ground-based ...

  2. On the neutron-capture elements across the Galactic thin disk using Cepheids

    CERN Document Server

    da Silva, R; Bono, G; Genovali, K; McWilliam, A; Cristallo, S; Bergemann, M; Buonanno, R; Fabrizio, M; Ferraro, I; Francois, P; Iannicola, G; Inno, L; Laney, C D; Kudritzki, R -P; Matsunaga, N; Nonino, M; Primas, F; Przybilla, N; Romaniello, M; Thevenin, F; Urbaneja, M A

    2015-01-01

    We present new accurate abundances for five neutron-capture (Y, La, Ce, Nd, Eu) elements in 73 classical Cepheids located across the Galactic thin disk. Individual abundances are based on high spectral resolution (R ~ 38,000) and high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO VLT for the DIONYSOS project. Taking account for similar Cepheid abundances provided either by our group (111 stars) or available in the literature, we end up with a sample of 435 Cepheids covering a broad range in iron abundances (-1.6 < [Fe/H] < 0.6). We found, using homogeneous individual distances and abundance scales, well defined gradients for the above elements. However, the slope of the light s-process element (Y) is at least a factor of two steeper than the slopes of heavy s- (La, Ce, Nd) and r- (Eu) process elements. The s to r abundance ratio ([La/Eu]) of Cepheids shows a well defined anticorrelation with of both Eu and Fe. On the other hand, Galactic field stars attain an almost constant va...

  3. EROS differential studies of Cepheids in the Magellanic Clouds : Stellar pulsation, stellar evolution and distance scale

    NARCIS (Netherlands)

    Beaulieu, J. P.; Sasselov, D. D.

    1996-01-01

    Abstract: We present a differential study of 500 Magellanic Cepheids with 3 million measurements obtained as a by-product of the EROS microlensing survey. The data-set is unbiased and provides an excellent basis for a differential analysis between LMC and SMC. We investigate the pulsational properti

  4. Characterizing Binary Properties of $5\\, M_\\odot$ Stars: New Approaches Using Cepheids

    CERN Document Server

    Evans, Nancy Remage

    2014-01-01

    Cepheids provide approaches to determining binary parameters which are often complementary to those for main sequence massive and intermediate mass stars. Specifically, we are using high resolution imaging, radial velocities, and X-ray studies to determine binary characteristics. Among the results are that they have both a high frequency of binary systems, and also a high proportion of triple systems.

  5. On the α-element gradients of the Galactic thin disk using Cepheids

    Science.gov (United States)

    Genovali, K.; Lemasle, B.; da Silva, R.; Bono, G.; Fabrizio, M.; Bergemann, M.; Buonanno, R.; Ferraro, I.; François, P.; Iannicola, G.; Inno, L.; Laney, C. D.; Kudritzki, R.-P.; Matsunaga, N.; Nonino, M.; Primas, F.; Romaniello, M.; Urbaneja, M. A.; Thévenin, F.

    2015-08-01

    We present new homogeneous measurements of Na, Al, and three α-elements (Mg, Si, Ca) for 75 Galactic Cepheids. The abundances are based on high spectral resolution (R~ 38 000) and high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO VLT. The current measurements were complemented with Cepheid abundances provided by our group (75) or available in the literature, for a total of 439 Galactic Cepheids. Special attention was given to providing a homogeneous abundance scale for these five elements plus iron. In addition, accurate Galactocentric distances (RG) based on near-infrared photometry are also available for all the Cepheids in the sample. They cover a large section of the Galactic thin disk (4.1 ≤RG≤ 18.4 kpc). We found that these five elements display well-defined linear radial gradients and modest standard deviations over the entire range of RG. Moreover, the [element/Fe] abundance ratios are constant across the entire thin disk; only the Ca radial distribution shows marginal evidence of a positive slope. These results indicate that the chemical enrichment history of iron and of the quoted five elements has been quite similar across the four quadrants of the Galactic thin disk. The [element/Fe] ratios are also constant over the entire period range. This empirical evidence indicates that the chemical enrichment of Galactic Cepheids has also been very homogenous within the range in age that they cover (~10-300 Myr). Once again, [Ca/Fe] vs. log P shows a (negative) gradient, since it is underabundant among the youngest Cepheids. Finally, we also find that Cepheid abundances agree quite well with similar abundances for thin and thick disk dwarf stars, and they follow the typical Mg-Al and Na-O correlations. Based on spectra collected with the UVES spectrograph available at the ESO Very Large Telescope (VLT), Cerro Paranal, Chile (ESO Proposals: 081.D-0928(A), PI: S. Pedicelli; 082.D-0901(A), PI: S. Pedicelli; 089.D-0767(C), PI: K

  6. The Cepheids of NGC1866: A Precise Benchmark for the Extragalactic Distance Scale and Stellar Evolution from Modern UBVI Photometry

    CERN Document Server

    Musella, I; Stetson, P B; Raimondo, G; Brocato, E; Molinaro, R; Ripepi, V; Carini, R; Coppola, G; Walker, A R; Welch, D L

    2016-01-01

    We present the analysis of multiband time-series data for a sample of 24 Cepheids in the field of the Large Magellanic Cloud cluster NGC1866. Very accurate BVI VLT photometry is combined with archival UBVI data, covering a large temporal window, to obtain precise mean magnitudes and periods with typical errors of 1-2% and of 1 ppm, respectively. These results represent the first accurate and homogeneous dataset for a substantial sample of Cepheid variables belonging to a cluster and hence sharing common distance, age and original chemical composition. Comparisons of the resulting multiband Period-Luminosity and Wesenheit relations to both empirical and theoretical results for the Large Magellanic Cloud are presented and discussed to derive the distance of the cluster and to constrain the mass-luminosity relation of the Cepheids. The adopted theoretical scenario is also tested by comparison with independent calibrations of the Cepheid Wesenheit zero point based on trigonometric parallaxes and Baade-Wesselink t...

  7. THE ARAUCARIA PROJECT: ACCURATE DETERMINATION OF THE DYNAMICAL MASS OF THE CLASSICAL CEPHEID IN THE ECLIPSING SYSTEM OGLE-LMC-CEP-1812

    International Nuclear Information System (INIS)

    We have analyzed the double-lined eclipsing binary system OGLE-LMC-CEP-1812 in the LMC and demonstrate that it contains a classical fundamental mode Cepheid pulsating with a period of 1.31 days. The secondary star is a stable giant. We derive the dynamical masses for both stars with an accuracy of 1.5%, making the Cepheid in this system the second classical Cepheid with a very accurate dynamical mass determination, following the OGLE-LMC-CEP-0227 system studied by Pietrzyński et al. The measured dynamical mass agrees very well with that predicted by pulsation models. We also derive the radii of both components and accurate orbital parameters for the binary system. This new, very accurate dynamical mass for a classical Cepheid will greatly contribute to the solution of the Cepheid mass discrepancy problem, and to our understanding of the structure and evolution of classical Cepheids.

  8. Period-Luminosity relations derived from the OGLE-III first-overtone mode Cepheids in the Magellanic Clouds

    Science.gov (United States)

    Bhardwaj, Anupam; Ngeow, Chow-Choong; Kanbur, Shashi M.; Singh, Harinder P.

    2016-06-01

    We present multiband Period-Luminosity (PL) relations for first-overtone mode Cepheids in the Small Magellanic Cloud (SMC). We derive optical band PL relations and the Wesenheit function using VI mean magnitudes from the Optical Gravitational Lensing Experiment (OGLE-III) survey. We cross-match OGLE-III first-overtone mode Cepheids to the 2MASS and SAGE-SMC catalogues to derive PL relations at near-infrared (JHKs) and mid-infrared (3.6 and 4.5 μm) wavelengths. We test for possible non-linearities in these PL relations using robust statistical tests and find a significant break only in the optical band PL relations at 2.5 d for first-overtone mode Cepheids. We do not find statistical evidence for a non-linearity in these PL relations at 1 d. The multiband PL relations for fundamental-mode Cepheids in the SMC also exhibit a break at 2.5 d. We suggest that the period break around 2.5 d is related to sharp changes in the light-curve parameters for SMC Cepheids. We also derive new optical and mid-infrared band PL relations for first-overtone mode Cepheids in the Large Magellanic Cloud (LMC). We compare multiband PL relations for first-overtone mode Cepheids in the Magellanic Clouds and find a significant difference in the slope of the V-band PL relations but not for I-band PL relations. The slope of PL relations are found to be consistent in most of the infrared bands. A relative distance modulus of Δμ = 0.49 ± 0.02 mag between the two clouds is estimated using multiband PL relations for the first-overtone mode Cepheids in the SMC and LMC.

  9. Hubble Space Telescope Snapshot Survey for Resolved Companions of Galactic Cepheids

    Science.gov (United States)

    Remage Evans, Nancy; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Tingle, Evan; Karovska, Margarita; Pillitteri, Ignazio

    2016-05-01

    We have conducted an imaging survey with the Hubble Space Telescope Wide Field Camera 3 (WFC3) of 70 Galactic Cepheids, typically within 1 kpc, with the aim of finding resolved physical companions. The WFC3 field typically covers the 0.1 pc area where companions are expected. In this paper, we identify 39 Cepheids having candidate companions, based on their positions in color–magnitude diagrams, and having separations ≥slant 5\\prime\\prime from the Cepheids. We use follow-up observations of 14 of these candidates with XMM-Newton, and of one of them with ROSAT, to separate X-ray-active young stars (probable physical companions) from field stars (chance alignments). Our preliminary estimate, based on the optical and X-ray observations, is that only 3% of the Cepheids in the sample have wide companions. Our survey easily detects resolved main-sequence companions as faint as spectral type K. Thus the fact that the two most probable companions (those of FF Aql and RV Sco) are earlier than type K is not simply a function of the detection limit. We find no physical companions having separations larger than 4000 au in the X-ray survey. Two Cepheids are exceptions in that they do have young companions at significantly larger separations (δ Cep and S Nor), but both belong to a cluster or a loose association, so our working model is that they are not gravitationally bound binary members, but rather cluster/association members. All of these properties provide constraints on both star formation and subsequent dynamical evolution. The low frequency of true physical companions at separations \\gt 5\\prime\\prime is confirmed by examination of the subset of the nearest Cepheids and also the density of the fields. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  10. Investigating Cepheid $\\ell$ Carinae's Cycle-to-cycle Variations via Contemporaneous Velocimetry and Interferometry

    CERN Document Server

    Anderson, R I; Kervella, P; Breitfelder, J; LeBouquin, J -B; Eyer, L; Gallenne, A; Palaversa, L; Semaan, T; Saesen, S; Mowlavi, N

    2015-01-01

    Baade-Wesselink-type (BW) techniques enable geometric distance measurements of Cepheid variable stars in the Galaxy and the Magellanic clouds. The leading uncertainties involved concern projection factors required to translate observed radial velocities (RVs) to pulsational velocities and recently discovered modulated variability. We carried out an unprecedented observational campaign involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy (Euler/Coralie) to search for modulated variability in the long-period (P $\\sim$ 35.5 d) Cepheid Carinae. We determine highly precise angular diameters from squared visibilities and investigate possible differences between two consecutive maximal diameters, $\\Delta_{\\rm{max}} \\Theta$. We characterize the modulated variability along the line-of-sight using 360 high-precision RVs. Here we report tentative evidence for modulated angular variability and confirm cycle-to-cycle differences of $\\ell$ Carinae's RV variability. Two successive maxima yield $\\Delta_{\\rm...

  11. Multidimensional realistic modelling of Cepheid-like variables. I: Extensions of the ANTARES code

    CERN Document Server

    Mundprecht, Eva; Kupka, Friedrich

    2012-01-01

    We have extended the ANTARES code to simulate the coupling of pulsation with convection in Cepheid-like variables in an increasingly realistic way, in particular in multidimensions, 2D at this stage. Present days models of radially pulsating stars assume radial symmetry and have the pulsation-convection interaction included via model equations containing ad hoc closures and moreover parameters whose values are barely known. We intend to construct ever more realistic multidimensional models of Cepheids. In the present paper, the first of a series, we describe the basic numerical approach and how it is motivated by physical properties of these objects which are sometimes more, sometimes less obvious. - For the construction of appropriate models a polar grid co-moving with the mean radial velocity has been introduced to optimize radial resolution throughout the different pulsation phases. The grid is radially stretched to account for the change of spatial scales due to vertical stratification and a new grid refi...

  12. High resolution spectroscopy for Cepheids distance determination. II. A period- projection factor relation

    CERN Document Server

    Nardetto, N; Mathias, Ph; Fokin, A; Gillet, D

    2008-01-01

    The projection factor is a key quantity for the interferometric Baade-Wesselink (hereafter IBW) and surface-brightness (hereafter SB) methods of determining the distance of Cepheids. Indeed, it allows a consistent combination of angular and linear diameters of the star. We aim to determine consistent projection factors that include the dynamical structure of the Cepheids' atmosphere. Methods. Hydrodynamical models of delta Cep and l Car have been used to validate a spectroscopic method of determining the projection factor. This method, based on the amplitude of the radial velocity curve, is applied to eight stars observed with the HARPS spectrometer. The projection factor is divided into three sub-concepts : (1) a geometrical effect, (2) the velocity gradient within the atmosphere, and (3) the relative motion of the "optical" pulsating photosphere compared to the corresponding mass elements (hereafter fo-g). Both, (1) and (3) are deduced from geometrical and hydrodynamical models, respectively, while (2) is d...

  13. Spectrum of zeta Geminorium cepheid in the lambda lambda 10580-11020 A region

    International Nuclear Information System (INIS)

    The object of investigation is the star S Geminorium. This star is a classical cepheid with the period of 10.15 days and a symmetric curve of brightness. With the visual value varying from 3sup(m),68 to 4sup(m),16 the spectral class of the cepheid changes in the range of F 7 - G3. The class of luminosity is 1 V. S gem has been observed by means of a photojunction single-cascade image converter of the FKT-IA type, installed in a spectrograph of the ASP-2, 50'' telescope in the Crimean astrophysical observatory. 8 spectrograms have been obtained. The results of identification of lines in the spectrum of S gem for the region of 10580-11020 A are presented in table and spectrogram. The error of the intensity values obtained amounts to 10-15%. The results of observations are discussed

  14. Multidimensional realistic modelling of Cepheid-like variables - I. Extensions of the ANTARES code

    Science.gov (United States)

    Mundprecht, Eva; Muthsam, Herbert J.; Kupka, Friedrich

    2013-11-01

    We have extended the ANTARES code to simulate the coupling of pulsation with convection in Cepheid-like variables in an increasingly realistic way, in particular in multidimensions, 2D at this stage. Present-day models of radially pulsating stars assume radial symmetry and have the pulsation-convection interaction included via model equations containing ad hoc closures and moreover parameters whose values are barely known. We intend to construct ever more realistic multidimensional models of Cepheids. In this paper, the first of a series, we describe the basic numerical approach and how it is motivated by physical properties of these objects which are sometimes more, sometimes less obvious. For the construction of appropriate models a polar grid comoving with the mean radial velocity has been introduced to optimize radial resolution throughout the different pulsation phases. The grid is radially stretched to account for the change of spatial scales due to vertical stratification and a new grid refinement scheme is introduced to resolve the upper, hydrogen ionization zone where the gradient of temperature is steepest. We demonstrate that the simulations are not conservative when the original weighted essentially non-oscillatory method implemented in ANTARES is used and derive a new scheme which allows a conservative time evolution. The numerical approximation of diffusion follows the same principles. Moreover, the radiative transfer solver has been modified to improve the efficiency of calculations on parallel computers. We show that with these improvements, the ANTARES code can be used for realistic simulations of the convection-pulsation interaction in Cepheids. We discuss the properties of several numerical models of this kind which include the upper 42 per cent of a Cepheid along its radial coordinate and assume different opening angles. The models are suitable for an in-depth study of convection and pulsation in these objects.

  15. The Detailed Forms of the LMC Cepheid PL and PLC Relations

    OpenAIRE

    Koen, C.; Kanbur, S.; Ngeow, C.

    2007-01-01

    Possible deviations from linearity of the LMC Cepheid PL and PLC relations are investigated. Two datasets are studied, respectively from the OGLE and MACHO projects. A nonparametric test, based on linear regression residuals, suggests that neither PL relation is linear. If colour dependence is allowed for then the MACHO PL relation is found to deviate more significantly from the linear, while the OGLE PL relation is consistent with linearity. These finding are confirmed by fitting "Generalise...

  16. The One-Zone Model of Cepheid's Pulsations by Zhevakin, Reconsidered

    OpenAIRE

    Ivanov, Mikhail I.

    2014-01-01

    The one-zone model of non-adiabatic radial stellar pulsations is considered. Contrary to the original Zhevakin's work the triple-alpha process is the basic thermonuclear fusion reaction within the star under investigation. The model has four dimensionless numbers. For real Cepheids, the magnitude of each of these dimensionless numbers is estimated. It is found that dimensionless numbers associated with both radiation confinement and thermonuclear energy generation are sufficiently less than 1...

  17. Neutron-capture elements across the Galactic thin disk using Cepheids

    Science.gov (United States)

    da Silva, R.; Lemasle, B.; Bono, G.; Genovali, K.; McWilliam, A.; Cristallo, S.; Bergemann, M.; Buonanno, R.; Fabrizio, M.; Ferraro, I.; François, P.; Iannicola, G.; Inno, L.; Laney, C. D.; Kudritzki, R.-P.; Matsunaga, N.; Nonino, M.; Primas, F.; Przybilla, N.; Romaniello, M.; Thévenin, F.; Urbaneja, M. A.

    2016-02-01

    We present new accurate abundances for five neutron-capture elements (Y, La, Ce, Nd, Eu) in 73 classical Cepheids located across the Galactic thin disk. Individual abundances are based on high spectral resolution (R ~ 38 000) and high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO VLT for the DIONYSOS project. Taking into account similar Cepheid abundances provided by our group (111 stars) and available in the literature, we end up with a sample of 435 Cepheids covering a broad range in iron abundances (-1.6 mild enhancement in La only when they approach solar iron abundance. The [Y/Eu] ratio shows slight evidence of a correlation with Eu and, in particular, with iron abundance for field Galactic stars. We also investigated the s-process index ([hs/ls]) and we found a well-defined anticorrelation, as expected, between [La/Y] and iron abundance. Moreover, we found a strong correlation between [La/Y] and [La/Fe] and, in particular, a clear separation between Galactic and Sagittarius red giants. Finally, the comparison between predictions for low-mass asymptotic giant branch stars and the observed[La/Y] ratio indicate a very good agreement over the entire metallicity range covered by Cepheids. However, the observed spread at fixed iron content is larger than predicted by current models. Based on spectra collected with the UVES spectrograph available at the ESO Very Large Telescope (VLT), Cerro Paranal, Chile (ESO Proposals: 081.D-0928(A), PI: S. Pedicelli; 082.D-0901(A), PI: S. Pedicelli; 089.D-0767(C), PI: K. Genovali).Tables 2, 3, 4, and 7 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A125

  18. DISCOVERY OF THE HOST CLUSTER FOR THE FUNDAMENTAL CEPHEID CALIBRATOR ZETA GEMINORUM

    International Nuclear Information System (INIS)

    New and existing CORAVEL, UBVJHKs , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator ζ Gem is a cluster member. The following parameters were inferred for ζ Gem from cluster membership and are tied to new spectral classifications (DAO) established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV): EB–V = 0.02 ± 0.02, log τ = 7.85 ± 0.15, and d = 355 ± 15 pc. The mean distance to ζ Gem from cluster membership and six recent estimates (e.g., IRSB) is d=363±9(σx-bar )±26 (σ) pc. The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. Forthcoming precise proper motions (DASCH) and Chandra/XMM-Newton observations of the broader field may be employed to identify cluster members, bolster the cluster's existence, and provide stronger constraints on the Cepheid's fundamental parameters.

  19. Galactic abundance gradients from Cepheids: alpha and heavy elements in the outer disk

    CERN Document Server

    Lemasle, B; Genovali, K; Kovtyukh, V V; Bono, G; Inno, L; Laney, C D; Kaper, L; Bergemann, M; Fabrizio, M; Matsunaga, N; Pedicelli, S; Primas, F; Romaniello, M

    2013-01-01

    Context: Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the PL relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. Aims: We want to measure the Galactic abundance gradient of several chemical elements. While the slope of the Cepheid iron gradient did not vary much from the very first studies, the gradients of the other elements are not that well constrained. In this paper we focus on the inner and outer regions of the Galactic thin disk. Methods: We use HR spectra (FEROS, ESPADONS, NARVAL) to measure the abundances of several light (Na, Al), alpha (Mg, Si, S, Ca), and heavy elements (Y, Zr, La, Ce, Nd, Eu) in a sample of 65 Milky Way Cepheids. Combining these results with accurate distances from period-Wesenheit relations in the NIR enables us to determine the abundance gradients in the Milky Way. Results: Our results are in good agreement wit...

  20. The influential effect of blending, bump, changing period and eclipsing Cepheids on the Leavitt law

    CERN Document Server

    García-Varela, A; Sabogal, B E; Domínguez, S Vargas; Martínez, J

    2016-01-01

    The investigation of the non-linearity of the Leavitt law is a topic that began more than seven decades ago, when some of the studies in this field found that the Leavitt law has a break at about ten days. The goal of this work is to investigate a possible statistical cause of this non-linearity. By applying linear regressions to OGLE-II and OGLE-IV data, we find that, in order to obtain the Leavitt law by using linear regression, robust techniques to deal with influential points and/or outliers are needed instead of the ordinary least-squares regression traditionally used. In particular, by using $M$- and $MM$-regressions we establish firmly and without doubts the linearity of the Leavitt law in the Large Magellanic Cloud, without rejecting or excluding Cepheid data from the analysis. This implies that light curves of Cepheids suggesting blending, bumps, eclipses or period changes, do not affect the Leavitt law for this galaxy. For the SMC, including this kind of Cepheids, it is not possible to find an adequ...

  1. The OGLE Collection of Variable Stars. Anomalous Cepheids in the Magellanic Clouds

    CERN Document Server

    Soszynski, I; Szymanski, M K; Pietrzynski, G; Wyrzykowski, L; Ulaczyk, K; Poleski, R; Pietrukowicz, P; Kozlowski, S; Skowron, J; Skowron, D; Mroz, P; Pawlak, M

    2015-01-01

    We present a collection of 250 anomalous Cepheids (ACs) discovered in the OGLE-IV fields toward the Large (LMC) and Small Magellanic Cloud (SMC). The LMC sample is an extension of the OGLE-III Catalog of ACs published in 2008, while the SMC sample contains the first known bona fide ACs in this galaxy. The total sample is composed of 141 ACs in the LMC and 109 ACs in the SMC. All these stars pulsate in single modes: fundamental (174 objects) or first overtone (76 objects). Additionally, we report the discovery of four ACs located in the foreground of the Magellanic Clouds. These are the first fundamental-mode ACs known in the Galactic field. We demonstrate that the coefficients phi_21 and phi_31 determined by the Fourier light curve decomposition are useful discriminators between classical Cepheids and ACs, at least in the LMC and in the field of the Milky Way. In the SMC, the light curve shapes and mean magnitudes of short-period classical Cepheids make them similar to ACs, which is a source of difficulties i...

  2. Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations

    CERN Document Server

    Benedict, G F; Feast, M W; Barnes, T G; Harrison, T E; Patterson, R J; Menzies, J W; Bean, J L; Freedman, W L; Arthur, Barbara E. Mc; Feast, Michael W.; Barnes, Thomas G.; Harrison, Thomas E.; Patterson, Richard J.; Menzies, John W.; Bean, Jacob L.; Freedman, Wendy L.

    2006-01-01

    (abridged) We present new absolute trigonometric parallaxes and relative proper motions for nine Galactic Cepheid variable stars: l Car, zeta Gem, beta Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur. We obtain these results with astrometric data from Fine Guidance Sensor 1r, a white-light interferometer on Hubble Space Telescope. We find absolute parallaxes with an average sigma_pi/pi = 8%. Two stars (FF Aql and W Sgr) required the inclusion of binary astrometric perturbations, providing Cepheid mass estimates. With these parallaxes we compute absolute magnitudes in V, I, K, and Wesenheit W_{VI} bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Adding our previous absolute magnitude determination for delta Cep, we construct Period-Luminosity relations for ten Galactic Cepheids. We compare our new Period-Luminosity relations with those adopted by several recent investigations, including the Freedman and Sandage H_0 projects. Adopting our Period-Luminosity relationship would ten...

  3. Period and light-curve fluctuations of the Kepler Cepheid V1154 Cygni

    Science.gov (United States)

    Derekas, A.; Szabó, Gy. M.; Berdnikov, L.; Szabó, R.; Smolec, R.; Kiss, L. L.; Szabados, L.; Chadid, M.; Evans, N. R.; Kinemuchi, K.; Nemec, J. M.; Seader, S. E.; Smith, J. C.; Tenenbaum, P.

    2012-09-01

    We present a detailed period analysis of the bright Cepheid-type variable star V1154 Cygni (V1154 Cyg; V = 9.1 mag, P ≈ 4.9 d) based on almost 600 d of continuous observations by the Kepler space telescope. The data reveal significant cycle-to-cycle fluctuations in the pulsation period, indicating that classical Cepheids may not be as accurate astrophysical clocks as commonly believed: regardless of the specific points used to determine the O - C values, the cycle lengths show a scatter of 0.015-0.02 d over 120 cycles covered by the observations. A very slight correlation between the individual Fourier parameters and the O - C values was found, suggesting that the O - C variations might be due to the instability of the light-curve shape. Random-fluctuation tests revealed a linear trend up to a cycle difference 15, but for long term, the period remains around the mean value. We compare the measurements with simulated light curves that were constructed to mimic V1154 Cyg as a perfect pulsator modulated only by the light travel time effect caused by low-mass companions. We show that the observed period jitter in V1154 Cyg represents a serious limitation in the search for binary companions. While the Kepler data are accurate enough to allow the detection of planetary bodies in close orbits around a Cepheid, the astrophysical noise can easily hide the signal of the light-time effect.

  4. No Evidence for Classical Cepheids and a New Dwarf Galaxy Behind the Galactic Disk

    CERN Document Server

    Pietrukowicz, P; Szymanski, M K; Soszynski, I; Pietrzynski, G; Wyrzykowski, L; Poleski, R; Ulaczyk, K; Skowron, J; Mroz, P; Pawlak, M; Kozlowski, S

    2015-01-01

    Based on data from the ongoing OGLE Galaxy Variability Survey (OGLE GVS) we have verified observed properties of stars detected by the near-infrared VVV survey in a direction near the Galactic plane at longitude l~-27 deg and recently tentatively classified as classical Cepheids belonging to a, hence claimed, dwarf galaxy at a distance of about 90 kpc from the Galactic Center. Three of four stars are detected in the OGLE GVS I-band images. We show that two of the objects are not variable at all and the third one with a period of 5.695 d and a nearly sinusoidal light curve of an amplitude of 0.5 mag cannot be a classical Cepheid and is very likely a spotted object. These results together with a very unusual shape of the Ks-band light curve of the fourth star indicate that very likely none of them is a Cepheid and, thus, there is no evidence for a background dwarf galaxy. Our observations show that a great care must be taken when classifying objects by their low-amplitude close-to-sinusoidal near-infrared light...

  5. The Influential Effect of Blending, Bump, Changing Period, and Eclipsing Cepheids on the Leavitt Law

    Science.gov (United States)

    García-Varela, A.; Muñoz, J. R.; Sabogal, B. E.; Vargas Domínguez, S.; Martínez, J.

    2016-06-01

    The investigation of the nonlinearity of the Leavitt law (LL) is a topic that began more than seven decades ago, when some of the studies in this field found that the LL has a break at about 10 days. The goal of this work is to investigate a possible statistical cause of this nonlinearity. By applying linear regressions to OGLE-II and OGLE-IV data, we find that to obtain the LL by using linear regression, robust techniques to deal with influential points and/or outliers are needed instead of the ordinary least-squares regression traditionally used. In particular, by using M- and MM-regressions we establish firmly and without doubt the linearity of the LL in the Large Magellanic Cloud, without rejecting or excluding Cepheid data from the analysis. This implies that light curves of Cepheids suggesting blending, bumps, eclipses, or period changes do not affect the LL for this galaxy. For the Small Magellanic Cloud, when including Cepheids of this kind, it is not possible to find an adequate model, probably because of the geometry of the galaxy. In that case, a possible influence of these stars could exist.

  6. Variable stars in nearby galaxies; 1, Search for Cepheids in Field A of IC 1613

    CERN Document Server

    Antonello, E; Fugazza, D; Bossi, M; Covino, S

    1999-01-01

    The first results are presented of a four-year program dedicated to the CCD observations of Cepheids in the nearby galaxy IC 1613. Since the program was carried out with a relatively small telescope, the Dutch 0.9 m at ESO-La Silla, the observations were performed without filter (white light), or Wh-band; the advantage of this technique is that the photon statistics correspond to that of V-band observations made with larger telescopes than 2 m and similar exposure time. The effective wavelength of the Wh-band is intermediate between that of V and R bands for stars of A-G spectral type, for back-illuminated CCD detectors. The analysis of the observations of Field A revealed the presence of about 110 variable stars. The detected population I Cepheids are 43; 9 Cepheids were already known from previous works, while most of the new stars have a short period P. For stars with P > 5 d and sufficient phase coverage it is possible to perform good Fourier decomposition of light curves with resulting standard deviation...

  7. The Araucaria Project: the First-overtone Classical Cepheid in the Eclipsing System OGLE-LMC-CEP-2532

    Science.gov (United States)

    Pilecki, Bogumił; Graczyk, Dariusz; Gieren, Wolfgang; Pietrzyński, Grzegorz; Thompson, Ian B.; Smolec, Radosław; Udalski, Andrzej; Soszyński, Igor; Konorski, Piotr; Taormina, Mónica; Gallenne, Alexandre; Minniti, Dante; Catelan, Márcio

    2015-06-01

    We present here the first spectroscopic and photometric analysis of the double-lined eclipsing binary containing the classical, first-overtone (FO) Cepheid OGLE-LMC-CEP-2532 (MACHO 81.8997.87). The system has an orbital period of 800 days and the Cepheid is pulsating with a period of 2.035 days. Using spectroscopic data from three high-class telescopes and photometry from three surveys spanning 7500 days, we are able to derive the dynamical masses for both stars with an accuracy better than 3%. This makes the Cepheid in this system one of a few classical Cepheids with an accurate dynamical mass determination ({{M}1}=3.90+/- 0.10 {{M}⊙ }). The companion is probably slightly less massive (3.82+/- 0.10 {{M}⊙ }), but may have the same mass within errors ({{M}2}/{{M}1}=0.981+/- 0.015). The system has an age of about 185 million years and the Cepheid is in a more advanced evolutionary stage. For the first time precise parameters are derived for both stars in this system. Due to the lack of the secondary eclipse for many years, not much was known about the Cepheid’s companion. In our analysis, we used extra information from the pulsations and the orbital solution from the radial velocity curve. The best model predicts a grazing secondary eclipse shallower than 1 mmag, hence undetectable in the data, about 370 days after the primary eclipse. The dynamical mass obtained here is the most accurate known for a FO Cepheid and will contribute to the solution of the Cepheid mass discrepancy problem. The research is based on observations obtained with the ESO VLT and 3.6 m telescopes for Programmes 092.D-0295(A), 091.D-0393(A), 089.D-0330(A), 088.D-0447(A), 086.D-0103(A), and 085.D-0398(A), and with the Magellan Clay and Warsaw telescopes at Las Campanas Observatory.

  8. THREE-DIMENSIONAL MAPS OF THE MAGELLANIC CLOUDS USING RR LYRAE STARS AND CEPHEIDS. I. THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    The new data for Cepheids and RR Lyrae stars of the Optical Gravitational Lensing Experiment (OGLE III) survey allow us to study the three-dimensional distribution of stars corresponding to young (a few tens to a few hundreds of millions of years) and old (typically older than ∼9 Gyr) populations of the Large Magellanic Cloud (LMC) traced by these variable stars. We estimate the distance to 16,949 RR Lyrae stars by using their photometrically estimated metallicities. Furthermore, the periods of 1849 Cepheids are used to determine their distances. Three-dimensional maps are obtained by using individual reddening estimates derived from the intrinsic color of these stars. The resulting median distances of the RR Lyrae stars and Cepheids appear to resolve the long and short distance scale problem for our sample. With median distances of 53.1 ± 3.2 kpc for the RR Lyrae stars and 53.9 ± 1.8 kpc for the Cepheids, these two distance indicators are in very good agreement with each other in contrast to a number of earlier studies. Individual reddening estimates allow us to resolve the distance discrepancies often observed while comparing Cepheids and RR Lyrae stars. For both stellar populations we find the inclination angle of the LMC to be 32° ± 4° and the mean position angle to be 115° ± 15°. The position angle increases with galactocentric radius, indicative of mild twisting. Within the innermost 7° of the LMC covered by OGLE III, the change in position angle amounts to more than 10°. The depth of the Cepheids is found to be 1.7 ± 0.2 kpc. The bar stands out as an overdensity both in RR Lyrae stars and in Cepheids. In RR Lyrae stars the bar can be traced as a protruding overdensity with a line-of-sight depth of almost 5 kpc in front of the main body of the disk.

  9. OGLE-ing the Magellanic System: Three-dimensional structure of the Clouds and the Bridge using classical Cepheids

    CERN Document Server

    Jacyszyn-Dobrzeniecka, Anna M; Mróz, P; Skowron, J; Soszyński, I; Udalski, A; Pietrukowicz, P; Kozłowski, S; Wyrzykowski, Ł; Poleski, R; Pawlak, M; Szymański, M K; Ulaczyk, K

    2016-01-01

    We analyzed a sample of 9418 fundamental-mode and first-overtone classical Cepheids from the OGLE-IV Collection of Classical Cepheids. The distance to each Cepheid was calculated using the period-luminosity relation for the Wesenheit magnitude, fitted to our data. The classical Cepheids in the LMC are situated mainly in the bar and in the northern arm. The eastern part of the LMC is closer to us and the plane fit to the whole LMC sample yields the inclination i=24.2+-0.6 deg and position angle P.A.=151.4+-1.5 deg. We redefined the LMC bar by extending it in the western direction and found no offset from the plane of the LMC contrary to previous studies. On the other hand, we found that the northern arm is offset from a plane by about -0.5 kpc, which was not observed before. The age distribution of the LMC Cepheids shows one maximum at about 100 Myr. We demonstrate that the SMC has a non-planar structure and can be described as an extended ellipsoid. We identified two large ellipsoidal off-axis structures in t...

  10. The Araucaria Project: The First-Overtone Classical Cepheid in the Eclipsing System OGLE-LMC-CEP-2532

    CERN Document Server

    Pilecki, B; Gieren, W; Pietrzyński, G; Thompson, I B; Smolec, R; Udalski, A; Soszyński, I; Konorski, P; Taormina, M; Gallenne, A; Minniti, D; Catelan, M

    2015-01-01

    We present here the first spectroscopic and photometric analysis of the double-lined eclipsing binary containing the classical, first-overtone Cepheid OGLE-LMC-CEP-2532 (MACHO 81.8997.87). The system has an orbital period of 800 days and the Cepheid is pulsating with a period of 2.035 days. Using spectroscopic data from three high-class telescopes and photometry from three surveys spanning 7500 days we are able to derive the dynamical masses for both stars with an accuracy better than 3%. This makes the Cepheid in this system one of a few classical Cepheids with an accurate dynamical mass determination (M_1=3.90 +/- 0.10 M_sun). The companion is probably slightly less massive (3.82 +/- 0.10 M_sun), but may have the same mass within errors (M_2/M_1= 0.981 +/- 0.015). The system has an age of about 185 million years and the Cepheid is in a more advanced evolutionary stage. For the first time precise parameters are derived for both stars in this system. Due to the lack of the secondary eclipse for many years not...

  11. Period-Luminosity relations derived from the OGLE-III First-overtone mode Cepheids in the Magellanic Clouds

    CERN Document Server

    Bhardwaj, Anupam; Kanbur, Shashi M; Singh, Harinder P

    2016-01-01

    We present multi-band Period-Luminosity (PL) relations for first-overtone mode Cepheids in the Small Magellanic Cloud (SMC). We derive optical band PL relations and the Wesenheit function using $VI$ mean magnitudes from the Optical Gravitational Lensing Experiment (OGLE-III) survey. We cross-match OGLE-III first-overtone mode Cepheids to the 2MASS and SAGE-SMC catalogs to derive PL relations at near-infrared ($JHK_s$) and mid-infrared ($3.6~\\&~4.5\\mu\\mathrm{m}$) wavelengths. We test for possible non-linearities in these PL relations using robust statistical tests and find a significant break only in the optical-band PL relations at 2.5 days for first-overtone mode Cepheids. We do not find statistical evidence for a non-linearity in these PL relations at 1 day. The multi-band PL relations for fundamental-mode Cepheids in the SMC also exhibit a break at 2.5 days. We suggest that the period break around 2.5 days is related to sharp changes in the light curve parameters for SMC Cepheids. We also derive new op...

  12. ON THE DISTANCE OF THE MAGELLANIC CLOUDS USING CEPHEID NIR AND OPTICAL-NIR PERIOD-WESENHEIT RELATIONS

    International Nuclear Information System (INIS)

    We present the largest near-infrared (NIR) data sets, JHKs, ever collected for classical Cepheids in the Magellanic Clouds (MCs). We selected fundamental (FU) and first overtone (FO) pulsators, and found 4150 (2571 FU, 1579 FO) Cepheids for Small Magellanic Cloud (SMC) and 3042 (1840 FU, 1202 FO) for Large Magellanic Cloud (LMC). Current sample is 2-3 times larger than any sample used in previous investigations with NIR photometry. We also discuss optical VI photometry from OGLE-III. NIR and optical-NIR Period-Wesenheit (PW) relations are linear over the entire period range (0.0 FU ≤ 1.65) and their slopes are, within the intrinsic dispersions, common between the MCs. These are consistent with recent results from pulsation models and observations suggesting that the PW relations are minimally affected by the metal content. The new FU and FO PW relations were calibrated using a sample of Galactic Cepheids with distances based on trigonometric parallaxes and Cepheid pulsation models. By using FU Cepheids we found a true distance moduli of 18.45 ± 0.02(random) ± 0.10(systematic) mag (LMC) and 18.93 ± 0.02(random) ± 0.10(systematic) mag (SMC). These estimates are the weighted mean over 10 PW relations and the systematic errors account for uncertainties in the zero point and in the reddening law. We found similar distances using FO Cepheids (18.60 ± 0.03(random) ± 0.10(systematic) mag (LMC) and 19.12 ± 0.03(random) ± 0.10(systematic) mag (SMC)). These new MC distances lead to the relative distance, Δμ = 0.48 ± 0.03 mag (FU, log P = 1) and Δμ = 0.52 ± 0.03 mag (FO, log P = 0.5), which agrees quite well with previous estimates based on robust distance indicators.

  13. Intrinsic B-V color for galactic cepheids and some comments on the Sandage-Tammann relationship

    Science.gov (United States)

    Kelsall, T.

    1972-01-01

    Transformations are found for converting the b-y color excesses for Cepheids given by Williams (1966) and Kelsall (1971) into B-V excesses. The combination of these results with the E(B-V)'s determined by Sandage and Tammann (1971) gives precise data for eighty-eight galactic Cepheids. The period-color and period-color-(amplitude defect) relationships, that are germane to the LogP intervals 0.4 to 1.4 and 0.4 to 1.3, respectively, are found.

  14. The VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulge

    CERN Document Server

    Dékány, I; Majaess, D; Zoccali, M; Hajdu, G; Alonso-García, J; Catelan, M; Gieren, W; Borissova, J

    2015-01-01

    Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy's evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years.

  15. The VVV Survey Reveals Classical Cepheids Tracing a Young and Thin Stellar Disk across the Galaxy’s Bulge

    Science.gov (United States)

    Dékány, I.; Minniti, D.; Majaess, D.; Zoccali, M.; Hajdu, G.; Alonso-García, J.; Catelan, M.; Gieren, W.; Borissova, J.

    2015-10-01

    Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy’s evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years.

  16. Galactic abundance gradients from Cepheids. α and heavy elements in the outer disk

    Science.gov (United States)

    Lemasle, B.; François, P.; Genovali, K.; Kovtyukh, V. V.; Bono, G.; Inno, L.; Laney, C. D.; Kaper, L.; Bergemann, M.; Fabrizio, M.; Matsunaga, N.; Pedicelli, S.; Primas, F.; Romaniello, M.

    2013-10-01

    Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. Aims: We want to measure the Galactic abundance gradient of several chemical elements. While the slope of the Cepheid iron gradient did not vary much from the very first studies, the gradients of the other elements are not that well constrained. In this paper we focus on the inner and outer regions of the Galactic thin disk. Methods: We use high-resolution spectra (FEROS, ESPADONS, NARVAL) to measure the abundances of several light (Na, Al), α (Mg, Si, S, Ca), and heavy elements (Y, Zr, La, Ce, Nd, Eu) in a sample of 65 Milky Way Cepheids. Combining these results with accurate distances from period-Wesenheit relations in the near-infrared enables us to determine the abundance gradients in the Milky Way. Results: Our results are in good agreement with previous studies on either Cepheids or other tracers. In particular, we confirm an upward shift of ≈0.2 dex for the Mg abundances, as has recently been reported. We also confirm the existence of a gradient for all the heavy elements studied in the context of a local thermodynamic equilibrium analysis. However, for Y, Nd, and especially La, we find lower abundances for Cepheids in the outer disk than reported in previous studies, leading to steeper gradients. This effect can be explained by the differences in the line lists used by different groups. Conclusions: Our data do not support a flattening of the gradients in the outer disk, in agreement with recent Cepheid studies and chemo-dynamical simulations. This is in contrast to the open cluster observations but remains compatible with a picture where the transition zone between the inner disk and the outer disk would move outward with time. Based on observations obtained

  17. The role of negative buoyancy in convective Cepheid models. Double-mode pulsations revisited

    CERN Document Server

    Smolec, R

    2008-01-01

    The longstanding problem of modeling double-mode behaviour of classical pulsators was solved with the incorporation of turbulent convection into pulsation hydrocodes. However, the reasons for the computed double-mode behaviour were never clearly identified. In our recent papers (Smolec & Moskalik 2008a,b) we showed that the double-mode behaviour results from the neglect of negative buoyancy effects in some of the hydrocodes. If these effects are taken into account, no stable non-resonant double-mode behaviour can be found. In these proceedings we focus our attention on the role of negative buoyancy effects in classical Cepheid models.

  18. Type II Cepheids in the Milky Way disc. Chemical composition of two new W Vir stars: DD Vel and HQ Car

    CERN Document Server

    Lemasle, B; Bono, G; François, P; Saviane, I; Yegorova, I; Genovali, K; Inno, L; Galazutdinov, G; da Silva, R

    2015-01-01

    A robust classification of Cepheids into their different sub-classes and, in particular, between classical and Type II Cepheids, is necessary to properly calibrate the period-luminosity relations and for populations studies in the Galactic disc. Type II Cepheids are, however, very diverse, and classifications based either on intrinsic (period, light curve) or external parameters (e.g., [Fe/H], |z|) do not provide a unique classification. We want to ascertain the classification of two Cepheids, HQ Car and DD Vel, that are sometimes classified as classical Cepheids and sometimes as Type II Cepheids. To achieve this goal, we examine both their chemical composition and the presence of specific features in their spectra. We find emission features in the H{\\alpha} and in the 5875.64 {\\AA} He I lines that are typical of W Vir stars. The [Na/Fe] (or [Na/Zn]) abundances are typical of thick-disc stars, while BL Her stars are Na-overabundant ([Na/Fe]>+0.5 dex). Finally, the two Cepheids show a possible (HQ Car) or prob...

  19. The ARAUCARIA project. OGLE-LMC-CEP-1718: An exotic eclipsing binary system composed of two classical overtone cepheids in a 413 day orbit

    Energy Technology Data Exchange (ETDEWEB)

    Gieren, Wolfgang; Pilecki, Bogumił; Pietrzyński, Grzegorz; Graczyk, Dariusz; Gallenne, Alexandre, E-mail: wgieren@astro-udec.cl, E-mail: pietrzyn@astrouw.edu.pl, E-mail: darek@astro-udec.cl, E-mail: dgallenne@astro-udec.cl, E-mail: bpilecki@astro-udec.cl [Departamento de Astronomia, Universidad de Concepción, Casilla 160-C, Concepción (Chile); and others

    2014-05-10

    We have obtained extensive high-quality spectroscopic observations of the OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud that Soszyński et al. had identified as a candidate system for containing two classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary motion of the Cepheids in a 413 day eccentric orbit, rendering this eclipsing binary system the first ever known to consist of 2 classical Cepheid variables. After disentangling the four different radial velocity variations in the system, we present the orbital solution and the individual pulsational radial velocity curves of the Cepheids. We show that both Cepheids are extremely likely to be first overtone pulsators and determine their respective dynamical masses, which turn out to be equal to within 1.5%. Since the secondary eclipse is not observed in the orbital light curve, we cannot derive the individual radii of the Cepheids, but the sum of their radii derived from the photometry is consistent with overtone pulsation for both variables. The existence of two equal-mass Cepheids in a binary system having different pulsation periods (1.96 and 2.48 days, respectively) may pose an interesting challenge to stellar evolution and pulsation theories, and a more detailed study of this system using additional data sets should yield deeper insight about the physics of stellar evolution of Cepheid variables. Future analysis of the system using additional near-infrared photometry might also lead to a better understanding of the systematic uncertainties in current Baade-Wesselink techniques of distance determinations to Cepheid variables.

  20. A long-period Cepheid variable in the starburst cluster VdBH222

    CERN Document Server

    Clark, J S; Lohr, M E; Dorda, R; González-Fernández, C; Lewis, F; Roche, P

    2015-01-01

    Galactic starburst clusters play a twin role in astrophysics, serving as laboratories for the study of stellar physics and also delineating the structure and recent star formation history of the Milky Way. In order to exploit these opportunities we have undertaken a multi-epoch spectroscopic survey of the red supergiant dominated young massive clusters thought to be present at both near and far ends of the Galactic Bar. Significant spectroscopic variability suggestive of radial pulsations was found for the yellow supergiant VdBH 222 #505. Follow-up photometric investigations revealed modulation with a period of ~23.325d; both timescale and pulsational profile are consistent with a Cepheid classification. As a consequence #505 may be recognised as one of the longest period Galactic cluster Cepheids identified to date and hence of considerable use in constraining the bright end of the period/luminosity relation at solar metallicities. In conjunction with extant photometry we infer a distance of ~6kpc for VdBH22...

  1. Bimodal chemical evolution of the Galactic disk and the Barium abundance of Cepheids

    CERN Document Server

    Lepine, Jacques R D; Barros, Douglas A; Junqueira, Thiago C; Scarano, Sergio

    2013-01-01

    In order to understand the Barium abundance distribution in the Galactic disk based on Cepheids, one must first be aware of important effects of the corotation resonance, situated a little beyond the solar orbit. The thin disk of the Galaxy is divided in two regions that are separated by a barrier situated at that radius. Since the gas cannot get across that barrier, the chemical evolution is independent on the two sides of it. The barrier is caused by the opposite directions of flows of gas, on the two sides, in addition to a Cassini-like ring void of HI (caused itself by the flows). A step in the metallicity gradient developed at corotation, due to the difference in the average star formation rate on the two sides, and to this lack of communication between them. In connection with this, a proof that the spiral arms of our Galaxy are long-lived (a few billion years) is the existence of this step. When one studies the abundance gradients by means of stars which span a range of ages, like the Cepheids, one has...

  2. V1135 Herculis: a double-lined eclipsing binary with an Anomalous Cepheid

    CERN Document Server

    Sipahi, E; Cakirli, O; Dal, H A; Evren, S

    2013-01-01

    BVR light curves and radial velocities for the double-lined eclipsing binary V1135\\,Her were obtained. The brighter component of V1135\\,Her is a Cepheid variable with a pulsation period of 4.22433$\\pm$0.00026 days. The orbital period of the system is about 39.99782$\\pm$0.00233 days, which is the shortest value among the known Type\\,II Cepheid binaries. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained. Our analyses of the multi-colour light curves and radial velocities led to the determination of fundamental stellar properties of both components of the interesting system V1135\\,Her. The system consists of two evolved stars, G1+K3 between giants and supergiants, with masses of M$_1$=1.461$\\pm$0.054 \\Msun ~and M$_2$=0.504$\\pm$0.040 {\\Msun} and radii of R$_1$=27.1$\\pm$0.4 {\\Rsun} and R$_2$=10.4$\\pm$0.2 {\\Rsun}. The pulsating star is almost filling its corresponding Roche lobe wh...

  3. Period and light curve fluctuations of the Kepler Cepheid V1154 Cyg

    CERN Document Server

    Derekas, A; Berdnikov, L; Szabo, R; Smolec, R; Kiss, L L; Szabados, L; Chadid, M; Evans, N R; Kinemuchi, K; Nemec, J M; Seader, S E; Smith, J C; Tenenbaum, P

    2012-01-01

    We present a detailed period analysis of the bright Cepheid-type variable star V1154 Cygni (V =9.1 mag, P~4.9 d) based on almost 600 days of continuous observations by the Kepler space telescope. The data reveal significant cycle-to-cycle fluctuations in the pulsation period, indicating that classical Cepheids may not be as accurate astrophysical clocks as commonly believed: regardless of the specific points used to determine the O-C values, the cycle lengths show a scatter of 0.015-0.02 days over the 120 cycles covered by the observations. A very slight correlation between the individual Fourier parameters and the O-C values was found, suggesting that the O - C variations might be due to the instability of the light curve shape. Random fluctuation tests revealed a linear trend up to a cycle difference 15, but for long term, the period remains around the mean value. We compare the measurements with simulated light curves that were constructed to mimic V1154 Cyg as a perfect pulsator modulated only by the ligh...

  4. The VMC Survey - X. Cepheids, RR Lyrae stars and binaries as probes of the Magellanic System's structure

    CERN Document Server

    Moretti, M I; Muraveva, T; Ripepi, V; Marquette, J B; Cioni, M -R L; Marconi, M; Girardi, L; Rubele, S; Tisserand, P; de Grijs, R; Groenewegen, M A T; Guandalini, R; Ivanov, V D; van Loon, J Th

    2013-01-01

    The VMC survey is obtaining multi-epoch photometry in the Ks band of the Magellanic System down to a limiting magnitude of Ks ~ 19.3 for individual epoch data. The observations are spaced in time such as to provide optimal sampling of the light curves for RR Lyrae stars and for Cepheids with periods up to 20-30 days. We present examples of the Ks-band light curves of Classical Cepheids and RR Lyrae stars we are obtaining from the VMC data and outline the strategy we put in place to measure distances and infer the System three-dimensional geometry from the variable stars. For this purpose the near-infrared Period-Luminosity, Period-Wesenheit, and Period-Luminosity-Colour relations of the system RR Lyrae stars and Cepheids are used. We extensively exploit the catalogues of the Magellanic Clouds' variable stars provided by the EROS-2 and OGLE III/IV microlensing surveys. By combining these surveys we present the currently widest-area view of the Large Magellanic Cloud as captured by the galaxy Cepheids, RR Lyrae...

  5. The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees

    CERN Document Server

    Luck, R Earle

    2011-01-01

    This paper reports on the spectroscopic investigation of 238 Cepheids in the northern sky. Of these stars, about 150 are new to the study of the galactic abundance gradient. These new Cepheids bring the total number of Cepheids involved in abundance distribution studies to over 400. In this work we also consider systematics between various studies and also those which result from the choice of models. We find systematic variations exist at the 0.06 dex level both between studies and model atmospheres. In order to control the systematic effects our final gradients depend only on abundances derived herein. A simple linear fit to the Cepheid data from 398 stars yields a gradient d[Fe/H]/dRG = -0.062 \\pm 0.002 dex/kpc which is in good agreement with previously determined values. We have also reexamined the region of the "metallicity island" of Luck et al. (2006). With the doubling of the sample in that region and our internally consistent abundances, we find there is scant evidence for a distinct island. We also ...

  6. The Cepheid Period-Luminosity Relation at Mid-Infrared Wavelengths: I. First-Epoch LMC Data

    CERN Document Server

    Freedman, Wendy L; Rigby, Jane; Persson, S E; Sturch, Laura

    2008-01-01

    We present the first mid-infrared Period-Luminosity (PL) relations for Large Magellanic Cloud (LMC) Cepheids. Single-epoch observations of 70 Cepheids were extracted from Spitzer IRAC observations at 3.6, 4.5, 5.8 and 8.0 microns, serendipitously obtained during the SAGE (Surveying the Agents of a Galaxy's Evolution) imaging survey of the LMC. All four mid-infrared PL relations have nearly identical slopes over the period range 6 - 88 days, with a small scatter of only +/-0.16 mag independent of period for all four of these wavelengths. We emphasize that differential reddening is not contributing significantly to the observed scatter, given the nearly two orders of magnitude reduced sensitivity of the mid-IR to extinction compared to the optical. Future observations, filling in the light curves for these Cepheids, should noticeably reduce the residual scatter. These attributes alone suggest that mid-infrared PL relations will provide a practical means of significantly improving the accuracy of Cepheid distanc...

  7. Confirmation of previous ground-based Cepheid P-L zero-points using HIPPARCOS trigonometric parallaxes

    Science.gov (United States)

    Sandage, Allan; Tammann, G. A.

    1998-01-01

    Comparisons show agreement at the 0.1-mag level between the calibration of the Cepheid period-luminosity (P-L) relation by Feast and Catchpole (FC) (1997) using the early release of Hipparcos data and four previous ground-based calibrations, three of which are either largely or totally independent of the distance to the LMC. Each of the comparisons has the sense that the FC calibration is brighter, but only at the level of less than about 0.1 mag. In contrast, FC argue that their Hipparcos recalibration leads to a 0.2-mag revision in the distance to the LMC, and thereby to a 10 percent decrease in the Hubble constant. We argue differently. The comparison of the Hipparcos recalibration with others should be made using only local Galactic Cepheids, not based on Cepheids in the LMC that require a set of precepts that are not germane to the direct Hipparcos recalibration. The comparison made here, using only Galactic Cepheids, gives a correction of about 4 percent or less to our value of H0 based on Type Ia supernovae, keeping all other factors and precepts the same.

  8. Extended envelopes around Galactic Cepheids III. Y Oph and alpha Per from near-infrared interferometry with CHARA/FLUOR

    CERN Document Server

    Mérand, A; Kervella, P; Foresto, V Coudé du; Brummelaar, T ten; McAlister, H

    2007-01-01

    Unbiased angular diameter measurements are required for accurate distances to Cepheids using the interferometric Baade Wesselink method (IBWM). The precision of this technique is currently limited by interferometric measurements at the 1.5% level. At this level, the center-to-limb darkening (CLD) and the presence of circumstellar envelopes (CSE) seem to be the two main sources of bias. The observations we performed aim at improving our knowledge of the interferometric visibility profile of Cepheids. In particular, we assess the systematic presence of CSE around Cepheids in order determine accurate distances with the IBWM free from CSE biased angular diameters. We observed a Cepheid (Y Oph) for which the pulsation is well resolved and a non-pulsating yellow supergiant (alpha Per) using long-baseline near-infrared interferometry. We interpreted these data using a simple CSE model we previously developed. We found that our observations of alpha Per do not provide evidence for a CSE. The measured CLD is explained...

  9. Gaia Data Release 1 - The Cepheid & RR Lyrae star pipeline and its application to the south ecliptic pole region

    CERN Document Server

    Clementini, G; Leccia, S; Mowlavi, N; Lecoeur-Taibi, I; Marconi, M; Szabados, L; Eyer, L; Guy, L P; Rimoldini, L; de Fombelle, G Jevardat; Holl, B; Busso, G; Charnas, J; Cuypers, J; De Angeli, F; De Ridder, J; Debosscher, J; Evans, D W; Klagyivik, P; Musella, I; Nienartowicz, K; Ordonez, D; Regibo, S; Riello, M; Sarro, L M; Suveges, M

    2016-01-01

    We present an overview of the Specific Objects Study (SOS) pipeline developed within the Coordination Unit 7 (CU7) of the Gaia Data Processing and Analysis Consortium (DPAC), the coordination unit charged with the processing and analysis of variable sources observed by Gaia, to validate and fully characterise Cepheids and RR Lyrae stars observed by the spacecraft. We describe how the SOS for Cepheids and RR Lyrae stars (SOS Cep&RRL) was specifically tailored to analyse Gaia's G-band photometric time-series with a South Ecliptic Pole (SEP) footprint, which covers an external region of the Large Magellanic Cloud (LMC). G-band time-series photometry and characterization by the SOS Cep&RRL pipeline (mean magnitude and pulsation characteristics) are published in Gaia Data Release 1 (Gaia DR1) for a total sample of 3,194 variable stars, 599 Cepheids and 2,595 RR Lyrae stars, of which 386 (43 Cepheids and 343 RR Lyrae stars) are new discoveries by Gaia. All 3,194 stars are distributed over an area extending ...

  10. On the relative distance of Magellanic Clouds using Cepheid NlR and Optical-NIR PW relations

    CERN Document Server

    Inno, L; Matsunaga, N; Romaniello, M; Primas, F; Buonanno, R; Caputo, F; Genovali, K; Laney, C D; Marconi, M; Pietrinferni, A

    2013-01-01

    We present new estimates of the relative distance of the Magellanic Clouds (MCs) by using NIR and Optical-NIR Cepheid Period Wesenheit (PW) relations. The relative distances are independent of uncertainties affecting the zero-point of the PW relations, but do depend on the adopted pivot periods. We estimated the pivot periods for fundamental (FU) and first overtone (FO) Cepheids on the basis of their period distributions. We found that log P=0.5 (FU) and log P=0.3 (FO) are solid choices, since they trace a main peak and a shoulder in LMC and SMC period distributions. By using the above pivot periods and ten PW relations, we found MC relative distances of 0.53$\\pm$0.06 (FU) and 0.53$\\pm$0.07 (FO) mag. Moreover, we investigated the possibility to use mixed-mode (FU/FO, FO/SO) Cepheids as distance indicators and we found that they follow quite well the PW relations defined by single mode MC Cepheids, with deviations typically smaller than 0.3{\\sigma}.

  11. Structural properties of s-Cepheid velocity curves. Constraining the location of the omega4=2omega1 resonance

    CERN Document Server

    Kienzle-Focacci, M N; Bersier, D F; Pont, F

    1999-01-01

    The light curves of the first overtone classical Cepheids show a discontinuity in their phi_21 vs. P diagram, near P=3.2 days. This feature, commonly attributed to the 2:1 resonance with the fourth overtone, is not reproduced by the hydrodynamical models. With the goal of reexamining the resonance hypothesis, we have obtained new CORAVEL radial velocity curves for 13 s-Cepheids. Together with 11 objects of Krzyt et al.(1998), the combined sample covers the whole range of s-Cepheid periods. The velocity Fourier parameters display a strong characteristic resonant behavior. In striking contrast to photometric ones, they vary smoothly with the pulsation period and show no jump at 3.2 days. The existing radiative hydrodynamical models match the velocity parameters very well. The center of the omega_4 = 2 omega_1 resonance is estimated to occur at P_r = 4.58+-0.04 days, i.e. at a considerable longer period than previously assumed. We identify two new members of the s-Cepheid group: MY Pup and V440 Per.

  12. THREE-DIMENSIONAL MAPS OF THE MAGELLANIC CLOUDS USING RR LYRAE STARS AND CEPHEIDS. II. THE SMALL MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    We use data on variable stars from the Optical Gravitational Lensing Experiment survey to determine the three-dimensional structure of the Small Magellanic Cloud (SMC). Deriving individual distances to RR Lyrae stars and Cepheids, we investigate the distribution of these tracers of the old and young populations in the SMC. Photometrically estimated metallicities are used to determine the distances to 1494 RR Lyrae stars, which have typical ages greater than 9 Gyr. For 2522 Cepheids, with ages of a few tens to a few hundred Myr, distances are calculated using their period-luminosity relation. Individual reddening estimates from the intrinsic color of each star are used to obtain high precision three-dimensional maps. The distances of RR Lyrae stars and Cepheids are in very good agreement with each other. The median distance of the RR Lyrae stars is found to be 61.5 ± 3.4 kpc. For the Cepheids, a median distance of 63.1 ± 3.0 kpc is obtained. Both populations show an extended scale height, with 2.0 ± 0.4 kpc for the RR Lyrae stars and 2.7 ± 0.3 kpc for the Cepheids. This confirms the large depth of the SMC suggested by a number of earlier studies. The young population is very differently oriented than the old stars. While we find an inclination angle of 7° ± 15° and a position angle of 83° ± 21° for the RR Lyrae stars, for the Cepheids an inclination of 74° ± 9° and a position angle of 66° ± 15° is obtained. The RR Lyrae stars show a fairly homogeneous distribution, while the Cepheids roughly follow the distribution of the bar, with their northeastern part being closer to us than the southwestern part of the bar. Interactions between the SMC, Large Magellanic Cloud, and Milky Way are presumably responsible for the tilted, elongated structure of the young population of the SMC.

  13. Radial velocities of southern stars obtained with the photoelectric scanner Coravel. VII. Radial velocity variations of eleven Cepheids in the Large and Small Magellanic clouds

    International Nuclear Information System (INIS)

    We present a second list of systematic radial-velocity measurements of Magellanic-Cloud Cepheids. For five Cepheids in the Large Magellanic Cloud and six in the Small, we give 615 radial-velocity measurements, covering their complete periods. The B magnitudes range from 12.5 to 15.0, and the periods from 42.7 to 134.7 days. All measurements were made with the Coravel photoelectric scanner attached to the Cassegrain focus of the 1.54 m Danish telescope at La Silla, ESO, in Chile, from January 1981 to November 1987. The number of observations for each star varies from 40 to 92. Among the Cepheids, we have identified three long-period spectroscopic binaries. For the remaining Cepheids, radial velocity versus phase diagrams have been fitted by an analytic relation, and the stellar radius variation has been derived by integration of this relation over the whole period

  14. On the effect of rotation on populations of classical Cepheids. II. Pulsation analysis for metallicities 0.014, 0.006, and 0.002

    Science.gov (United States)

    Anderson, R. I.; Saio, H.; Ekström, S.; Georgy, C.; Meynet, G.

    2016-06-01

    Classical Cepheid variable stars (from hereon: Cepheids) are high-sensitivity probes of stellar evolution and fundamental tracers of cosmic distances. While rotational mixing significantly affects the evolution of Cepheid progenitors (intermediate-mass stars), the impact of the resulting changes in stellar structure and composition on Cepheids and their pulsational properties is hitherto unknown. Here we present the first detailed pulsational instability analysis of stellar evolution models that include the effects of rotation, for both fundamental mode and first overtone pulsation. We employ Geneva evolution models spanning a three-dimensional grid in mass (1.7-15 M⊙), metallicity (Z = 0.014, 0.006, 0.002), and rotation (non-rotating, average & fast rotation). We determine (1) hot and cool instability strip (IS) boundaries taking into account the coupling between convection and pulsation; (2) pulsation periods; and (3) rates of period change. We investigate relations between period and (a) luminosity; (b) age; (c) radius; (d) temperature; (e) rate of period change; (f) mass; (g) the flux-weighted gravity-luminosity relation (FWGLR). We confront all predictions aside from those for age with observations, finding generally excellent agreement. We tabulate period-luminosity relations (PLRs) for several photometric pass-bands and investigate how the finite IS width, different IS crossings, metallicity, and rotation affect PLRs. We show that a Wesenheit index based on H, V, and I photometry is expected to have the smallest intrinsic PLR dispersion. We confirm that rotation resolves the Cepheid mass discrepancy. Period-age relations depend significantly on rotation, with rotation leading to older Cepheids, offering a straightforward explanation for evolved stars in binary systems that cannot be matched by conventional isochrones assuming a single age. We further show that Cepheids obey a tight FWGLR. Rotation is a fundamental property of stars that has important

  15. The Secret Lives of Cepheids: The prototype Classical Cepheid δ Cephei is a Pulsed Variable X-ray and FUV Source - Implications for achieving a high precision Hubble Constant (Ho)

    Science.gov (United States)

    Guinan, Edward F.; Engle, Scott G.; Neilson, Hilding; Harper, Graham M.; Remage Evans, Nancy

    2016-06-01

    As part of our “Secret Lives of Cepheids” program, we report that the prototype Classical Cepheid – δ Cep is an X-ray source with pulsation-modulated X-ray & FUV emissions. Recent Chandra X-ray observations, when combined with our previous Chandra & XMM-Newton data, confirm a periodic sharp ~ 5 fold increase in X-ray flux at ~ 0.5φ. The X-ray emission phases with the star's pulsation P = 5.366-d, confirms that the X-ray emissions arise from the Cepheid itself and not from a companion. The X-ray variation is “spike-like” with an Lx (max) ~ 2.1 x1029 erg/s, with plasma temperatures of ~ 2 - 6 MK. The HST-COS FUV fluxes increase ~10-20 times and reach maximum strengths during ~0.88-0.97φ - prior to maximum brightness. The FUV emissions arise from ionized plasmas with T ~10 - 300 x103 K. The FUV emission lines show turbulent broadening near the maximum fluxes. The FUV emissions are best explained by pulsation-induced collisional shocks originating from the star’s pulsating atmosphere. However, the X-ray emissions occur 0.5 - 0.6 φ (~3 days) later than the FUV emission line maxima. Thus, it appears that the X-ray emissions arise further out from the star. We suggests that to produce the observed high temperature X-ray emitting plasmas, that the X-rays most likely arise from pulsation-shock induced turbulent-magnetic heated plasmas. If this behavior is extended to other Cepheids, the presence of pulsation induced X-ray and FUV emissions could play major roles in the dynamics and heating of Cepheid atmospheres and could have consequences affecting the Cepheid Period-Luminosity (P-L) law. For example, the additional energy and shock-heating could produce enhanced mass loss leading to the formation of circumstellar shells. For example, the presence of circumstellar matter could bias the P-L relation if not accounted for. Similar X-ray - UV behavior is indicated by at least one other Cepheid, β Doradus.This research is supported from grants from NASA for the

  16. On the evolutionary and pulsation mass of Classical Cepheids: III. the case of the eclipsing binary Cepheid CEP0227 in the Large Magellanic Cloud

    CERN Document Server

    Moroni, P G Prada; Bono, G; Pietrzynski, G; Gieren, W; Pilecki, B; Graczyk, D; Thompson, I B; .,

    2012-01-01

    We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass, age) of the eclipsing binary system CEP0227 in the LMC. We computed evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were constructed either by neglecting or by including a moderate convective core overshooting (beta=0.2) during central H-burning phases. Models were also constructed either by neglecting or by assuming a canonical (eta=0.4,0.8) or an enhanced (eta=4) mass loss rate. The solutions were computed in three different planes: luminosity-temperature, mass-radius and gravity-temperature. By using the Bayes Factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting (beta=0.2) and a canonical mass loss rate (eta=0.4) give stellar masses for the primary Cepheid M=4.14^{+0.04}_{-0.05} M_su...

  17. The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XIV. Classical and Type II Cepheids in the Galactic Bulge

    CERN Document Server

    Soszynski, I; Pietrukowicz, P; Szymanski, M K; Kubiak, M; Pietrzynski, G; Wyrzykowski, L; Ulaczyk, K; Poleski, R; Kozlowski, S

    2011-01-01

    The fourteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains Cepheid variables detected in the OGLE-II and OGLE-III fields toward the Galactic bulge. The catalog is divided into two main categories: 32 classical Cepheids (21 single-mode fundamental-mode F, four first-overtone 1O, two double-mode F/1O, three double-mode 1O/2O and two triple-mode 1O/2O/3O pulsators) and 335 type II Cepheids (156 BL Her, 128 W Vir and 51 RV Tau stars). Six of the type II Cepheids likely belong to the Sagittarius Dwarf Spheroidal Galaxy. The catalog data include the time-series photometry collected in the course of the OGLE survey, observational parameters of the stars, finding charts, and cross-identifications with the General Catalogue of Variable Stars. We discuss some statistical properties of the sample and compare it with the OGLE catalogs of Cepheids in the Large and Small Magellanic Clouds. Multi-mode classical Cepheids in the Galactic bulge show systematically smaller period ratios than their counter...

  18. The MACHO Project LMC Variable Star Inventory. VIII. The Recent Star Formation History of the Large Magellanic Cloud from the Cepheid Period Distribution

    International Nuclear Information System (INIS)

    We present an analysis of the period distribution of about 1800 Cepheids in the LMC, based on data obtained by the MACHO microlensing experiment and on a previous catalog by C. H. Payne Gaposchkin. Using stellar evolution and pulsation models, we construct theoretical period-frequency distributions that are compared with the observations. These models reveal that a significant burst of star formation has occurred recently in the LMC (∼1.15x108 yr). We also show that during the last ∼108 yr, the main center of star formation has been propagating from southeast to northwest along the bar. We find that the evolutionary masses of Cepheids are still smaller than pulsation masses by ∼7% and that the red edge of the Cepheid instability strip could be slightly bluer than indicated by theory. There are approximately 600 Cepheids with periods below ∼2.5 days that cannot be explained by evolution theory. We suggest that they are anomalous Cepheids and that a number of these stars are double-mode Cepheids. copyright copyright 1999. The American Astronomical Society

  19. The MACHO Project LMC Variable Star Inventory. VIII. The Recent Star Formation History of the Large Magellanic Cloud from the Cepheid Period Distribution

    Energy Technology Data Exchange (ETDEWEB)

    Alcock, C. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Allsman, R.A. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Alves, D.R. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Axelrod, T.S. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Becker, A.C. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Bennett, D.P. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Bersier, D.F. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Cook, K.H. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Freeman, K.C. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Griest, K.; Guern, J.A.; Lehner, M. [Department of Physics, University of California at San Diego, La Jolla, CA 92093 (United States); Marshall, S.L. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Minniti, D. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)]|[Departmento de Astronomia y Astrofisica, Pontificia Universidad Catolica, Casilla 104, Santiago 22 (Chile); Peterson, B.A. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Pratt, M.R. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Quinn, P.J. [European Southern Observatory, D-85748 Garching bei Muenchen (Germany); Rodgers, A.W. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Stubbs, C.W. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); and others

    1999-02-01

    We present an analysis of the period distribution of about 1800 Cepheids in the LMC, based on data obtained by the MACHO microlensing experiment and on a previous catalog by C. H. Payne Gaposchkin. Using stellar evolution and pulsation models, we construct theoretical period-frequency distributions that are compared with the observations. These models reveal that a significant burst of star formation has occurred recently in the LMC ({approximately}1.15thinsp{times}thinsp10{sup 8} yr). We also show that during the last {approximately}10{sup 8} yr, the main center of star formation has been propagating from southeast to northwest along the bar. We find that the evolutionary masses of Cepheids are still smaller than pulsation masses by {approximately}7{percent} and that the red edge of the Cepheid instability strip could be slightly bluer than indicated by theory. There are approximately 600 Cepheids with periods below {approximately}2.5 days that cannot be explained by evolution theory. We suggest that they are anomalous Cepheids and that a number of these stars are double-mode Cepheids. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}

  20. Non-radial pulsation in first overtone Cepheids of the Small Magellanic Cloud

    CERN Document Server

    Smolec, R

    2016-01-01

    We analyse photometry for 138 first overtone Cepheids from the Small Magellanic Cloud, in which Optical Gravitational Lensing Experiment (OGLE) team discovered additional variability with period shorter than first overtone period, and period ratios in the (0.60, 0.65) range. In the Petersen diagram these stars form three well separated sequences. The additional variability cannot correspond to other radial mode. This form of pulsation is still puzzling. We find that amplitude of the additional variability is small, typically 2-4 per cent of the first overtone amplitude, which corresponds to 2-5 mmag. In some stars we find simultaneously two close periodicities corresponding to two sequences in the Petersen diagram. The most important finding is the detection of power excess at half the frequency of the additional variability (at subharmonic) in 35 per cent of the analysed stars. Interestingly, power excess at subharmonic frequency is detected mostly for stars of the middle sequence in the Petersen diagram (74...

  1. 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.

  2. Cepheids and other variable stars and the distance to the Galactic Centre

    Science.gov (United States)

    Matsunaga, Noriyuki

    2013-02-01

    We review and discuss results of our survey of variable stars towards the Galactic Centre and their distances. In our near-infrared monitoring survey using IRSF/SIRIUS, we detected a number of Miras and Cepheids (both classical and type II) within 20 arcmin of the Galactic Centre. These distance indicators yield a distance to the Galactic Centre of between 7.5 and 8.5 kpc. A new calibration of the red clump also leads to a distance of ~ 8 kpc. For these indicators, which are luminosity-based, a large uncertainty resides in the correction for the foreground extinction, which depends on the reddening law. Nevertheless, our estimates are consistent with previous estimates based the kinematics of stars near the Galactic Centre, and this supports the reddening law we use.

  3. Determination of Cepheid parameters by light-curve template-fitting

    CERN Document Server

    Tanvir, N R; Watkins, A; Kanbur, S M; Berdnikov, L N; Ngeow, C C

    2005-01-01

    Determining the parameters (periods, mean magnitudes etc.) of periodic variable stars is a frequently met problem in astronomy. Here we describe techniques to characterise the light-curves of regular variables by applying principal component analysis (PCA) to a training set of high quality data, and to fit the resulting light-curve templates to sparse and noisy photometry. The PCA approach allows us to efficiently represent the multi-band light-curve shapes of each variable, and hence quantitatively describe the average behaviour of the sample as a smoothly varying function of period, and also the range of variation around this average. In this paper we focus particularly on the utility of such methods for analysing HST Cepheid photometry, and present simulations which illustrate the advantages of our PCA template-fitting approach. These are: accurate parameter determination, including light-curve shape information; simultaneous fitting to multiple passbands; quantitative error analysis; objective rejection o...

  4. The VMC Survey. XIX. Classical Cepheids in the Small Magellanic Cloud

    Science.gov (United States)

    Ripepi, V.; Marconi, M.; Moretti, M. I.; Clementini, G.; Cioni, M.-R. L.; de Grijs, R.; Emerson, J. P.; Groenewegen, M. A. T.; Ivanov, V. D.; Piatti, A. E.

    2016-06-01

    The “VISTA near-infrared YJK s survey of the Magellanic Clouds System” (VMC) is collecting deep K s-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, K s light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period–luminosity (PL), period–luminosity–color (PLC), and period–Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involving the V, J, K s bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near–infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V, K s) to estimate the relative SMC–LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of Δμ = 0.55 ± 0.04 mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are μ SMC = 19.01 ± 0.05 mag and μ SMC = 19.04 ± 0.06 mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.

  5. The Shocking Truth about Cepheids: The Secret X-ray Lives of Classical Cepheids: Origin of Pulsed FUV and X-Ray Emissions of delta Cep and beta Dor

    Science.gov (United States)

    Ruby, John; Engle, Scott G.; Guinan, Edward F.

    2016-01-01

    The Cepheid variable stars (delta Cep) and (beta Dor) have shown FUV spectral emission features from hot (10,000- 300,000 K) plasma that correlate with the phasing of their pulsations.(see Engle et al. 2014). These FUV spectral emissions that include NV 1240, OI 1305,C II 1335A, Si IV 1400A, and He II 1640 show peaks prior to the maximum optical brightness (during the "piston" phase of the pulsation that is observed to be in phase with the stellar pulsations, but the observed X-ray emission occurs near minimum light (near 0.4-0.5P) during the maximum radius and coolest phase of the star. Cepheid stars are an integral part of the cosmic distance ladder, due to their Period-Luminosity relationship (the Leavitt Law). Understanding the dynamics of Cepheid stars, especially with respect to FUV and X-ray emissions, is necessary to be confident in assertions derived from the cosmic distance ladder, including establishing the Hubble Constant to more accurate values.Presented here is a possible explanation for the pulsation period-related observed UV and X-ray emissions of these Cepheids. Using stellar interior and atmosphere models, conditions found in the ionization zone and outer atmosphere of these stars may be conducive to shocks being formed that are capable of temperatures great enough to produce x-ray emission. The mechanics of these shocks and their propagation in the atmosphere of the stars can potentially explain both the apparent pulsation-phased peaks for the FUV, as well as the pulsation-phase dependent (currently unexplained) X-ray emissions.This research was supported by NASA Grants: HST grant HST-GO-13019-A, XMM-Newton grant NNX14AAF12G, andChandra Grant GO-15202X. We are very thankful for this support.

  6. The influence of chemical composition on the properties of Cepheid stars I - Period-Luminosity relation vs iron abundance

    CERN Document Server

    Romaniello, M; Mottini, M; Groenewegen, M; Bono, G; François, P

    2004-01-01

    We have assessed the influence of the stellar iron content on the Cepheid Period-Luminosity (PL) relation by relating the V band residuals from the Freedman et al (2001) PL relation to [Fe/H] for 37 Galactic and Magellanic Clouds Cepheids. The iron abundances were measured from FEROS and UVES high-resolution and high-signal to noise optical spectra. Our data indicate that the stars become fainter as metallicity increases, until a plateau or turnover point is reached at about solar metallicity. Our data are incompatible with both no dependence of the PL relation on iron abundance, and with the linearly decreasing behavior often found in the literature (e.g. Kennicutt et al 1998, Sakai et al 2004). On the other hand, non-linear theoretical models of Fiorentino et al (2002) provide a fairly good description of the data.

  7. Optical Identification of Cepheids in 19 Host Galaxies of Type Ia Supernovae and NGC 4258 with the Hubble Space Telescope

    CERN Document Server

    Hoffmann, Samantha L; Riess, Adam G; Yuan, Wenlong; Casertano, Stefano; Filippenko, Alexei V; Tucker, Brad E; Chornock, Ryan; Silverman, Jeffrey M; Welch, Douglas L; Goobar, Ariel; Amanullah, Rahman

    2016-01-01

    We present results of an optical search for Cepheid variable stars using the Hubble Space Telescope (HST) in 19 hosts of Type Ia supernovae (SNe Ia) and the maser-host galaxy NGC 4258, conducted as part of the SH0ES project (Supernovae and H0 for the Equation of State of dark energy). The targets include 9 newly imaged SN Ia hosts using a novel strategy based on a long-pass filter that minimizes the number of HST orbits required to detect and accurately determine Cepheid properties. We carried out a homogeneous reduction and analysis of all observations, including new universal variability searches in all SN Ia hosts, that yielded a total of 2200 variables with well-defined selection criteria -- the largest such sample identified outside the Local Group. These objects are used in a companion paper to determine the local value of H0 with a total uncertainty of 2.4%.

  8. Distances, depth structure, and kinematics of the Magellanic Clouds from disentangling spectra of eclipsing binaries and Cepheids

    Czech Academy of Sciences Publication Activity Database

    Hadrava, Petr; Štefl, S.; Klement, R.; Martayan, C.

    Cambridge Universrity Press: Cambridge, 2013, s. 231-234. (IAU Symposium Proceedings Series. S289). ISBN 9781107033788. ISSN 1743-9213. [Symposium of the International Astronomical Union /289./. Beijing (CN), 27.08.2012-31.08.2012] R&D Projects: GA ČR GA202/09/0772 Institutional support: RVO:67985815 Keywords : binaries * eclipsing * Cepheids Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  9. The Cepheids of NGC 1866: a precise benchmark for the extragalactic distance scale and stellar evolution from modern UBVI photometry

    Science.gov (United States)

    Musella, I.; Marconi, M.; Stetson, P. B.; Raimondo, G.; Brocato, E.; Molinaro, R.; Ripepi, V.; Carini, R.; Coppola, G.; Walker, A. R.; Welch, D. L.

    2016-04-01

    We present the analysis of multiband time series data for a sample of 24 Cepheids in the field of the Large Magellanic Cloud cluster NGC 1866. Very accurate BVI Very Large Telescope photometry is combined with archival UBVI data, covering a large temporal window, to obtain precise mean magnitudes and periods with typical errors of 1-2 per cent and of 1 ppm, respectively. These results represent the first accurate and homogeneous data set for a substantial sample of Cepheid variables belonging to a cluster and hence sharing common distance, age and original chemical composition. Comparisons of the resulting multiband period-luminosity and Wesenheit relations to both empirical and theoretical results for the Large Magellanic Cloud are presented and discussed to derive the distance of the cluster and to constrain the mass-luminosity relation of the Cepheids. The adopted theoretical scenario is also tested by comparison with independent calibrations of the Cepheid Wesenheit zero-point based on trigonometric parallaxes and Baade-Wesselink techniques. Our analysis suggests that a mild overshooting and/or a moderate mass-loss can affect intermediate-mass stellar evolution in this cluster and gives a distance modulus of 18.50 ± 0.01 mag. The obtained V,I colour-magnitude diagram is also analysed and compared with both synthetic models and theoretical isochrones for a range of ages and metallicities and for different efficiencies of core overshooting. As a result, we find that the age of NGC 1866 is about 140 Myr, assuming Z = 0.008 and the mild efficiency of overshooting suggested by the comparison with the pulsation models.

  10. A Database of Cepheid Distance Moduli and TRGB, GCLF, PNLF and SBF Data Useful for Distance Determinations

    OpenAIRE

    Ferrarese, Laura; Ford, Holland C.; Huchra, John,; Kennicutt, Jr., Robert C.; Mould, Jeremy R.; Sakai, Shoko; Freedman, Wendy L.; Peter B. Stetson; Madore, Barry F.; Gibson, Brad K.; Graham, John A.; Hughes, Shaun M.; Illingworth, Garth D.; Kelson, Daniel D.; Macri, Lucas

    1999-01-01

    We present a compilation of Cepheid distance moduli and data for four secondary distance indicators that employ stars in the old stellar populations: the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF), the tip of the red giant branch (TRGB), and the surface brightness fluctuation (SBF) method. The database includes all data published as of July 15, 1999. The main strength of this compilation resides in all data being on a consistent and homogeneou...

  11. Theoretical Models for Classical Cepheids: IV. Mean Magnitudes and Colors and the Evaluation of Distance, Reddening and Metallicity

    OpenAIRE

    F. Caputo(INAF/OAR); Marconi, M.; Ripepi, V.

    1999-01-01

    We discuss the metallicity effect on the theoretical visual and near-infrared PL and PLC relations of classical Cepheids, as based on nonlinear, nonlocal and time--dependent convective pulsating models at varying chemical composition. In view of the two usual methods of averaging (magnitude-weighted and intensity-weighted) observed magnitudes and colors over the full pulsation cycle, we briefly discuss the differences between static and mean quantities. We show that the behavior of the synthe...

  12. VI-Band Follow-Up Observations of Ultra-Long-Period Cepheid Candidates in M31

    CERN Document Server

    Ngeow, Chow-Choong; Yang, Michael Ting-Chang; Lin, Chi-Sheng; Hsiao, Hsiang-Yao; Cheng, Yu-Chi; Lin, Zhong-Yi; Lin, I-Ling; Kanbur, Shashi M; Ip, Wing-Huen

    2015-01-01

    The ultra-long period Cepheids (ULPCs) are classical Cepheids with pulsation periods exceeding $\\approx 80$ days. The intrinsic brightness of ULPCs are ~1 to ~3 mag brighter than their shorter period counterparts. This makes them attractive in future distance scale work to derive distances beyond the limit set by the shorter period Cepheids. We have initiated a program to search for ULPCs in M31, using the single-band data taken from the Palomar Transient Factory, and identified eight possible candidates. In this work, we presented the VI-band follow-up observations of these eight candidates. Based on our VI-band light curves of these candidates and their locations in the color-magnitude diagram and the Period-Wesenheit diagram, we verify two candidates as being truly ULPCs. The six other candidates are most likely other kinds of long-period variables. With the two confirmed M31 ULPCs, we tested the applicability of ULPCs in distance scale work by deriving the distance modulus of M31. It was found to be $\\mu_...

  13. Large Magellanic Cloud Near-Infrared Synoptic Survey. I. Cepheid variables and the calibration of the Leavitt Law

    CERN Document Server

    Macri, Lucas M; Kanbur, Shashi M; Mahzooni, Salma; Smitka, Michael T

    2014-01-01

    We present observational details and first results of a near-infrared (JHKs) synoptic survey of the central region of the Large Magellanic Cloud using the CPAPIR camera at the CTIO 1.5-m telescope. We covered 18 sq. deg. to a depth of Ks~16.5 mag and obtained an average of 16 epochs in each band at any given location. Our catalog contains more than 3.5x10^6 sources, including 1417 Cepheid variables previously studied at optical wavelengths by the OGLE survey. Our sample of fundamental-mode pulsators represents a 9-fold increase in the number of these variables with time-resolved, multi-band near-infrared photometry. We combine our large Cepheid sample and a recent precise determination of the distance to the LMC to derive a robust absolute calibration of the near-infrared Leavitt Law for fundamental-mode and first-overtone Cepheids with 10x better constraints on the slopes relative to previous work. We also obtain calibrations for the Tip of the Red Giant Branch and the Red Clump based on our ensemble photome...

  14. THE MID-INFRARED PERIOD-LUMINOSITY RELATIONS FOR THE SMALL MAGELLANIC CLOUD CEPHEIDS DERIVED FROM SPITZER ARCHIVAL DATA

    International Nuclear Information System (INIS)

    In this paper, we derive the Spitzer IRAC band period-luminosity (P-L) relations for the Small Magellanic Cloud (SMC) Cepheids, by matching the Spitzer archival SAGE-SMC data with the OGLE-III SMC Cepheids. We find that the 3.6 μm and 4.5 μm band P-L relations can be better described using two P-L relations with a break period at log(P) = 0.4: this is consistent with similar results at optical wavelengths for SMC P-L relations. The 5.8 μm and 8.0 μm band P-L relations do not extend to sufficiently short periods to enable a similar detection of a slope change at log(P) = 0.4. The slopes of the SMC P-L relations, for log(P) > 0.4, are consistent with their Large Magellanic Cloud counterparts that were derived from a similar data set. They are also in agreement with those obtained from a small sample of Galactic Cepheids with parallax measurements.

  15. The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VII. Classical Cepheids in the Small Magellanic Cloud

    CERN Document Server

    Soszynski, I; Udalski, A; Szymanski, M K; Kubiak, M; Pietrzynski, G; Wyrzykowski, L; Szewczyk, O; Ulaczyk, K

    2010-01-01

    The seventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS) consists of 4630 classical Cepheids in the Small Magellanic Cloud (SMC). The sample includes 2626 fundamental-mode (F), 1644 first-overtone (1O), 83 second-overtone (2O), 59 double-mode F/1O, 215 double-mode 1O/2O, and 3 triple-mode classical Cepheids. For each object basic parameters, multi-epoch VI photometry collected within 8 or 13 years of observations, and finding charts are provided in the OGLE Internet archive. We present objects of particular interest: exceptionally numerous sample of single-mode second-overtone pulsators, five double Cepheids, two Cepheids with eclipsing variations superimposed on the pulsation light curves. At least 139 first-overtone Cepheids exhibit low-amplitude secondary variations with periods in the range 0.60-0.65 of the primary ones. These stars populate three distinct sequences in the Petersen diagram. The origin of this secondary modulation is still unknown. Contrary to the Large Magellanic Cloud (LMC) ...

  16. ON THE EVOLUTIONARY AND PULSATION MASS OF CLASSICAL CEPHEIDS. III. THE CASE OF THE ECLIPSING BINARY CEPHEID CEP0227 IN THE LARGE MAGELLANIC CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Prada Moroni, P. G. [Dipartimento di Fisica, Universita di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Gennaro, M. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Bono, G. [Dipartimento di Fisica, Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma (Italy); Pietrzynski, G.; Gieren, W.; Pilecki, B.; Graczyk, D. [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Thompson, I. B., E-mail: prada@df.unipi.it [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101-1292 (United States)

    2012-04-20

    We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass and age) of the eclipsing binary system-CEP0227-in the Large Magellanic Cloud (LMC). We computed several sets of evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were also constructed either by neglecting or by including a moderate convective core overshooting ({beta}{sub ov} = 0.2) during central hydrogen-burning phases. Sets of models were also constructed either by neglecting or by assuming a canonical ({eta} = 0.4, 0.8) or an enhanced ({eta} = 4) mass-loss rate. The most probable solutions were computed in three different planes: luminosity-temperature, mass-radius, and gravity-temperature. By using the Bayes factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting ({beta}{sub ov} = 0.2) and a canonical mass-loss rate ({eta} = 0.4) give stellar masses for the primary (Cepheid)-M = 4.14{sup +0.04}{sub -0.05} M{sub Sun }-and for the secondary-M = 4.15{sup +0.04}{sub -0.05} M{sub Sun }-that agree at the 1% level with dynamical measurements. Moreover, we found ages for the two components and for the combined system-t = 151{sup +4}{sub -3} Myr-that agree at the 5% level. The solutions based on evolutionary models that neglect the mass loss attain similar parameters, while those ones based on models that either account for an enhanced mass loss or neglect convective core overshooting have lower Bayes factors and larger confidence intervals. The dependence on the mass-loss rate might be the consequence of the crude approximation we use to mimic this phenomenon. By using the isochrone of the most probable solution and a Gaussian prior on the LMC distance, we found a true distance modulus-18.53{sup +0.02}{sub -0.02} mag-and a reddening value-E(B - V

  17. The VMC Survey. XIII. Type II Cepheids in the Large Magellanic Cloud

    CERN Document Server

    Ripepi, V; Marconi, M; Clementini, G; Cioni, M-R L; de Grijs, R; Emerson, J P; Groenewegen, M A T; Ivanov, V D; Muraveva, T; Piatti, A E; Subramanian, S

    2014-01-01

    The VISTA survey of the Magellanic Clouds System (VMC) is collecting deep $K_\\mathrm{s}$--band time--series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III survey. We present $J$ and $K_\\mathrm{s}$ light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW Vir) and 27 RV Tau variables. We complement our near-infrared photometry with the $V$ magnitudes from the OGLE III survey, allowing us to build a variety of Period-Luminosity ($PL$), Period-Luminosity-Colour ($PLC$) and Period-Wesenheit ($PW$) relationships, including any combination of the $V, J, K_\\mathrm{s}$ filters and valid for BL Her and W Vir classes. These relationships were calibrated in terms of the LMC distanc...

  18. VizieR Online Data Catalog: The VMC survey. XIX. Classical Cepheids in SMC (Ripepi+, 2016)

    Science.gov (United States)

    Ripepi, V.; Marconi, M.; Moretti, M. I.; Clementini, G.; Cioni, M.-R.; de Grijs, R.; Emerson, J. P.; Groenewegen, M. A. T.; Ivanov, V. D.; Piatti, A. E.

    2016-07-01

    In this paper, we present results for the Classical Cepheids (CCs) included in 11 tiles (each tile is 1.5deg2 on the sky) completely or nearly completely observed, processed, and cataloged by the "VISTA near-infrared YJKs survey of the Magellanic Clouds System" (VMC) survey as of 2015 March 9 (including observations obtained until 2014 September). See Figure 1. VMC is a European Southern Observatory (ESO) public survey that is carried out with VIRCAM (VISTA InfraRed Camera) on the ESO/VISTA telescope. The scope of this paper is to present the results for the CCs in the SMC after four years of VMC observations. The SMC is known to host more than 4500 CCs, according to the OGLE III (Soszynski et al. 2010, J/AcA/60/17) and EROS 2 (Tisserand et al. 2007A&A...469..387T; Kim et al. 2014, J/A+A/566/A43) surveys. (2 data files).

  19. The CoRoT discovery of a unique triple-mode cepheid in the galaxy

    CERN Document Server

    Poretti, Ennio; Weiss, Werner W

    2014-01-01

    The exploitation of the CoRoT treasure of stars observed in the exoplanetary field allowed the detection of a unusual triple-mode Cepheid in the Milky Way, CoRoT 0223989566. The two modes with the largest amplitudes and period ratio of 0.80 are identified with the first (P1=1.29 d) and second (P2=1.03 d) radial overtones. The third period, which has the smallest amplitude but able to produce combination terms with the other two, is the longest one (P3=1.89 d). The ratio of 0.68 between the first-overtone period and the third period is the unusual feature. Its identification with the fundamental radial or a nonradial mode is discussed with respect to similar cases in the Magellanic Clouds. In both cases the period triplet and the respective ratios make the star unique in our Galaxy. The distance derived from the period-luminosity relation and the galactic coordinates put CoRoT~0223989566 in the metal-rich environment of the "outer arm" of the Milky Way.

  20. The VMC Survey. XIX. Classical Cepheids in the Small Magellanic Cloud

    CERN Document Server

    Ripepi, V; Moretti, M I; Clementini, G; Cioni, M -R L; de Grijs, R; Emerson, J P; Groenewegen, M A T; Ivanov, V D; Piatti, A E

    2016-01-01

    The VISTA near infrared Y, J, Ks survey of the Magellanic System (VMC) is collecting deep Ks band time series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, Ks light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-wesenheit (PW) relationships, valid for Fundamental (F), First Overtone (FO) and Second Overtone (SO) pulsators. The relations involving V, J, Ks bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V,Ks) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For...

  1. Time Domain Astronomy with the Harvard Plates: from Cepheids to DASCH

    Science.gov (United States)

    Grindlay, Jonathan E.

    2014-06-01

    The ~500,000 Harvard glass plate photographic negatives are the world’s largest and most complete (full sky; 107y time span) database for Time Domain Astronomy (TDA) on days-months-decades to century timescales. With plate fields of view ranging from 3o - 30o exposed quasi-randomly full sky from 1885 - 1992, any object is observed ~1000 - 3000 times, with limiting magnitudes ranging from B =12-18. I briefly review some of the colorful history of this massive plate-taking project and a few of the pivotal discoveries (e.g. the “Leavitt Law” for the Cepheid Period-Luminosity relation) made by visual studies of the plates by the true TDA pioneers, the likely 3C273. The DASCH data are increasingly available 15% now; 100% in 3.5y) for TDA on largely unexplored timescales. We are grateful to NSF for support with grants AST-0407380, AST-0909073 and AST-1313370.

  2. THE CoRoT DISCOVERY OF A UNIQUE TRIPLE-MODE CEPHEID IN THE GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Poretti, E. [INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (Italy); Baglin, A. [LESIA, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, F-92195 Meudon Cedex (France); Weiss, W. W., E-mail: ennio.poretti@brera.inaf.it [Institute of Astronomy, University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria)

    2014-11-10

    The exploitation of the CoRoT treasure of stars observed in the exoplanetary field allowed the detection of a unusual triple-mode Cepheid in the Milky Way, CoRoT 0223989566. The two modes with the largest amplitudes and a period ratio of 0.80 are identified with the first (P {sub 1} = 1.29 days) and second (P {sub 2} = 1.03 days) radial overtones. The third period, which has the smallest amplitude but is able to produce combination terms with the other two, is the longest one (P {sub 3} = 1.89 days). The ratio of 0.68 between the first-overtone period and the third period is the unusual feature. Its identification with the fundamental radial or a nonradial mode is discussed with respect to similar cases in the Magellanic Clouds. In both cases, the period triplet and the respective ratios make the star unique in our Galaxy. The distance derived from the period-luminosity relation and the galactic coordinates put CoRoT 0223989566 in the metal-rich environment of the ''outer arm'' of the Milky Way.

  3. V473 Lyrae, a unique second-overtone Cepheid with two modulation cycles

    CERN Document Server

    Molnár, László

    2014-01-01

    V473 Lyrae is the only Galactic Cepheid with confirmed periodic amplitude and phase variations similar to the Blazhko effect observed in RR Lyrae stars. We collected all available photometric data and some radial velocity measurements to investigate the nature of the modulation. The comparison of the photometric and radial velocity amplitudes confirmed that the star pulsates in the second overtone. The extensive data set, spanning more than 40 years, allowed us to detect a secondary modulation cycle with a period of approximately 5300 days or 14.5 years. The secondary variations can be detected in the period of the primary modulation, as well. Phenomenologically, the light variations are analogous to the Blazhko effect. To find a physical link, we calculated linear hydrodynamic models to search for potential mode resonances that could drive the modulation and found two viable half-integer (n:2) and three n:4 resonances between the second overtone and other modes. If any of these resonances will be confirmed b...

  4. Survey of non-linear hydrodynamic models of type-II Cepheids

    CERN Document Server

    Smolec, R

    2015-01-01

    We present a grid on non-linear convective type-II Cepheid models. The dense model grids are computed for 0.6M_Sun and a range of metallicities ([Fe/H]=-2.0,-1.5,-1.0), and for 0.8M_Sun ([Fe/H]=-1.5). Two sets of convective parameters are considered. The models cover the full temperature extent of the classical instability strip, but are limited in luminosity; for the most luminous models violent pulsation leads to the decoupling of the outermost model shell. Hence, our survey reaches only the shortest period RV Tau domain. In the Hertzsprung-Russel diagram we detect two domains in which period doubled pulsation is possible. The first extends through the BL Her domain and low luminosity W Vir domain (pulsation periods ~2-6.5 d). The second domain extends at higher luminosities (W Vir domain; periods >9.5d). Some models within these domains display period-4 pulsation. We also detect very narrow domains (~10 K wide) in which modulation of pulsation is possible. Another interesting phenomenon we detect is double...

  5. Polaris the Cepheid returns: 4.5 years of monitoring from ground and space

    CERN Document Server

    Bruntt, H; Stello, D; Penny, A J; Eaton, J A; Buzasi, D L; Sasselov, D D; Preston, H L; Miller-Ricci, E

    2008-01-01

    We present the analysis of 4.5 years of nearly continuous observations of the classical Cepheid Polaris, which comprise the most precise data available for this star. We have made spectroscopic measurements from ground and photometric measurements from the WIRE star tracker and the SMEI instrument on the Coriolis satellite. Measurements of the amplitude of the dominant oscillation (P = 4 days), that go back more than a century, show a decrease from 120 mmag to 30 mmag (V magnitude) around the turn of the millennium. It has been speculated that the reason for the decrease in amplitude is the evolution of Polaris towards the edge of the instability strip. However, our new data reveal an increase in the amplitude by about 30% from 2003-2006. It now appears that the amplitude change is cyclic rather than monotonic, and most likely the result of a pulsation phenomenon. In addition, previous radial velocity campaigns have claimed the detection of long-period variation in Polaris (P > 40 days). Our radial velocity d...

  6. Mean angular diameters, distances and pulsation modes of the classical Cepheids FF Aql and T Vul - CHARA/FLUOR near-infrared interferometric observations

    CERN Document Server

    Gallenne, A; Mérand, A; McAlister, H; Brummelaar, T ten; Foresto, V Coudé du; Sturmann, J; Sturmann, L; Turner, N; Farrington, C; Goldfinger, P J

    2012-01-01

    We report the first angular diameter measurements of two classical Cepheids, FF Aql and T Vul, that we have obtained with the FLUOR instrument installed at the CHARA interferometric array. We obtain average limb-darkened angular diameters of \\theta_LD = 0.878 +/- 0.013 mas and \\theta_LD = 0.629 +/- 0.013 mas, respectively for FF Aql and T Vul. Combining these angular diameters with the HST-FGS trigonometric parallaxes leads to linear radii R = 33.6 +/- 2.2 Rsol and R = 35.6 +/- 4.4 Rsol, respectively. The comparison with empirical and theoretical Period-Radius relations leads to the conclusion that these Cepheids are pulsating in their fundamental mode. The knowledge of the pulsation mode is of prime importance to calibrate the Period-Luminosity relation with a uniform sample of fundamental mode Cepheids.

  7. Mean angular diameters, distances, and pulsation modes of the classical Cepheids FF Aquilae and T Vulpeculae. CHARA/FLUOR near-infrared interferometric observations

    Science.gov (United States)

    Gallenne, A.; Kervella, P.; Mérand, A.; McAlister, H.; ten Brummelaar, T.; Coudé du Foresto, V.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J.

    2012-05-01

    We report the first angular diameter measurements of two classical Cepheids, FF Aql and T Vul, that we obtain using observations with the FLUOR instrument installed at the CHARA interferometric array. We derive average limb-darkened angular diameters of θLD = 0.878 ± 0.013 mas and θLD = 0.629 ± 0.013 mas, respectively, for FF Aql and T Vul. Combining these angular diameters with the HST-FGS trigonometric parallaxes leads to linear radii R = 33.6 ± 2.2 R⊙ and R = 35.6 ± 4.4 R⊙, respectively. The comparison with empirical and theoretical period-radius relations leads to the conclusion that these Cepheids are pulsating in their fundamental mode. The knowledge of this pulsation mode is of prime importance to calibrating the period-luminosity relation with a uniform sample of fundamental mode Cepheids.

  8. On the Effect of Rotation on Populations of Classical Cepheids II. Pulsation Analysis for Metallicities 0.014, 0.006, and 0.002

    CERN Document Server

    Anderson, Richard I; Ekström, Sylvia; Georgy, Cyril; Meynet, Georges

    2016-01-01

    Classical Cepheid variable stars are high-sensitivity probes of stellar evolution and fundamental tracers of cosmic distances. While rotational mixing significantly affects the evolution of Cepheid progenitors (intermediate-mass stars), the impact of the resulting changes in stellar structure and composition on Cepheids on their pulsational properties is hitherto unknown. Here we present the first detailed pulsational instability analysis of stellar evolution models that include the effects of rotation, for both fundamental mode and first overtone pulsation. We employ Geneva evolution models spanning a three-dimensional grid in mass (1.7 - 15 $M_\\odot$), metallicity (Z = 0.014, 0.006, 0.002), and rotation (non-rotating, average & fast rotation). We determine (1) hot and cool instability strip (IS) boundaries taking into account the coupling between convection and pulsation, (2) pulsation periods, and (3) rates of period change. We investigate relations between period and (a) luminosity, (b) age, (c) radiu...

  9. Multiplicity of Galactic Cepheids from long-baseline interferometry~III. Sub-percent limits on the relative brightness of a close companion of $\\delta$~Cephei

    CERN Document Server

    Gallenne, A; Kervella, P; Monnier, J D; Schaefer, G H; Roettenbacher, R M; Gieren, W; Pietrzynski, G; McAlister, H; Brummelaar, T ten; Sturmann, J; Sturmann, L; Turner, N; Anderson, R I

    2016-01-01

    We report new CHARA/MIRC interferometric observations of the Cepheid archetype $\\delta$ Cep, which aimed at detecting the newly discovered spectroscopic companion. We reached a maximum dynamic range $\\Delta H $ = 6.4, 5.8, and 5.2 mag, respectively within the relative distance to the Cepheid $r 9.15, 8.31$ and 7.77 mag, respectively for $r < 25$ mas, $25 < r < 50$ mas and $50 < r < 100$ mas. We also found that to be consistent with the predicted orbital period, the companion has to be located at a projected separation $< 24$ mas with a spectral type later than a F0V star.

  10. Statistical Tests for the Metallicity Dependency of the Synthetic Cepheid Period-Luminosity Relations in IRAC Bands

    CERN Document Server

    Ngeow, Chow-Choong; Musella, Ilaria; Cignoni, Michele; Kanbur, Shashi

    2011-01-01

    The mid-infrared (MIR) period-luminosity (P-L) relations for Cepheids will be important in the JWST era, as it holds the promise of deriving the Hubble constant within 2% accuracy. It is expected that the MIR P-L to be insensitive to metallicity. In this work, we test this assumption of metallicity independent of the IRAC band P-L relation by applying well-known statistical methods to the synthetic P-L slopes from a series of pulsating models with known metallicity. The statistical tests suggest that the P-L slopes in MIR are linearly depending on metallicity.

  11. A SEARCH FOR OB ASSOCIATIONS NEAR SOUTHERN LONG-PERIOD CEPHEIDS. V. AQ PUPPIS AND V620 PUPPIS

    International Nuclear Information System (INIS)

    A photometric UBV survey is presented for 610 stars in a region surrounding the Cepheid AQ Puppis and centered southwest of the variable, based upon photoelectric measures for 14 stars and calibrated iris photometry of photographic plates of the field for 596 stars. An analysis of reddening and distance for program stars indicates that the major dust complex in this direction is ∼1.8 kpc distant, producing differential extinction described by a ratio of total-to-selective extinction of R = AV /EB–V = 3.10 ± 0.20. Zero-age main-sequence fitting for the main group of B-type stars along the line of sight yields a distance of 3.21 ± 0.19 kpc (V0 – MV = 12.53 ± 0.13 s.e.). The 29fd97 Cepheid AQ Pup, of field reddening EB–V = 0.47 ± 0.07 (EB–V(B0) = 0.51 ± 0.07), appears to be associated with B-type stars lying within 5' of it as well as with a sparse group of stars, designated Turner 14, centered south of it at J2000.0 = 07:58:37, –29:25:00, with a mean reddening of EB–V = 0.81 ± 0.01. AQ Pup has an inferred luminosity as a cluster member of (MV ) = –5.40 ± 0.25 and an evolutionary age of 3 × 107 yr. Its observed rate of period increase of +300.1 ± 1.2 s yr–1 is an order of magnitude larger than what is observed for Cepheids of comparable period in the third crossing of the instability strip, and may be indicative of a high rate of mass loss or a putative fifth crossing. Another sparse cluster, designated Turner 13, surrounds the newly recognized 2fd59 Cepheid V620 Pup, of space reddening EB–V = 0.64 ± 0.02 (EB–V(B0) = 0.68 ± 0.02), distance 2.88 ± 0.11 kpc (V0 – MV 12.30 ± 0.08 s.e.), evolutionary age 108 yr, and an inferred luminosity as a likely cluster member of (MV) = –2.74 ± 0.11. V620 Pup is tentatively identified as a first crosser, pending additional observations.

  12. Non-radial pulsation in first overtone Cepheids of the Small Magellanic Cloud

    Science.gov (United States)

    Smolec, R.; Śniegowska, M.

    2016-06-01

    We analyse photometry for 138 first overtone Cepheids from the Small Magellanic Cloud, in which Optical Gravitational Lensing Experiment team discovered additional variability with period shorter than first overtone period, and period ratios in the P/P1O ∈ (0.60, 0.65) range. In the Petersen diagram, these stars form three well-separated sequences. The additional variability cannot correspond to other radial mode. This form of pulsation is still puzzling. We find that amplitude of the additional variability is small, typically 2-4 per cent of the first overtone amplitude, which corresponds to 2-5 mmag. In some stars, we find simultaneously two close periodicities corresponding to two sequences in the Petersen diagram. The most important finding is the detection of power excess at half the frequency of the additional variability (at subharmonic) in 35 per cent of the analysed stars. Interestingly, power excess at subharmonic frequency is detected mostly for stars of the middle sequence in the Petersen diagram (74 per cent), incidence rate is much lower for stars of the top sequence (31 per cent), and phenomenon is not detected for stars of the bottom sequence. The amplitude and/or phase of the additional periodicities strongly vary in time. Similar form of pulsation is observed in first overtone RR Lyrae stars. Our results indicate that the nature and cause of this form of pulsation is the same in the two groups of classical pulsators; consequently, a common model explaining this form of pulsation should be searched for. Our results favour the theory of the excitation of non-radial modes of angular degrees 7, 8 and 9, proposed recently by Dziembowski.

  13. Survey of non-linear hydrodynamic models of type-II Cepheids

    Science.gov (United States)

    Smolec, R.

    2016-03-01

    We present a grid of non-linear convective type-II Cepheid models. The dense model grids are computed for 0.6 M⊙ and a range of metallicities ([Fe/H] = -2.0, -1.5, -1.0), and for 0.8 M⊙ ([Fe/H] = -1.5). Two sets of convective parameters are considered. The models cover the full temperature extent of the classical instability strip, but are limited in luminosity; for the most luminous models, violent pulsation leads to the decoupling of the outermost model shell. Hence, our survey reaches only the shortest period RV Tau domain. In the Hertzsprung-Russell diagram, we detect two domains in which period-doubled pulsation is possible. The first extends through the BL Her domain and low-luminosity W Vir domain (pulsation periods ˜2-6.5 d). The second domain extends at higher luminosities (W Vir domain; periods >9.5 d). Some models within these domains display period-4 pulsation. We also detect very narrow domains (˜10 K wide) in which modulation of pulsation is possible. Another interesting phenomenon we detect is double-mode pulsation in the fundamental mode and in the fourth radial overtone. Fourth overtone is a surface mode, trapped in the outer model layers. Single-mode pulsation in the fourth overtone is also possible on the hot side of the classical instability strip. The origin of the above phenomena is discussed. In particular, the role of resonances in driving different pulsation dynamics as well as in shaping the morphology of the radius variation curves is analysed.

  14. The Araucaria Project. The Distance to the Local Group Galaxy IC 1613 from Near-Infrared Photometry of Cepheid Variables

    CERN Document Server

    Pietrzynski, G; Bresolin, F; Dall'Ora, M; Gieren, W; Kudritzki, R P; Soszynski, I; Storm, J

    2006-01-01

    We have measured accurate near-infrared magnitudes in the J and K bands of 39 Cepheid variables in IC 1613 with well-determined periods and optical VI light curves. Using the template light curve approach of Soszy{\\'n}ski, Gieren and Pietrzy{\\'n}ski, accurate mean magnitudes were obtained from these data which allowed to determine the distance to IC 1613 relative to the LMC from a multiwavelength period-luminosity solution in the optical VI and near-IR JK bands, with an unprecedented accuracy. Our result for the IC 1613 distance is $(m-M)_{0} = 24.291 \\pm 0.014$ (random error) mag, with an additional systematic uncertainty smaller than 2%. From our multiwavelength approach, we find for the total (average) reddening to the IC 1613 Cepheids $E(B-V) = 0.090 \\pm 0.007$ mag,which is significantly higher than the foreground reddening of about 0.03 mag,showing the presence of appreciable dust extinction inside the galaxy. Our data suggest that the extinction law in IC 1613 is very similar to the galactic one.Our dis...

  15. Anomalous Cepheids in the Large Magellanic Cloud: Insight on their origin and connection with the star formation history

    CERN Document Server

    Fiorentino, Giuliana

    2012-01-01

    Context: The properties of variable stars can give independent constraints on the star formation history of the host galaxy, through the determination of the age and the metallicity of the parent population. Aims: We investigate the pulsation properties of 84 Anomalous Cepheids (ACs) detected by the OGLE-III survey in the Large Magellanic Cloud (LMC), in order to understand the formation mechanism and the characteristics of the parent population they originated from. Methods: We used updated theoretical pulsation scenario to derive the mass and the pulsation mode of each AC in the sample. We also discuss, by means of a Kolmogorov-Smirnov test, the spatial distribution of the ACs, in comparison with that of other groups of variable stars, and connect their properties with the star formation history of the LMC. Results: We find that the ACs' mean mass is $1.2 \\pm 0.2 M_{\\odot}$. We show that ACs do not follow the same spatial distribution of classical Cepheids. This, and the fact that their period-luminosity re...

  16. The Araucaria Project: A study of the classical Cepheid in the eclipsing binary system OGLE LMC562.05.9009 in the Large Magellanic Cloud

    CERN Document Server

    Gieren, Wolfgang; Pietrzynski, Grzegorz; Graczyk, Dariusz; Udalski, Andrzej; Soszynki, Igor; Thompson, Ian B; Moroni, Pier Giorgio Prada; Smolec, Radoslaw; Konorski, Piotr; Gorski, Marek; Karczmarek, Paulina; Suchomska, Ksenia; Taormina, Monica; Gallenne, Alexandre; Storm, Jesper; Bono, Giuseppe; Catelan, Marcio; Szymanski, Michal; Kozlowski, Szymon; Pietrukowicz, Pawel; Wyrzykowski, Lukasz; Poleski, Radoslaw; Skowron, Jan; Minniti, Dante; Ulaczyk, K; Mroz, P; Pawlak, M; Nardetto, Nicolas

    2015-01-01

    We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigger (M_1 = 3.70 +/- 0.03M_sun, R_1 = 28.6 +/- 0.2R_sun) than its companion (M_2 = 3.60 +/- 0.03M_sun, R_2 = 26.6 +/- 0.2R_sun). Within the observational uncertainties both stars have the same effective temperature of 6030 +/- 150K. Evolutionary tracks place both stars inside the classical Cepheid instability strip, but it is likely that future improved temperature estimates will move the stable giant companion just beyond...

  17. The Extragalactic Distance Scale Key Project VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope

    Science.gov (United States)

    Rawson, D. M.; Mould, J. R.; Macri, L. M.; Huchra, J. P.; Kennicutt, R. C.; Harding, P.; Freedman, W. L.; Hill, R. J.; Phelps, R. L.; Madore, B. F.; Silbermann, N. A.; Graham, J. A.; Ferrarese, L.; Ford, H. C.; Illingworth, G. D.; Hoessel, J. G.; Han, M.; Hughes, S. M.; Saha, A.; Stetson, P. B.

    1996-01-01

    We report on the discovery of Cepheids in the field spiral galaxy NGC3621, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as part of the HST Key Project on the Extragalctic Distance Scale, which aims to measure the Hubble Constant to 10 percent accuracy.

  18. The panchromatic view of the Magellanic Clouds from Classical Cepheids. I. Distance, Reddening and Geometry of the Large Magellanic Cloud disk

    CERN Document Server

    Inno, L; Matsunaga, N; Fiorentino, G; Marconi, M; Lemasle, B; da Silva, R; Soszyński, I; Udalski, A; Romaniello, M; Rix, H -W

    2016-01-01

    We present a detailed investigation of the Large Magellanic Cloud (LMC) disk using classical Cepheids. Our analysis is based on optical (I,V; OGLE-IV), near-infrared (NIR: J,H,Ks) and mid-infrared (MIR: w1; WISE) mean magnitudes. By adopting new templates to estimate the NIR mean magnitudes from single-epoch measurements, we build the currently most accurate, largest and homogeneous multi-band dataset of LMC Cepheids. We determine Cepheid individual distances using optical and NIR Period-Wesenheit relations (PWRs), to measure the geometry of the LMC disk and its viewing angles. Cepheid distances based on optical PWRs are precise at 3%, but accurate to 7, while the ones based on NIR PWRs are more accurate (to 3%), but less precise (2%-15%), given the higher photometric error on the observed magnitudes. We found an inclination i=25.05 $\\pm$ 0.02 (stat.) $\\pm$ 0.55 (syst.) deg, and a position angle of the lines of nodes P.A.=150.76 $\\pm$ 0.02(stat.) $\\pm$ 0.07(syst.) deg. These values agree well with estimates b...

  19. The Araucaria Project: A Study of the Classical Cepheid in the Eclipsing Binary System OGLE LMC562.05.9009 in the Large Magellanic Cloud

    Science.gov (United States)

    Gieren, Wolfgang; Pilecki, Bogumił; Pietrzyński, Grzegorz; Graczyk, Dariusz; Udalski, Andrzej; Soszyński, Igor; Thompson, Ian B.; Prada Moroni, Pier Giorgio; Smolec, Radosław; Konorski, Piotr; Górski, Marek; Karczmarek, Paulina; Suchomska, Ksenia; Taormina, Mónica; Gallenne, Alexandre; Storm, Jesper; Bono, Giuseppe; Catelan, Márcio; Szymański, Michał; Kozłowski, Szymon; Pietrukowicz, Paweł; Wyrzykowski, Łukasz; Poleski, Radosław; Skowron, Jan; Minniti, Dante; Ulaczyk, K.; Mróz, P.; Pawlak, M.; Nardetto, Nicolas

    2015-12-01

    We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius, and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigger (M1 = 3.70 ± 0.03 M⊙, R1 = 28.6 ± 0.2 R⊙) than its companion (M2 = 3.60 ± 0.03 M⊙, R2 = 26.6 ± 0.2 R⊙). Within the observational uncertainties both stars have the same effective temperature of 6030 ± 150 K. Evolutionary tracks place both stars inside the classical Cepheid instability strip, but it is likely that future improved temperature estimates will move the stable giant companion just beyond the red edge of the instability strip. Within current observational and theoretical uncertainties, both stars fit on a 205 Myr isochrone arguing for their common age. From our model, we determine a value of the projection factor of p = 1.37 ± 0.07 for the Cepheid in the OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could measure its p-factor with high precision directly from the analysis of an eclipsing binary system, which represents an important contribution toward a better calibration of Baade-Wesselink methods of distance determination for Cepheids. This research is based on observations obtained with the ESO VLT, 3.6 m and NTT telescopes for Programmes 092.D-0295(A), 091.D-0393(A), 089.D-0330(A), 088.D-0447(A), 086.D-0103(A) and 085.D-0398(A)), and with the Magellan Clay and Warsaw telescopes at Las Campanas Observatory.

  20. A NEW CEPHEID DISTANCE TO THE GIANT SPIRAL M101 BASED ON IMAGE SUBTRACTION OF HUBBLE SPACE TELESCOPE/ADVANCED CAMERA FOR SURVEYS OBSERVATIONS

    International Nuclear Information System (INIS)

    We accurately determine a new Cepheid distance to M101 (NGC 5457) using archival Hubble Space Telescope (HST)/Advanced Camera for Surveys V and I time series photometry of two fields within the galaxy. We make a slight modification to the ISIS image subtraction package to obtain optimal differential light curves from HST data. We discovered 827 Cepheids with periods between 3 and 80 days, the largest extragalactic sample of Cepheids observed with HST by a factor of two. With this large Cepheid sample, we find that the relative distance of M101 from the Large Magellanic Cloud is ΔμLMC = 10.63 ± 0.04 (random) ± 0.06 (systematic) mag. If we use the geometrically determined maser distance to NGC 4258 as our distance anchor, the distance modulus of M101 is μ0 = 29.04 ± 0.05 (random) ± 0.18 (systematic) mag or D = 6.4 ± 0.2 (random) ± 0.5 (systematic) Mpc. The uncertainty is dominated by the maser distance estimate (±0.15 mag), which should improve over the next few years. We determine a steep metallicity dependence, γ, for our Cepheid sample through two methods, yielding γ = -0.80 ± 0.21 (random) ± 0.06 (systematic) mag dex-1 and γ = -0.72+0.22-0.25 (random) ± 0.06 (systematic) mag dex-1. We see marginal evidence for variations in the Wesenheit period-luminosity relation slope as a function of deprojected galactocentric radius. We also use the tip of the red giant branch method to independently determine the distance modulus to M101 of μ0 = 29.05 ± 0.06 (random) ± 0.12 (systematic) mag.

  1. Calibrating the Cepheid Period-Luminosity relation from the infrared surface brightness technique I. The p-factor, the Milky Way relations, and a universal K-band relation

    CERN Document Server

    Storm, J; Fouque, P; Barnes, T G; Pietrzynski, G; Nardetto, N; Weber, M; Granzer, T; Strassmeier, K

    2011-01-01

    We determine Period-Luminosity relations for Milky Way Cepheids in the optical and near-IR bands. These relations can be used directly as reference for extra-galactic distance determination to Cepheid populations with solar metallicity, and they form the basis for a direct comparison with relations obtained in exactly the same manner for stars in the Magellanic Clouds, presented in an accompanying paper. In that paper we show that the metallicity effect is very small and consistent with a null effect, particularly in the near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC and SMC to form a best relation. We employ the near-IR surface brightness (IRSB) method to determine direct distances to the individual Cepheids after we have recalibrated the projection factor using the recent parallax measurements to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC should be independent of pulsation period. We confirm our earlier finding that the projection factor for c...

  2. AMPLITUDE FINE STRUCTURE IN THE CEPHEID P-L RELATION. I. AMPLITUDE DISTRIBUTION ACROSS THE RR LYRAE INSTABILITY STRIP MAPPED USING THE ACCESSIBILITY RESTRICTION IMPOSED BY THE HORIZONTAL BRANCH

    International Nuclear Information System (INIS)

    The largest amplitude light curves for both RR Lyrae (RRL) variables and classical Cepheids with periods less than 10 days and greater than 20 days occur at the blue edge of the respective instability strips. It is shown that the equation for the decrease in amplitude with penetration into the strip from the blue edge, and hence the amplitude fine structure within the strip, is the same for RRL and the Cepheids despite their metallicity differences. However, the manifestation of this identity is different between the two classes of variables because the sampling of the RRL strip is restricted by the discrete strip positions of the horizontal branch, a restriction that is absent for the Cepheids in stellar aggregates with a variety of ages. To show the similarity of the strip amplitude fine structure for RRL and Cepheids, we make a grid of lines of constant amplitude in the H-R diagram of the strip using amplitude data for classical Cepheids in the Galaxy, LMC, and SMC. The model implicit in the grid, that also contains lines of constant period, is used to predict the correlations between period, amplitude, and color for the two Oosterhoff RRL groups in globular clusters. The good agreement of the predictions with the observations using the classical Cepheid amplitude fine structure also for the RRL shows one aspect of the unity of the pulsation processes between the two classes of variables.

  3. H$_{\\alpha}$ line as an indicator of envelope presence around the Cepheid Polaris Aa ($\\alpha~ UMi$)

    CERN Document Server

    Usenko, I A; Klochkova, V G; Tavolzhanskaya, N S

    2015-01-01

    We present the results of the radial velocity ($RV$) measurements of metallic lines as well as H$_{\\alpha}$ (H$_{\\beta}$) obtained in 55 high-resolution spectra of the Cepheid $\\alpha$ UMi (Polaris Aa) in 1994-2010. While the $RV$ amplitudes of these lines are roughly equal, their mean $RV$ begin to differ essentially with growth of the Polaris Aa pulsational activity. This difference is accompanied by the H$_{\\alpha}$ line core asymmetries on the red side mainly (so-called knife-like profiles) and reaches 8-12 km/s in 2003 with a subsequent decrease to 1.5-2 km/s. We interpret a so unusual behaviour of the H$_{\\alpha}$ line core as dynamical changes in the envelope around Polaris Aa.

  4. The Hubble Space Telescope Extragalactic Distance Scale Key Project. 1: The discovery of Cepheids and a new distance to M81

    Science.gov (United States)

    Freedman, Wendy L.; Hughes, Shaun M.; Madore, Barry F.; Mould, Jeremy R.; Lee, Myung Gyoon; Stetson, Peter; Kennicutt, Robert C.; Turner, Anne; Ferrarese, Laura; Ford, Holland

    1994-01-01

    We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I magnitude system using a ground-based calibration. Apparent period-luminosity relations at V and I were constructed, from which apparent distance moduli were measured with respect to assumed values of mu(sub 0) = 18.50 mag and E(B - V) = 0.10 mag for the Large Magellanic Cloud. The difference in the apparent V and I moduli yields a measure of the difference in the total mean extinction between the M81 and the LMC Cepheid samples. A low total mean extinction to the M81 sample of E(B - V) = 0.03 +/- 0.05 mag is obtained. The true distance modulus to M81 is determined to be 27.80 +/- 0.20 mag, corresponding to a distance of 3.63 +/- 0.34 Mpc. These data illustrate that with an optimal (power-law) sampling strategy, the HST provides a powerful tool for the discovery of extragalactic Cepheids and their application to the distance scale. M81 is the first calibrating galaxy in the target sample of the HST Key Project on the Extragalactic Distance Scale, the ultimate aim of which is to provide a value of the Hubble constant to 10% accuracy.

  5. Parallax of Galactic Cepheids from Spatially Scanning the Wide Field Camera 3 on the Hubble Space Telescope: The Case of SS Canis Majoris

    CERN Document Server

    Casertano, Stefano; Anderson, Richard I; Bowers, J Bradley; Clubb, Kelsey I; Cukierman, Aviv R; Filippenko, Alexei V; Graham, Melissa L; MacKenty, John W; Melis, Carl; Tucker, Brad E; Upadhya, Gautam

    2016-01-01

    We present a high-precision measurement of the parallax for the 12-day Cepheid SS Canis Majoris, obtained via spatial scanning with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Spatial scanning enables astrometric measurements with a precision of 20-40 muas, an order of magnitude better than pointed observations. SS CMa is the second Cepheid targeted for parallax measurement with HST, and is the first of a sample of eighteen long-period >~ 10 days) Cepheids selected in order to improve the calibration of their period-luminosity relation and eventually permit a determination of the Hubble constant H_0 to better than 2%. The parallax of SS CMa is found to be 348 +/- 38 muas, corresponding to a distance of 2.9 +/- 0.3 kpc. We also present a refinement of the static geometric distortion of WFC3 obtained using spatial scanning observations of calibration fields, with a typical magnitude <~0.01 pixels on scales of 100 pixels.

  6. The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. I. Classical Cepheids in the Large Magellanic Cloud

    CERN Document Server

    Soszynski, I; Udalski, A; Szymanski, M K; Kubiak, M; Pietrzynski, G; Wyrzykowski, L; Szewczyk, O; Ulaczyk, K

    2008-01-01

    We present the first part of a new catalog of variable stars (OIII-CVS) compiled from the data collected in the course of the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). In this paper we describe the catalog of 3361 classical Cepheids detected in the ~40 square degrees area in the Large Magellanic Cloud. The sample consists of 1848 fundamental-mode (F), 1228 first-overtone (1O), 14 second-overtone (2O), 61 double-mode F/1O, 203 double-mode 1O/2O, 2 double-mode 1O/3O, and 5 triple-mode classical Cepheids. This sample is supplemented by the list of 23 ultra-low amplitude variable stars which may be Cepheids entering or exiting instability strip. The catalog data include VI high-quality photometry collected since 2001, and for some of the stars supplemented by OGLE-II photometry obtained between 1997 and 2000. We provide basic parameters of the stars: coordinates, periods, mean magnitudes, amplitudes and parameters of the Fourier light curves decompositions. Individual objects of part...

  7. Discovery of Cepheids in NGC 5253: Absolute peak brightness of SN Ia 1895B and SN Ia 1972E and the value of H(sub 0)

    Science.gov (United States)

    Saha, A.; Sandage, Allan; Labhardt, Lukas; Schwengeler, Hans; Tammann, G. A.; Panagia, N.; Macchetto, F. D.

    1995-01-01

    Observations of the Hubble Space Telescope (HST) between 1993 May 31 and 1993 July 19 in 20 epochs in the F555W passband and five epochs in the F785LP passband have led to the discovery of 14 Cepheids in the Amorphous galaxy NGC 5253. The apparent V distance modulus is (m-M)(sub AV) = 28.08 +/- 0.10 determined from the 12 Cepheids with normal amplitudes. The distance modulus using the F785LP data is consistent with the V value to within the errors. Five methods used to determine the internal reddening are consistent with zero differential reddening, accurate to a level of E(B-V) less than 0.05 mag, over the region occupied by Cepheids and the two supernovae (SNe) produced by NGC 5253. The apparent magnitudes at maximum for the two SNe in NGC 5253 are adopted as B(sub max) = 8.33 +/- 0.2 mag for SN 1895B, and B(sub max) = 8.56 +/- 0.1 and V(sub max) = 8.60 +/- 0.1 for SN 1972E which is a prototype SN of Type Ia. The apparent magnitude system used by Walker (1923) for SN 1859B has been corrected to the modern B scale and zero point to determine its adopted B(sub max) value.

  8. The MACHO Project LMC Variable Star Inventory. VII. The Discovery of RV Tauri Stars and New Type II Cepheids in the Large Magellanic Cloud

    Energy Technology Data Exchange (ETDEWEB)

    Alcock, C. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)]|[Center for Particle Astrophysics, University of California, Berkeley, Berkeley, California 94720 (United States); Allsman, R.A. [Supercomputing Facility, Australian National University, Canberra, ACT 0200 (Australia); Alves, D.R. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)]|[Department of Physics, University of California, Davis, Davis, California 95616 (United States); Axelrod, T.S. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Becker, A. [Center for Particle Astrophysics, University of California, Berkeley, Berkeley, California 94720 (United States)]|[Department of Astronomy and Physics, University of Washington, Seattle, Washington 98195 (United States); Bennett, D.P. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)]|[Center for Particle Astrophysics, University of California, Berkeley, Berkeley, California 94720 (United States)]|[Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Cook, K.H. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)]|[Center for Particle Astrophysics, University of California, Berkeley, Berkeley, California 94720 (United States); Freeman, K.C. [Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611 (Australia); Griest, K. [Center for Particle Astrophysics, University of California, Berkeley, Berkeley, California 94720 (United States)]|[Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Lawson, W.A. [Department of Physics, Australian Defence Force Academy, University of New South Wales, Canberra, ACT 2600 (Australia); Lehner, M.J. [Center for Particle Astrophysics, University of California, Berkeley, Berkeley (United States)

    1998-05-01

    We report the discovery of RV Tauri stars in the Large Magellanic Cloud (LMC). In light- and color-curve behavior, the RV Tauri stars appear to be a direct extension of the type II Cepheids to longer periods. A single period-luminosity-color relationship is seen to describe both the type II Cepheids and the RV Tauri stars in the LMC. We derive the relation {ital V}{sub 0} = 17.89({plus_minus}0.20){minus}2.95({plus_minus}0.12) log {ital P} + 5.49({plus_minus}0.35){l_angle}({ital V} {minus} {ital R}){sub 0}{r_angle}, which is valid for type II Cepheids and RV Tauri stars in the period range 0.9 {lt} log {ital P} {lt} 1.75. Assuming a distance modulus to the LMC of 18.5, the relation in terms of the absolute luminosities becomes {ital M}{sub {ital V}} = {minus}0.61({plus_minus}0.20){minus}2.95({plus_minus}0.12) log {ital P} + 5.49({plus_minus}0.35){l_angle}({ital V} {minus} {ital R}){sub 0}{r_angle}. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}

  9. Spectroscopic studies of the classical Cepheid ζ Gem: Analysis of the velocity field in the atmosphere and manifestation of the presence of a circumstellar envelope

    Science.gov (United States)

    Usenko, I. A.

    2016-06-01

    Based on five high-resolution spectra in the range 5625-7525 ˚A taken in 1995 and covering the ascending branch of the light curve from minimum to maximum, we have performed spectroscopic studies of the classical Cepheid ζ Gem. The atmospheric parameters and chemical composition of the Cepheid have been refined. The abundances of the key elements of the evolution of yellow supergiants are typical for an object that has passed the first dredge-up: a C underabundance, N, Na, and Al overabundances, and nearly solar O and Mg abundances. We have estimated [Fe/H] = +0.01 dex; the abundances of the remaining elements are also nearly solar. The metal absorption lines in all spectra show a clear asymmetry and the formation of secondary blue (B1 and B2) and red (R1 and R2) components, just as for the Cepheid X Sgr. The Hα absorption line is also split into blue (B) and red (R) components with different depths changing with pulsation phase. To analyze the velocity field in the atmosphere of ζ Gem, we have estimated the radial velocities from specially selected (with clear signatures of the B1, B2, R1, and R2 components) absorption lines (neutral atoms and ions) of metals (38 lines) and the B and R components of the Hα line. Analysis of these estimates has shown that their scatter is from -22 to 36 km s-1 for all pulsation phases but does not exceed 35-40 km s-1 for each individual phase, while it does not exceed 22 km s-1 for the Hα line components. The radial velocity estimates for the metal lines and their B1 and B2 components have been found to depend on the depths, suggesting the presence of a velocity gradient in the atmosphere. No significant difference in velocities between the atoms and ions of the metal lines is observed, i.e., there is no significant inhomogeneity in the upper atmospheric layers of the Cepheid. Since the averaged radial velocity estimates for the cores of the metal lines and their B1 and B2 components change with pulsation phase and coincide

  10. Multisite Evaluation of Cepheid Xpert Carba-R Assay for Detection of Carbapenemase-Producing Organisms in Rectal Swabs.

    Science.gov (United States)

    Tato, M; Ruiz-Garbajosa, P; Traczewski, M; Dodgson, A; McEwan, A; Humphries, R; Hindler, J; Veltman, J; Wang, H; Cantón, R

    2016-07-01

    Rapid identification of patients who are colonized with carbapenemase-producing organisms (CPO) is included in multiple national guidelines for containment of these organisms. In a multisite study, we evaluated the performance of the Cepheid Xpert Carba-R assay, a qualitative diagnostic test that was designed for the rapid detection and differentiation of the blaKPC, blaNDM, blaVIM, blaOXA-48, and blaIMP-1 genes from rectal swab specimens. A double rectal swab set was collected from 383 patients admitted at four institutions (2 in the United States, 1 in the United Kingdom, 1 in Spain). One swab was used for reference culture (MacConkey broth containing 1 mg/liter of meropenem and subcultured to a MacConkey agar plate with a 10-μg meropenem disk) and for sequencing of DNA obtained from carbapenem-nonsusceptible isolates for carbapenemase identification. The other swab was used for the Xpert Carba-R assay. In addition to the clinical rectal swabs, 250 contrived specimens (108 well-characterized CPO and 142 negative controls spiked onto negative rectal swabs) were tested. Overall, 149/633 (23.5%) samples were positive by the Xpert Carba-R assay. In 6 samples, multiple targets were detected (4 VIM/OXA-48, 1 IMP-1/NDM, and 1 NDM/KPC). The Xpert Carba-R assay detected 155 targets (26 IMP-1, 30 VIM, 27 NDM, 33 KPC, 39 OXA-48) within a time range of 32 to 48 min. The sensitivity, specificity, and positive and negative predictive values of the Xpert Carba-R assay compared to those of the reference culture and sequencing results were 96.6% (95% confidence interval [CI], 92.2% to 98.9%), 98.6% (95% CI, 97.1% to 99.4%), 95.3%, and 99.0%, respectively. The Cepheid Xpert Carba-R assay is an accurate and rapid test to identify rectal colonization with CPO, which can guide infection control programs to limit the spread of these organisms. PMID:27122379

  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. C, N, O, and Na Abundances of Cepheid Variables: Implications on the Mixing Process in the Envelope

    CERN Document Server

    Takeda, Y; Han, I; Lee, B -C; Kim, K -M

    2013-01-01

    With an aim of investigating the nature of evolution-induced mixing in the envelope of evolved intermediate-mass stars, we carried out an extensive spectroscopic study for 12 Cepheid variables of various pulsation periods (~2-16 days) to determine the photospheric abundances of C, N, O, and Na, which are the key elements for investigating how the H-burning products are salvaged from the interior, based on 122 high-dispersion echelle spectra (~10 per target) of wide wavelength coverage collected at Bohyunsan Astronomical Observatory. Having established the relevant atmospheric parameters corresponding to each phase spectroscopically from the equivalent widths of Fe I and Fe II lines, we derived C, N, O, and Na abundances from C I, O I, N I, and Na I lines by using the spectrum-synthesis fitting technique, while taking into account the non-LTE effect. The resulting abundances of these elements for 12 program stars turned out to show remarkably small star-to-star dispersions (<~0.1-0.2dex) without any signifi...

  13. Search for evolutionary changes in Cepheid periods using the Harvard plate collection: ASAS 101538-5933.1

    Science.gov (United States)

    Berdnikov, L. N.

    2010-08-01

    In the plate collection of the Harvard College Observatory, we have obtained 528 photographic magnitude estimates for the recently discovered long-period classical Cepheid ASAS 101538-5933.1 ( P = 51.4 days). Together with the published photoelectric and CCD observations, our data have allowed us to construct an O-C diagram spanning a time interval of 120 years. The O-C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period, dP/dt = 51.8 (±4.8) s yr-1 or dot P / P = 7.3 (±0.7) s, in agreement with the results of theoretical calculations for the third crossing of the instability strip. The available data reduced by the method of Eddington and Plakidis reveal small random period fluctuations that do not distort the evolutionary trend in the O-C residuals.

  14. Discovery of Cycle-to-cycle Modulated Spectral Line Variability and Velocity Gradients in Long-period Cepheids

    CERN Document Server

    Anderson, Richard I

    2016-01-01

    This work reports the discovery of cycle-to-cycle modulated spectral line and atmospheric velocity gradient variability in long-period Cepheids based on 925 high-resolution optical spectra of $\\ell$ Carinae (P $\\sim$ 35.5 d) recorded during three heavy duty-cycle monitoring campaigns (in 2014, 2015, and 2016). Spectral line variability is investigated via cross-correlation functions (CCFs) computed using three sets of spectral lines (weak, solar, strong). A metallic line velocity gradient, {\\delta}v$_r$ (t), is computed as the difference between weak and strong-line RVs. CCF shape indicators BIS (asymmetry), FWHM, and depth all exhibit clear phase-dependent variability patterns that differ from one pulsation cycle to the next. Weak-line CCFs exhibit these effects more clearly than strong-line CCFs. BIS exhibits the most peculiar modulated variability and can be used to identify the presence of cycle-to-cycle modulated line profile variations. {\\delta}v$_r$ (t) clearly exhibits cycle-to-cycle differences that ...

  15. Evaluation of the Cepheid Xpert Flu Assay for Rapid Identification and Differentiation of Influenza A, Influenza A 2009 H1N1, and Influenza B Viruses

    OpenAIRE

    Novak-Weekley, S. M.; Marlowe, E. M.; Poulter, M.; Dwyer, D.; Speers, D; Rawlinson, W; Baleriola, C.; Robinson, C C

    2012-01-01

    The Xpert Flu Assay cartridge is a next-generation nucleic acid amplification system that provides multiplexed PCR detection of the influenza A, influenza A 2009 H1N1, and influenza B viruses in approximately 70 min with minimal hands-on time. Six laboratories participated in a clinical trial comparing the results of the new Cepheid Xpert Flu Assay to those of culture or real-time PCR with archived and prospectively collected nasal aspirate-wash (NA-W) specimens and nasopharyngeal (NP) swabs ...

  16. The Eclipsing Binary Cepheid OGLE-LMC-CEP-0227 in the Large Magellanic Cloud: pulsation modelling of light and radial velocity curves

    CERN Document Server

    Marconi, M; Bono, G; Pietrzynski, G; Gieren, W; Pilecki, B; Stellingwerf, R F; Graczyk, D; Smolec, R; Konorski, P; Suchomska, K; Gorski, M; Karczmarek, P

    2013-01-01

    We performed a new and accurate fit of light and radial velocity curves of the Large Magellanic Cloud (LMC) Cepheid --OGLE-LMC-CEP-0227-- belonging to a detached double-lined eclipsing binary system. We computed several sets of nonlinear, convective models covering a broad range in stellar mass, effective temperature and in chemical composition. The comparison between theory and observations indicates that current theoretical framework accounts for luminosity --V and I band-- and radial velocity variations over the entire pulsation cycle. Predicted pulsation mass --M=4.14+-0.06 Mo-- and mean effective temperature --Te=6100+-50 K-- do agree with observed estimates with an accuracy better than 1 sigma. The same outcome applies, on average, to the luminosity amplitudes and to the mean radius. We find that the best fit solution requires a chemical composition that is more metal--poor than typical LMC Cepheids (Z=0.004 vs 0.008) and slightly helium enhanced (Y=0.27 vs 0.25), but the sensitivity to He abundance is ...

  17. Vetting Galactic Leavitt Law Calibrators using Radial Velocities: On the Variability, Binarity, and Possible Parallax Error of 19 Long-period Cepheids

    CERN Document Server

    Anderson, R I; Riess, A G; Melis, C; Holl, B; Semaan, T; Papics, P I; Blanco-Cuaresma, S; Eyer, L; Mowlavi, N; Palaversa, L; Roelens, M

    2016-01-01

    We investigate the radial velocity (RV) variability and spectroscopic binarity of 19 Galactic long-period ($P_{\\rm{puls}} \\gtrsim 10$ d) classical Cepheid variable stars whose trigonometric parallaxes are being measured using the Hubble Space Telescope and Gaia. Our primary objective is to constrain possible parallax error due to undetected orbital motion. Using $>1600$ high-precision RVs measured between 2011 and 2016, we find no indication of orbital motion on $\\lesssim 5$ yr timescales for 18 Cepheids and determine upper limits on allowed configurations for a range of input orbital periods. The results constrain the unsigned parallax error due to orbital motion to $ 10$ yr) variations in pulsation-averaged velocity $v_\\gamma$ via a template fitting approach using both new and literature RVs. We discover the spectroscopic binarity of XZ Car and CD Cyg, find first tentative evidence for AQ Car, and reveal KN Cen's orbital signature. Further (mostly tentative) evidence of time-variable $v_\\gamma$ is found for...

  18. On the Variation of Fourier Parameters for Galactic and LMC Cepheids at Optical, Near-Infrared and Mid-Infrared Wavelengths

    CERN Document Server

    Bhardwaj, Anupam; Singh, Harinder P; Macri, Lucas M; Ngeow, Chow-Choong

    2014-01-01

    We present a light curve analysis of fundamental-mode Galactic and Large Magellanic Cloud (LMC) Cepheids based on the Fourier decomposition technique. We have compiled light curve data for Galactic and LMC Cepheids in optical ({\\it VI}), near-infrared ({\\it JHK}$_s$) and mid-infrared (3.6 $\\&$ 4.5-$\\mu$m) bands from the literature and determined the variation of their Fourier parameters as a function of period and wavelength. We observed a decrease in Fourier amplitude parameters and an increase in Fourier phase parameters with increasing wavelengths at a given period. We also found a decrease in the skewness and acuteness parameters as a function of wavelength at a fixed period. We applied a binning method to analyze the progression of the mean Fourier parameters with period and wavelength. We found that for periods longer than about 20 days, the values of the Fourier amplitude parameters increase sharply for shorter wavelengths as compared to wavelengths longer than the $J$-band. We observed the variati...

  19. The HST Key Project on the Extragalactic Distance Scale XXV A Recalibration of Cepheid Distances to Type Ia Supernovae and the Value of the Hubble Constant

    CERN Document Server

    Gibson, B K; Freedman, W L; Mould, J R; Kennicutt, R C; Huchra, J P; Sakai, S; Graham, J A; Fassett, C I; Kelson, D D; Ferrarese, L; Hughes, S M G; Illingworth, G D; Macri, L M; Madore, B F; Sebo, K M; Silbermann, N A; Gibson, Brad K.; Stetson, Peter B.; Freedman, Wendy L.; Mould, Jeremy R.; Kennicutt, Robert C.; Huchra, John P.; Sakai, Shoko; Graham, John A.; Fassett, Caleb I.; Kelson, Daniel D.; Ferrarese, Laura; Hughes, Shaun M.G.; Illingworth, Garth D.; Macri, Lucas M.; Madore, Barry F.; Sebo, Kim M.; Silbermann, Nancy A.

    1999-01-01

    Cepheid-based distances to seven Type Ia supernovae (SNe)-host galaxies have been derived using the standard HST Key Project on the Extragalactic Distance Scale pipeline. For the first time, this allows for a transparent comparison of data accumulated as part of three different HST projects, the Key Project, the Sandage et al. Type Ia SNe program, and the Tanvir et al. Leo I Group study. Re-analyzing the Tanvir et al. galaxy and six Sandage et al. galaxies we find a mean (weighted) offset in true distance moduli of 0.12+/-0.07 mag -- i.e., 6% in linear distance -- in the sense of reducing the distance scale, or increasing H0. Adopting the reddening-corrected Hubble relations of Suntzeff et al. (1999), tied to a zero point based upon SNe~1990N, 1981B, 1998bu, 1989B, 1972E and 1960F and the photometric calibration of Hill et al. (1998), leads to a Hubble constant of H0=68+/-2(random)+/-5(systematic) km/s/Mpc. Adopting the Kennicutt et al. (1998) Cepheid period-luminosity-metallicity dependency decreases the inf...

  20. Evaluation of the Cepheid Xpert Flu Assay for rapid identification and differentiation of influenza A, influenza A 2009 H1N1, and influenza B viruses.

    Science.gov (United States)

    Novak-Weekley, S M; Marlowe, E M; Poulter, M; Dwyer, D; Speers, D; Rawlinson, W; Baleriola, C; Robinson, C C

    2012-05-01

    The Xpert Flu Assay cartridge is a next-generation nucleic acid amplification system that provides multiplexed PCR detection of the influenza A, influenza A 2009 H1N1, and influenza B viruses in approximately 70 min with minimal hands-on time. Six laboratories participated in a clinical trial comparing the results of the new Cepheid Xpert Flu Assay to those of culture or real-time PCR with archived and prospectively collected nasal aspirate-wash (NA-W) specimens and nasopharyngeal (NP) swabs from children and adults. Discrepant results were resolved by DNA sequence analysis. After discrepant-result analysis, the sensitivities of the Xpert Flu Assay for prospective NA-W specimens containing the influenza A, influenza A 2009 H1N1, and influenza B viruses compared to those of culture were 90.0%, 100%, and 100%, respectively, while the sensitivities of the assay for prospective NP swabs compared to those of culture were 100%, 100%, and 100%, respectively. The sensitivities of the Xpert Flu Assay for archived NA-W specimens compared to those of Gen-Probe ProFlu+ PCR for the influenza A, influenza A 2009 H1N1, and influenza B viruses were 99.4%, 98.4%, and 100%, respectively, while the sensitivities of the Xpert Flu Assay for archived NP swabs compared to those of ProFlu+ were 98.1%, 100%, and 93.8%, respectively. The sensitivities of the Xpert Flu Assay with archived NP specimens compared to those of culture for the three targets were 97.5%, 100%, and 93.8%, respectively. We conclude that the Cepheid Xpert Flu Assay is an accurate and rapid method that is suitable for on-demand testing for influenza viral infection. PMID:22378908

  1. New period-luminosity and period-color relations of classical Cepheids. IV. The low-metallicity galaxies IC 1613, WLM, Pegasus, Sextans A and B, and Leo A in comparison to SMC

    CERN Document Server

    Tammann, G A; Sandage, A

    2010-01-01

    The metal-poor Cepheids in the dwarf galaxies IC 1613, WLM, Pegasus, Sextans A and B, and Leo A are compared with the about equally metal-poor Cepheids of SMC. The period-color (P-C) and period-luminosity (P-L) relations - extended to the shortest periods and for overtone pulsators - of the six galaxies are undistinguishable, but are distinctly different from those in LMC and the solar neighborhood. Adopting (m-M)^{0}_{SMC}=18.93 from independent evidence, one can determine reliable distance moduli for the other dwarf galaxies: (m-M)^{0} = 24.36+/-0.02, 24.81+/-0.04, 24.86+/-0.06, 25.62+/-0.04, and 24.63+/-0.04, respectively. They are in good agreement with independent moduli from RR Lyrae stars and the tip of the red-giant branch (TRGB).

  2. Cepheid Distances to SNe Ia Host Galaxies based on a Revised Photometric Zero-Point of the HST-WFPC2 and New P-L Relations and Metallicity Corrections

    OpenAIRE

    Saha, A.; Thim, F.; Tammann, G. A.; Reindl, B.; Sandage, A.

    2006-01-01

    With this paper we continue the preparation for a forthcoming summary report of our experiment with the Hubble Space Telescope (HST) to determine the Hubble constant using type Ia supernovae as standard candles. Two problems are addressed. (1) We examine the need for, and determine the value of, the corrections to the apparent magnitudes of our program Cepheids in the eleven previous calibration papers due to sensitivity drifts and charge transfer effects of the HST WFPC2 camera over the life...

  3. The Carnegie Chicago Hubble Program: The Mid-Infrared Colours of Cepheids and the Effect of Metallicity on the CO Band-head at $4.6\\mu$m

    CERN Document Server

    Scowcroft, Victoria; Freedman, Wendy L; Beaton, Rachael L; Madore, Barry F; Rich, Andrew J Monson Jeffrey A; Rigby, Jane R

    2016-01-01

    We compare mid-infrared 3.6 and 4.5 $\\mu$m Warm Spitzer observations for Cepheids in the Milky Way and the Large and Small Magellanic Clouds. Using models, we explore in detail the effect of the CO rotation-vibration band-head at 4.6 $\\mu$m on the mid-infrared photometry. We confirm the temperature sensitivity of the CO band-head at 4.6 $\\mu$m and find no evidence for an effect at 3.6 $\\mu$m. We compare the ([3.6]-[4.5]) period-colour relations in the MW, LMC, and SMC. The slopes of the period-colour relations for the three galaxies are in good agreement, but there is a trend in zero-point with metallicity, with the lowest metallicity Cepheids having redder mid-IR colours. Finally, we present a colour-[Fe/H] relation based on published spectroscopic metallicities. This empirical relation, calibrated to the metallicity system of Genovali et al. (2014), demonstrates that the ([3.6]-[4.5]) colour provides a reliable metallicity indicator for Cepheids, with a precision comparable to current spectroscopic determin...

  4. Evaluation of the Cepheid Xpert Clostridium difficile Epi assay for diagnosis of Clostridium difficile infection and typing of the NAP1 strain at a cancer hospital.

    Science.gov (United States)

    Babady, N Esther; Stiles, Jeffrey; Ruggiero, Phyllis; Khosa, Perminder; Huang, David; Shuptar, Susan; Kamboj, Mini; Kiehn, Timothy E

    2010-12-01

    Clostridium difficile is the most common cause of health care-associated diarrhea. Accurate and rapid diagnosis is essential to improve patient outcome and prevent disease spread. We compared our two-step diagnostic algorithm, an enzyme immunoassay for glutamate dehydrogenase (GDH) followed by the cytotoxin neutralization test (CYT) with a turnaround time of 24 to 48 h, versus the Cepheid Xpert C. difficile Epi assay, a PCR-based assay with a turnaround time of tcdC gene and PCR ribotyping. In phase 1, the agreement between the GDH-CYT and the GDH-Xpert PCR was 72%. The sensitivities and specificities of GDH-CYT and GDH-Xpert PCR were 57% and 97% and 100% and 97%, respectively. In phase 2, the agreement between GDH-CYT and Xpert PCR alone was 95%. As in phase 1, sensitivity of the Xpert PCR was higher than that of the GDH-CYT. The correlation between PCR-ribotyping, sequencing, and Xpert PCR for detection of NAP1 strains was excellent (>90%). The excellent sensitivity and specificity and the rapid turnaround time of the Xpert PCR assay as well as its strain-typing capability make it an attractive option for diagnosis of C. difficile infection. PMID:20943860

  5. Performance of Cepheid® Xpert MTB/RIF® and TB Biochip® MDR in two regions of Russia with a high prevalence of drug-resistant tuberculosis

    Science.gov (United States)

    Kurbatova, Ekaterina V.; Kaminski, Dorothy A.; Erokhin, Vladislav V.; Volchenkov, Grigory V.; Andreevskaya, Sofia N.; Chernousova, Larisa N.; Demikhova, Olga V.; Ershova, Julia V.; Kaunetis, Natalia V.; Kuznetsova, Tatiana A.; Larionova, Elena E.; Smirnova, Tatiana G.; Somova, Tatiana R.; Vasilieva, Irina A.; Vorobieva, Alena V.; Zolkina, Svetlana S.; Cegielski, J. Peter

    2015-01-01

    Purpose To assess the performance of Cepheid® Xpert MTB/RIF® (“Xpert”) and TB Biochip® MDR (“TB-Biochip”). Methods Sputum specimens from adults with presumptive tuberculosis (TB) were homogenized and split for (1) direct Xpert and microscopy, and (2) concentration for Xpert, microscopy, culture (Lowenstein-Jensen [LJ] solid media and Mycobacteria Growth Indicator Tube® [MGIT]), indirect drug susceptibility testing (DST) using the absolute concentration method and MGIT, and TB-Biochip. Results In total, 109 of 238 (45.8%) specimens were culture-positive for M. tuberculosis complex (MTBC), and of these, 67 isolates were rifampicin resistant (RIF-R) by phenotypic DST, and 64/67 (95.5%) were isoniazid resistant (INH-R). Compared to culture of the same specimen, a single direct Xpert was more sensitive for detecting MTBC (95.3%, 95% confidence interval [CI], 90.0–98.3%) than direct (59.6%, 95% CI, 50.2–68.5%) or concentrated smear (85.3%, 95% CI, 77.7–91.1%) or LJ culture (80.8%, 95% CI, 72.4–87.5%); specificity was 86.0% (95% CI 78.9–91.3%). Compared with MGIT DST, Xpert correctly identified 98.2% (95% CI, 91.5–99.9%) of RIF-R and 95.5% (95% CI, 85.8–99.2%) of RIF-susceptible (RIF-S) specimens. In a subset of 104 specimens, the sensitivity of TB-Biochip for MTBC detection compared to culture was 97.3% (95% CI, 91.0–99.5%); specificity was 78.1% (95% CI, 61.5– 89.9%). TB-Biochip correctly identified 100% (95% CI, 94.2–100%) of RIF-R, 94.7% (95% CI, 76.7–99.7%) of RIF-S, 98.2% (95% CI, 91.4–99.9%) of INH-R, and 78.6% (95% CI, 52.1–94.2%) of INH-S specimens, compared to MGIT DST. Conclusions Xpert and Biochip were similar in accuracy for detecting MTBC and RIF resistance compared to conventional culture methods. PMID:23263819

  6. Performance of Cepheid ® Xpert MTB/RIF ® and TB-Biochip ® MDR in two regions of Russia with a high prevalence of drug-resistant tuberculosis.

    Science.gov (United States)

    Kurbatova, E V; Kaminski, D A; Erokhin, V V; Volchenkov, G V; Andreevskaya, S N; Chernousova, L N; Demikhova, O V; Ershova, J V; Kaunetis, N V; Kuznetsova, T A; Larionova, E E; Smirnova, T G; Somova, T R; Vasilieva, I A; Vorobieva, A V; Zolkina, S S; Cegielski, J P

    2013-06-01

    The purpose of this study was to assess the performance of Cepheid® Xpert MTB/RIF® ("Xpert") and TB-Biochip® MDR ("TB-Biochip"). Sputum specimens from adults with presumptive tuberculosis (TB) were homogenized and split for: (1) direct Xpert and microscopy, and (2) concentration for Xpert, microscopy, culture [Lowenstein-Jensen (LJ) solid media and Mycobacteria Growth Indicator Tube® (MGIT)], indirect drug susceptibility testing (DST) using the absolute concentration method and MGIT, and TB-Biochip. In total, 109 of 238 (45.8 %) specimens were culture-positive for Mycobacterium tuberculosis complex (MTBC), and, of these, 67 isolates were rifampicin resistant (RIF-R) by phenotypic DST and 64/67 (95.5 %) were isoniazid resistant (INH-R). Compared to culture of the same specimen, a single direct Xpert was more sensitive for detecting MTBC [95.3 %, 95 % confidence interval (CI), 90.0-98.3 %] than direct (59.6 %, 95 % CI, 50.2-68.5 %) or concentrated smear (85.3 %, 95 % CI, 77.7-91.1 %) or LJ culture (80.8 %, 95 % CI, 72.4-87.5 %); the specificity was 86.0 % (95 % CI, 78.9-91.3 %). Compared with MGIT DST, Xpert correctly identified 98.2 % (95 % CI, 91.5-99.9 %) of RIF-R and 95.5 % (95 % CI, 85.8-99.2 %) of RIF-susceptible (RIF-S) specimens. In a subset of 104 specimens, the sensitivity of TB-Biochip for MTBC detection compared to culture was 97.3 % (95 % CI, 91.0-99.5 %); the specificity was 78.1 % (95 % CI, 61.5-89.9 %). TB-Biochip correctly identified 100 % (95 % CI, 94.2-100 %) of RIF-R, 94.7 % (95 % CI, 76.7-99.7 %) of RIF-S, 98.2 % (95 % CI, 91.4-99.9 %) of INH-R, and 78.6 % (95 % CI, 52.1-94.2 %) of INH-S specimens compared to MGIT DST. Xpert and Biochip were similar in accuracy for detecting MTBC and RIF resistance compared to conventional culture methods. PMID:23263819

  7. Blazhko effect in Cepheids and RR Lyrae stars

    CERN Document Server

    Szabó, R

    2013-01-01

    The Blazhko effect is the conspicuous amplitude and phase modulation of the pulsation of RR Lyrae stars that was discovered in the early 20th century. The field of study of this mysterious modulation has recently been invigorated thanks to the space photometric missions providing long, uninterrupted, ultra-precise time series data. In this paper I give a brief overview of the new observational findings related to the Blazhko effect, like extreme modulations, irregular modulation cycles and additional periodicities. I argue that these findings together with dedicated ground-based efforts now provide us with a fairly complete picture and a good starting point to theoretical investigations. Indeed, new, unpredicted dynamical phenomena have been discovered in Blazhko RR Lyrae stars, such as period doubling, high-order resonances, three-mode pulsation and low-dimensional chaos. These led to the proposal of a new explanation to this century-old enigma, namely a high-order resonance between radial modes. Along these...

  8. Robust high-contrast companion detection from interferometric observations. The CANDID algorithm and an application to six binary Cepheids

    OpenAIRE

    Gallenne, A.; Mérand, A.; Kervella, P; Monnier, J. D.; Schaefer, G. H.; Baron, F; Breitfelder, J.; Bouquin, J. B. Le; Roettenbacher, R. M.; Gieren, W.; Pietrzynski, G.; McAlister, H.; Brummelaar, T. ten; Sturmann, J.; Sturmann, L.

    2015-01-01

    Long-baseline interferometry is an important technique to spatially resolve binary or multiple systems in close orbits. By combining several telescopes together and spectrally dispersing the light, it is possible to detect faint components around bright stars. Aims. We provide a rigorous and detailed method to search for high-contrast companions around stars, determine the detection level, and estimate the dynamic range from interferometric observations. We developed the code CANDID (Companio...

  9. Novel cost-effective quality control approach for the Cepheid Xpert CT/NG assay for the detection of Chlamydia Trachomatis and Neisseria Gonorrhoeae.

    Science.gov (United States)

    Chan, Maurice; Jiang, Boran; Ng, Siew Yong Lily; Tan, Thean Yen

    2016-06-01

    The Xpert CT/NG is a rapid assay for detection of Neisseria gonorrhoeae and Chlamydia trachomatis. QC materials must be formulated to emulate human specimens, and are prohibitively expensive. A creative, cost-effective QC approach is proposed. The acceptable sample types for the Xpert CT/NG assay were extended to include eye swabs. PMID:27091503

  10. Prospective and retrospective evaluation of the Cepheid Xpert® Flu/RSV XC assay for rapid detection of influenza A, influenza B, and respiratory syncytial virus.

    Science.gov (United States)

    Salez, Nicolas; Nougairede, Antoine; Ninove, Laetitia; Zandotti, Christine; de Lamballerie, Xavier; Charrel, Remi N

    2015-04-01

    A total of 281 clinical specimens (nasal swabs and nasopharyngeal aspirates) were tested with the Xpert® Flu/RSV XC. The results were compared to those obtained with the real-time retro transcriptase-polymerase chain reaction assays routinely used in our laboratory. The Xpert® Flu/RSV XC showed sensitivity/specificity of 97.8%/100% and 97.9%/100% for flu and respiratory syncytial virus, respectively. PMID:25662018

  11. Cepheid distances from the SpectroPhoto-Interferometry of Pulsating Stars (SPIPS) - Application to the prototypes delta Cep and eta Aql

    CERN Document Server

    Merand, Antoine; Breitfelder, Joanne; Gallenne, Alexandre; Foresto, Vincent Coude du; Brummelaar, Theo A ten; McAlister, Harold A; Ridgway, Stephen; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H

    2015-01-01

    The parallax of pulsation, and its implementations such as the Baade-Wesselink method and the infrared surface bright- ness technique, is an elegant method to determine distances of pulsating stars in a quasi-geometrical way. However, these classical implementations in general only use a subset of the available observational data. Freedman & Madore (2010) suggested a more physical approach in the implementation of the parallax of pulsation in order to treat all available data. We present a global and model-based parallax-of-pulsation method that enables including any type of observational data in a consistent model fit, the SpectroPhoto-Interferometric modeling of Pulsating Stars (SPIPS). We implemented a simple model consisting of a pulsating sphere with a varying effective temperature and a combina- tion of atmospheric model grids to globally fit radial velocities, spectroscopic data, and interferometric angular diameters. We also parametrized (and adjusted) the reddening and the contribution of the cir...

  12. Comparison of Cepheid Xpert Flu/RSV XC and BioFire FilmArray for Detection of Influenza A, Influenza B, and Respiratory Syncytial Virus.

    Science.gov (United States)

    Wahrenbrock, Mark G; Matushek, Scott; Boonlayangoor, Sue; Tesic, Vera; Beavis, Kathleen G; Charnot-Katsikas, Angella

    2016-07-01

    The Xpert Flu/RSV XC was compared to the FilmArray respiratory panel for detection of influenza (Flu) A, Flu B, and respiratory syncytial virus (RSV), using 128 nasopharyngeal swabs. Positive agreements were 100% for Flu A and RSV and 92.3% for Flu B. The Xpert may be useful in clinical situations when extensive testing is not required and may serve an important role in laboratories already performing broader respiratory panel testing. PMID:27098956

  13. Comparison of the Abbott m2000 RealTime CT Assay and the Cepheid GeneXpert CT/NG Assay to the Roche Amplicor CT Assay for Detection of Chlamydia trachomatis in Ocular Samples from Tanzania

    OpenAIRE

    Dize, Laura; West, Sheila; Williams, James A; Van Der Pol, Barbara; Quinn, Thomas C.; Gaydos, Charlotte A.

    2013-01-01

    The GeneXpert CT/NG assay (GeneXpert) and the Abbott m2000 RealTime CT (m2000) assay were compared to Amplicor for detecting ocular Chlamydia trachomatis. Discordant specimens were tested by the Aptima CT assay. The m2000 assay sensitivity was 100% (95% confidence interval [CI], 90% to 100%), and specificity was 98.46% (95% CI, 95.2% to 99.2%); GeneXpert sensitivity was 100% (95% CI, 90% to 100%), and specificity was 100% (95% CI, 98.1% to 100%). The m2000 and GeneXpert assays appear to perfo...

  14. Pinning down the Milky Way's spin

    Science.gov (United States)

    2008-09-01

    New, very precise measurements have shown that the rotation of the Milky Way is simpler than previously thought. A remarkable result from the most successful ESO instrument HARPS, shows that a much debated, apparent 'fall' of neighbourhood Cepheid stars towards our Sun stems from an intrinsic property of the Cepheids themselves. First Light of the PRIMA Instrument ESO PR Photo 30/08 Cepheids in the Solar Neighbourhood The result, obtained by a group of astrophysicists led by Nicolas Nardetto, will soon appear in the journal Astronomy & Astrophysics. Since Henrietta Leavitt's discovery of their unique properties in 1912, the class of bright, pulsating stars known as Cepheids has been used as a distance indicator. Combined with velocity measurements, the properties of Cepheids are also an extremely valuable tool in investigations of how our galaxy, the Milky Way, rotates. "The motion of Milky Way Cepheids is confusing and has led to disagreement among researchers," says Nardetto. "If the rotation of the Galaxy is taken into account, the Cepheids appear to 'fall' towards the Sun with a mean velocity of about 2 km/s." A debate has raged for decades as to whether this phenomenon was truly related to the actual motion of the Cepheids and, consequently, to a complicated rotating pattern of our galaxy, or if it was the result of effects within the atmospheres of the Cepheids. Nardetto and his colleagues observed eight Cepheids with the high precision HARPS spectrograph, attached to the 3.6-m ESO telescope at La Silla, 2400 m up in the mountains of the Chilean Atacama Desert. HARPS, or the High Accuracy Radial Velocity Planetary Searcher, is best known as a very successful planet hunter, but it can also be used to resolve other complicated cases, where its ability to determine radial velocities - the speed with which something is moving towards or away from us - with phenomenally high accuracy is invaluable. "Our observations show that this apparent motion towards us almost

  15. A 2.4% Determination of the Local Value of the Hubble Constant

    CERN Document Server

    Riess, Adam G; Hoffmann, Samantha L; Scolnic, Dan; Casertano, Stefano; Filippenko, Alexei V; Tucker, Brad E; Reid, Mark J; Jones, David O; Silverman, Jeffrey M; Chornock, Ryan; Challis, Peter; Yuan, Wenlong; Foley, Ryan J

    2016-01-01

    We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant (H_0) from 3.3% to 2.4%. Improvements come from observations of Cepheid variables in 10 new hosts of recent SNe~Ia, more than doubling the sample of SNe~Ia having a Cepheid-calibrated distance for a total of 18; these leverage the magnitude-redshift relation based on 300 SNe~Ia at z<0.15. All 18 hosts and the megamaser system NGC4258 were observed with WFC3, thus nullifying cross-instrument zeropoint errors. Other improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC4258, more Cepheids and a more robust distance to the LMC from late-type DEBs, HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (i) megamasers in NGC4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes, and (iv) 2 DEBs in M31. The...

  16. THE M31 NEAR-INFRARED PERIOD-LUMINOSITY RELATION AND ITS NON-LINEARITY FOR δ Cep VARIABLES WITH 0.5 ≤ log (P) ≤ 1.7

    Energy Technology Data Exchange (ETDEWEB)

    Kodric, Mihael; Riffeser, Arno; Seitz, Stella; Hopp, Ulrich; Goessl, Claus [University Observatory Munich, Scheinerstrasse 1, D-81679 Munich (Germany); Snigula, Jan; Lee, Chien-Hsiu; Koppenhoefer, Johannes; Bender, Ralf [Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, D-85748 Garching (Germany); Gieren, Wolfgang, E-mail: kodric@usm.lmu.de [Departamento de Astronomia, Universidad de Concepciòn, Casilla 160-C, Concepciòn (Chile)

    2015-02-01

    We present the largest M31 near-infrared (F110W (close to J band), F160W (H band)) Cepheid sample so far. The sample consists of 371 Cepheids with photometry obtained from the Hubble Space Telescope PHAT program. The sample of 319 fundamental mode Cepheids, 16 first overtone Cepheids, and 36 type II Cepheids was identified using the median absolute deviation outlier rejection method we develop here. This method does not rely on priors and allows us to obtain this clean Cepheid sample without rejecting a large fraction of Cepheids. The obtained period-luminosity relations (PLRs) have a very small dispersion, i.e., 0.155 mag in F160W, despite using random phased observations. This remarkably small dispersion allows us to determine that the PLRs are significantly better described by a broken slope at 10 days than a linear slope. The use of our sample as an anchor to determine the Hubble constant gives a 3.2% larger Hubble constant compared to the Riess et al. sample.

  17. The M31 Near-Infrared Period-Luminosity Relation and its non-linearity for $\\delta$ Cep Variables with $0.5 \\leq \\log(P) \\leq 1.7$

    CERN Document Server

    Kodric, Mihael; Seitz, Stella; Snigula, Jan; Hopp, Ulrich; Lee, Chien-Hsiu; Goessl, Claus; Koppenhoefer, Johannes; Bender, Ralf; Gieren, Wolfgang

    2014-01-01

    We present the largest M31 near-infrared (F110W, F160W) Cepheid sample so far. The sample consists of 374 Cepheids with photometry obtained from the HST PHAT program. The sample of 322 fundamental mode Cepheids, 16 first overtone Cepheids and 36 type II Cepheids, was derived using the median absolute deviation (MAD) outlier rejection method we develop here. This method does not rely on priors and allows us to obtain this clean Cepheid sample without rejecting a large fraction of Cepheids. The obtained Period-Luminosity relations (PLRs) have a very small dispersion, i.e. 0.156 mag in F160W, despite using random phased observations. This remarkably small dispersion allows us to determine that the PLRs are significantly better described by a broken slope at ten days than a linear slope. The Hubble constant based on our improved PLRs is $69.5 \\pm 2.4~\\mathrm{km}~\\mathrm{s}^{-1}~\\mathrm{Mpc}^{-1}$ which is significantly smaller than the Riess et al. (2012) value and consistent with the Planck value (Planck Collabo...

  18. Preliminary Analysis of ULPC Light Curves Using Fourier Decomposition Technique

    CERN Document Server

    Ngeow, Chow-Choong; Kanbur, Shashi; Barrett, Brittany; Lin, Bin

    2013-01-01

    Recent work on Ultra Long Period Cepheids (ULPCs) has suggested their usefulness as a distance indicator, but has not commented on their relationship as compared with other types of variable stars. In this work, we use Fourier analysis to quantify the structure of ULPC light curves and compare them to Classical Cepheids and Mira variables. Our preliminary results suggest that the low order Fourier parameters of ULPCs show a continuous trend defined by Classical Cepheids after the resonance around 10 days. However their Fourier parameters also overlapped with those from Miras, which make the classification of long period variable stars difficult based on the light curves information alone.

  19. Variable stars in the Pegasus dwarf galaxy (DDO 216)

    International Nuclear Information System (INIS)

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

  20. The Magellanic Clouds

    International Nuclear Information System (INIS)

    It is known that mira variables in the Large Magellanic Cloud (LMC) show an infrared period-luminosity relation. The refinement of the period-luminosity relation of cepheids and miras has been advanced at the South African Astronomical Observatory (SAAO) during 1986. Studies undertaken at SAAO have included: the mira period-luminosity relation in the LMC; the young cluster NGC 1866 and its cepheids; cepheids in the Magellanic Clouds; RR Lyraes in Magellanic Cloud clusters; carbon and s-type stars in the Magellanic Clouds, and old LMC clusters. 2 figs

  1. Nonradial Oscillations in Classical Pulsating Stars. Predictions and Discoveries

    CERN Document Server

    Dziembowski, W A

    2015-01-01

    After a brief historical introduction and recalling basic concepts of stellar oscillation theory, I focus my review on interpretation of secondary periodicities found in RR Lyrae stars and Cepheids as a manifestation of nonradial mode excitation.

  2. Carnegie Hubble Program: A Mid-Infrared Calibration of the Hubble Constant

    Science.gov (United States)

    Freedman, Wendy L.; Madore, Barry F.; Scowcroft, Victoria; Burns, Chris; Monson, Andy; Persson, S. Eric; Seibert, Mark; Rigby, Jane

    2012-01-01

    Using a mid-infrared calibration of the Cepheid distance scale based on recent observations at 3.6 micrometers with the Spitzer Space Telescope, we have obtained a new, high-accuracy calibration of the Hubble constant. We have established the mid-IR zero point of the Leavitt law (the Cepheid period-luminosity relation) using time-averaged 3.6 micrometers data for 10 high-metallicity, MilkyWay Cepheids having independently measured trigonometric parallaxes. We have adopted the slope of the PL relation using time-averaged 3.6micrometers data for 80 long-period Large Magellanic Cloud (LMC) Cepheids falling in the period range 0.8 baryon acoustic oscillations yield w(sub 0) = -1.08 +/- 0.10 and a value of N(sub eff) = 4.13 +/- 0.67, mildly consistent with the existence of a fourth neutrino species.

  3. The history and development of nonlinear stellar pulsation codes

    International Nuclear Information System (INIS)

    This review is limited to the history and development of nonlinear stellar pulsation codes and methods. The narrative includes examples of practical interest in the application of these numerical methods to problems in stellar pulsation such as Cepheid mass discrepancy, the delineation of the RR Lyrae instability strip, and the question of the development of double-mode pulsation as observed in Cepheids, RR Lyrae and other variable stars. 15 refs

  4. Highlights on eclipsing binary variables from Araucaria Project

    Directory of Open Access Journals (Sweden)

    Karczmarek Paulina

    2015-01-01

    Full Text Available The Araucaria Project, which main goal is to provide precise determination of the cosmic distance scale, has recently made a set of discoveries involving variable stars in binary systems. Among these discoveries we highlight three: 1% precise measurement of a Cepheid's dynamical mass and its projection factor, accurate determination of both stellar and orbital parameters of eclipsing binary consisting of two Cepheid variables, and discovery of new class of variable stars, mimicking RR Lyrae pulsators.

  5. The Araucaria Project

    OpenAIRE

    Pietrzynski, G.; Gieren, W.

    2005-01-01

    {Results from a long-term observational project called the Araucaria Project are presented. Based on Wide Field optical monitoring of 8 nearby galaxies, covering a large range of metallicities, more than 500 Cepheids and a few hundred Blue Supergiant candidates were identified. From the analysis of Cepheid P-L relations of outstanding quality derived from our data we conclude that the slope of these relations in the I band and Wesenheit index are not dependent on metallicity. Comparing the I-...

  6. The Carnegie Hubble Program

    Science.gov (United States)

    Freedman, Wendy L.; Madore, Barry F.; Scowcroft, Vicky; Mnso, Andy; Persson, S. E.; Rigby, Jane; Sturch, Laura; Stetson, Peter

    2011-01-01

    We present an overview of and preliminary results from an ongoing comprehensive program that has a goal of determining the Hubble constant to a systematic accuracy of 2%. As part of this program, we are currently obtaining 3.6 micron data using the Infrared Array Camera (IRAC) on Spitzer, and the program is designed to include JWST in the future. We demonstrate that the mid-infrared period-luminosity relation for Cepheids at 3.6 microns is the most accurate means of measuring Cepheid distances to date. At 3.6 microns, it is possible to minimize the known remaining systematic uncertainties in the Cepheid extragalactic distance scale. We discuss the advantages of 3.6 micron observations in minimizing systematic effects in the Cepheid calibration of the Hubble constant including the absolute zero point, extinction corrections, and the effects of metallicity on the colors and magnitudes of Cepheids. We are undertaking three independent tests of the sensitivity of the mid-IR Cepheid Leavitt Law to metallicity, which when combined will allow a robust constraint on the effect. Finally, we are providing a new mid-IR Tully-Fisher relation for spiral galaxies.

  7. The pulsating variable star population in DDO210

    Science.gov (United States)

    Ordoñez, Antonio J.; Sarajedini, Ata

    2016-01-01

    We have probed the pulsating variable star content of the isolated Local Group dwarf galaxy, DDO210 (Aquarius), using archival Advanced Camera for Surveys/Hubble Space Telescope imaging in the F475W and F814W passbands. We find a total of 32 RR Lyrae stars (24 ab-type; 8 c-type) and 75 Cepheid variables. The mean periods of the ab-type and c-type RR Lyrae stars are calculated to be = 0.609 ± 0.011 and = 0.359 ± 0.025 d, respectively. The light-curve properties of the fundamental mode RR Lyrae stars yield a mean metallicity of = -1.63 ± 0.11 dex for this ancient population, consistent with a recent synthetic colour-magnitude diagram analysis. We find this galaxy to be Oosterhoff-intermediate and lacking in high-amplitude, short-period ab-type RR Lyrae, consistent with behaviour recently observed for many dwarf spheroidals and ultrafaint dwarfs in the Local Group. We find a distance modulus of μ = 25.07 ± 0.12 as determined by the RR Lyrae stars, slightly larger but agreeing with recent distance estimates from the red giant branch tip. We also find a sizable population of Cepheid variables in this galaxy. We provide evidence in favour of most if not all of these stars being short-period classical Cepheids. Assuming all of these stars to be classical Cepheids, we find that most of these Cepheids are ˜300 Myr old, with the youngest Cepheids being offset from the older Cepheids and the centre of the galaxy. We conclude that this may have resulted from a migration of star formation in DDO210.

  8. The Carnegie Hubble Program: The Leavitt Law at 3.6 microns and 4.5 microns in the Large Magellanic Cloud

    Science.gov (United States)

    Scowcroft, Victoria; Freedman, Wendy L.; Madore, Barry F.; Monson, Andrew J.; Persson, S. E.; Seibert, Mark; Rigby, Jane R.; Sturch, Laura

    2011-01-01

    The Carnegie Hubble Program (CHP) is designed to improve the extragalactic distance scale using data from the post-cryogenic era of Spitzer. The ultimate goal is a determination of the Hubble constant to an accuracy of 2%. This paper is the first in a series on the Cepheid population of the Large Magellanic Cloud, and focuses on the period-luminosity relations (Leavitt laws) that will be used, in conjunction with observations of Milky Way Cepheids, to set the slope and zero-point of the Cepheid distance scale in the mid-infrared. To this end, we have obtained uniformly-sampled light curves for 85 LMC Cepheids, having periods between 6 and 140 days. Period- luminosity and period-color relations are presented in the 3.6 micron and 4.5 micron bands. We demonstrate that the 3.6 micron band is a superb distance indicator. The cyclical variation of the [3.6]-[4.5] color has been measured for the first time. We attribute the amplitude and phase of the color curves to the dissociation and recombination of CO molecules in the Cepheid s atmosphere. The CO affects only the 4.5 micron flux making it a potential metallicity indicator.

  9. A 3% Solution: Determination of the Hubble Constant with the Hubble Space Telescope and Wide Field Camera 3

    CERN Document Server

    Riess, Adam G; Casertano, Stefano; Lampeitl, Hubert; Ferguson, Henry C; Filippenko, Alexei V; Jha, Saurabh W; Li, Weidong; Chornock, Ryan

    2011-01-01

    We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to determine the Hubble constant (H0) from optical and infrared observations of over 600 Cepheid variables in the host galaxies of 8 recent Type Ia supernovae (SNe Ia), providing the calibration for a mag-z relation of 253 SNe Ia. Increased precision over past measurements comes from: (1) more than doubling the number of infrared observations of Cepheids in nearby SN hosts; (2) increasing the sample of ideal SN Ia calibrators from six to eight; (3) increasing by 20% the number of Cepheids with infrared observations in the megamaser host NGC 4258; (4) reducing the difference in the mean metallicity of the Cepheid comparison samples from \\Delta log [O/H] = 0.08 to 0.05; and (5) calibrating all optical Cepheid colors with one camera, WFC3, to remove cross-instrument zero-point errors. Uncertainty in H0 from beyond the 1st rung of the distance ladder is reduced from 3.5% to 2.3%. The measurement of H0 via the geometric distance to NGC 4258 is 74....

  10. Absorption-line profiles in a companion spectrum of a mass-losing cool supergiant

    Science.gov (United States)

    Rodrigues, Liliya L.; Boehm-Vitense, Erika

    1992-01-01

    Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculated absorption line profiles that would be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star wind and for different orbital phases of the binary. Bowen and Wilson find theoretically that stellar pulsations drive mass loss. We therefore apply our calculations to the Cepheid binary S Muscae which has a B5V companion. We find an upper limit for the Cepheid mass loss of M less than or equal to 7 x 10 (exp -10) solar mass per year provided that the stellar wind of the companion does not influence the Cepheid wind at large distances.

  11. Absorption line profiles in a companion spectrum of a mass losing cool supergiant

    Science.gov (United States)

    Rodrigues, Liliya L.; Boehm-Vitense, Erika

    1990-01-01

    Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculated absorption line profiles that would be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star wind and for different orbital phases of the binary. Bowen and Wilson find theoretically that stellar pulsations drive mass loss. We therefore apply our calculations to the Cepheid binary S Muscae which has a B5V companion. We find an upper limit for the Cepheid mass loss of M less than or equal to 7 x 10(exp -10) solar mass per year provided that the stellar wind of the companion does not influence the Cepheid wind at large distances.

  12. Double-mode pulsation

    International Nuclear Information System (INIS)

    Double mode pulsation is a very pervasive phenomenon in stars all over the Hertzsprung-Russell diagram. In order of increasing radius, examples are: ZZ Ceti stars, the sun, the delta Scuti stars, RR Lyrae variables, the β Cephei variables and those related to them, Cepheids, and maybe even the Mira stars. These many modes have been interpreted as both radial and nonradial modes, but in many cases the actual mode has not been clearly identified. Yellow giants seem to be the most simple pulsators with a large majority of the RR Lyrae variables and Cepheids showing only one pulsation period. We limit this review to those very few cases for classical Cepheids and RR Lyrae variables which display two modes. For these we know many facts about these stars, but the actual cause of the pulsation in two modes simultaneously remains unknown

  13. Astrophysical Tests of Modified Gravity: Constraints from Distance Indicators in the Nearby Universe

    CERN Document Server

    Jain, Bhuvnesh; Sakstein, Jeremy

    2012-01-01

    We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators -- cepheids, tip of the red giant branch (TRGB) stars, and water masers -- operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered in opposite directions over a range of chameleon gravity theory parameters, well below the sensitivity of cosmological probes. Using published data we have compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. As a control sample we use a comparable set of screened galaxies. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background ...

  14. Estimation of the Vertical Disk Scale Height Using Young Galactic Objects

    CERN Document Server

    Bobylev, V V

    2016-01-01

    We have collected literature data on young Galactic objects such as masers with VLBI-measured trigonometric parallaxes, OB associations, HII regions and Cepheids. We have recently established that vertical disk scale height is strongly influenced by the objects of the Local arm. In the present work we used samples that do not contain objects in this arm. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h=46+/-5 pc from 69 masers with trigonometric parallaxes, h=36+/-3 pc from 59 OB associations, h=35.6+/-2.7 pc from 147 HII regions, h=52.1+/-1.9 pc from 195 young Cepheids, and h=72.0+/-2.3 pc from 192 old Cepheids.

  15. A new analysis of the Red Giant Branch "Tip" distance scale and the value of the Hubble constant

    CERN Document Server

    Salaris, M

    1998-01-01

    The theoretical evaluations of the Red Giant Branch Tip (TRGB) luminosity presented in Salaris & Cassisi (1997) are extended to higher metallicities, and compared with analogous independent results recently published. The comparison between our ZAHB and TRGB distance scales for galactic globular clusters presented in Salaris & Cassisi (1997) is now supplemented with a comparison with the HIPPARCOS distance scale set by local subdwarfs with accurate parallax determinations. The overall agreement between ZAHB and HIPPARCOS distances is quite good. The ZAHB and TRGB distances to resolved galaxies are in good agreement, whereas the comparison between TRGB and Cepheid distances, computed by using the calibration suggested by Madore & Freedman (1991), reveals a systematic discrepancy of the order of 0.12 mag. The TRGB distances are systematically longer in comparison with the Cepheid ones. This result supports the case for a revision of the zero point of the Cepheid distance scale, as already suggested ...

  16. On the pulsation and evolutionary properties of helium burning radially pulsating variables

    Science.gov (United States)

    Bono, G.; Pietrinferni, A.; Marconi, M.; Braga, V. F.; Fiorentino, G.; Stetson, P. B.; Buonanno, R.; Castellani, M.; Dall'Ora, M.; Fabrizio, M.; Ferraro, I.; Giuffrida, G.; Iannicola, G.; Marengo, M.; Magurno, D.; Martinez-Vazquez, C. E.; Matsunaga, N.; Monelli, M.; Neeley, J.; Rastello, S.; Salaris, M.; Short, L.; Stellingwerf, R. F.

    2016-05-01

    We discuss pulsation and evolutionary properties of low- (RR Lyrae, Type II Cepheids) and intermediate-mass (Anomalous Cepheids) radial variables. We focus our attention on the topology of the instability strip and the distribution of the quoted variables in the Hertzsprung-Russell diagram. We discuss their evolutionary status and the dependence on the metallicity. Moreover, we address the diagnostics (period derivative, difference in luminosity, stellar mass) that can provide solid constraints on their progenitors and on the role that binarity and environment have in shaping their current pulsation characteristics. Finally, we briefly outline their use as standard candles.

  17. La dynamique atmosphérique des Céphéides et l'étalonnage des échelles de distance dans l'Univers

    OpenAIRE

    Nardetto, Nicolas

    2005-01-01

    Applying the Interferometric Baade-Wesselink method, hereafter IBW method, toVINCI/VLTI observations we determine the distance of seven Cepheids. For l Car, the more resolved star, we obtain an uncertainty on the derived distance of 5%. We also calibrate the zero-point of the Cepheid P-L relation with an uncertainty of 0.08 in magnitude. Interferometric measurements lead to angular diameter estimations over the whole pulsation period, while the stellar radius variations can be deduced from th...

  18. The Optical Gravitational Lensing Experiment. Variable stars in the Sculptor dwarf speroidal galaxy

    OpenAIRE

    Kaluzny, J.; Kubiak, M.; Szymanski, M.; Udalski, A; Krzeminski, W.; M Mateo

    1994-01-01

    The central area of the Sculptor dwarf galaxy was surveyed for variable stars as a side-program of the OGLE project. Light curves in the V band were obtained for 226 RR Lyr stars and for 3 anomalous cepheids. One previously unknown anomalous cepheid was identified. We discovered also two variables located at the tip of the red giant branch of Sculptor. Out of 226 RR Lyr variables 135 were classified as RRab, 88 as RRc and 2 as RRd. Distribution of periods for RRab stars shows a sharp cut-off ...

  19. Non-LTE Abundances of Magnesium, Aluminum and Sulfur in OB Stars Near the Solar Circle

    OpenAIRE

    Daflon, S.; Cunha, K.; Smith, V.V.; Butler, K.

    2002-01-01

    Non-LTE abundances of magnesium, aluminum and sulfur are derived for a sample of 23 low-v \\sin i stars belonging to six northern OB associations of the Galactic disk within 1 kpc of the Sun. The abundances are obtained from the fitting of synthetic line profiles to high resolution spectra. A comparison of our results with HII region abundances indicates good agreement for sulfur while the cepheid abundances are higher. The derived abundances of Mg show good overlap with the cepheid results. T...

  20. The Magellanic clouds

    International Nuclear Information System (INIS)

    As the two galaxies nearest to our own, the Magellanic Clouds hold a special place in studies of the extragalactic distance scale, of stellar evolution and the structure of galaxies. In recent years, results from the South African Astronomical Observatory (SAAO) and elsewhere have shown that it is possible to begin understanding the three dimensional structure of the Clouds. Studies of Magellanic Cloud Cepheids have continued, both to investigate the three-dimensional structure of the Clouds and to learn more about Cepheids and their use as extragalactic distance indicators. Other research undertaken at SAAO includes studies on Nova LMC 1988 no 2 and red variables in the Magellanic Clouds

  1. A 3% SOLUTION: DETERMINATION OF THE HUBBLE CONSTANT WITH THE HUBBLE SPACE TELESCOPE AND WIDE FIELD CAMERA 3

    International Nuclear Information System (INIS)

    We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to determine the Hubble constant from optical and infrared observations of over 600 Cepheid variables in the host galaxies of eight recent Type Ia supernovae (SNe Ia), providing the calibration for a magnitude-redshift relation based on 253 SNe Ia. Increased precision over past measurements of the Hubble constant comes from five improvements: (1) more than doubling the number of infrared observations of Cepheids in the nearby SN hosts; (2) increasing the sample size of ideal SN Ia calibrators from six to eight; (3) increasing by 20% the number of Cepheids with infrared observations in the megamaser host NGC 4258; (4) reducing the difference in the mean metallicity of the Cepheid comparison samples between NGC 4258 and the SN hosts from Δlog [O/H] = 0.08 to 0.05; and (5) calibrating all optical Cepheid colors with a single camera, WFC3, to remove cross-instrument zero-point errors. The result is a reduction in the uncertainty in H0 due to steps beyond the first rung of the distance ladder from 3.5% to 2.3%. The measurement of H0 via the geometric distance to NGC 4258 is 74.8 ± 3.1 km s-1 Mpc-1, a 4.1% measurement including systematic uncertainties. Better precision independent of the distance to NGC 4258 comes from the use of two alternative Cepheid absolute calibrations: (1) 13 Milky Way Cepheids with trigonometric parallaxes measured with HST/fine guidance sensor and Hipparcos and (2) 92 Cepheids in the Large Magellanic Cloud for which multiple accurate and precise eclipsing binary distances are available, yielding 74.4 ± 2.5 km s-1 Mpc-1, a 3.4% uncertainty including systematics. Our best estimate uses all three calibrations but a larger uncertainty afforded from any two: H0 = 73.8 ± 2.4 km s-1 Mpc-1 including systematic errors, corresponding to a 3.3% uncertainty. The improved measurement of H0, when combined with the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year data, results in

  2. Carnegie Hubble Program: A Mid-Infrared Calibration of the Hubble Constant

    CERN Document Server

    Freedman, Wendy L; Scowcroft, Victoria; Burns, Chris; Monson, Andy; Persson, S Eric; Seibert, Mark; Rigby, Jane

    2012-01-01

    Using a mid-infrared calibration of the Cepheid distance scale based on recent observations at 3.6 um with the Spitzer Space Telescope, we have obtained a new, high-accuracy calibration of the Hubble constant. We have established the mid-IR zero point of the Leavitt Law (the Cepheid Period-Luminosity relation) using time-averaged 3.6 um data for ten high-metallicity, Milky Way Cepheids having independently-measured trigonometric parallaxes. We have adopted the slope of the PL relation using time-averaged 3.6 um data for 80 long-period Large Magellanic Cloud (LMC) Cepheids falling in the period range 0.8 < log(P) < 1.8. We find a new reddening-corrected distance to the LMC of 18.477 +/- 0.033 (systematic) mag. We re-examine the systematic uncertainties in H0, also taking into account new data over the past decade. In combination with the new Spitzer calibration, the systematic uncertainty in H0 over that obtained by the Hubble Space Telescope (HST) Key Project has decreased by over a factor of three. App...

  3. GAIA and the Extragalactic Distance Scale

    CERN Document Server

    Tammann, G A

    2002-01-01

    The local expansion field (v<1200kms-1) and the cosmic expansion field out to 30000kms-1 are characterized by Ho=58. While the random error of this determination is small (+-2 units), it may still be affected by systematic errors as large as +-10%. The local expansion is outlined by Cepheids and by Cepheid-calibrated TF distances of a complete sample by field galaxies and by nearby groups and clusters; the cosmic expansion is defined by Cepheid-calibrated SNeIa. The main source of systematic errors are therefore the shape and the zero point of the P-L relation of Cepheids and its possible dependence on metallicity. GAIA will essentially eliminate these systematic error sources. Another source of systematic error is due to the homogenization of SNeIa as to decline rate Delta m_{15} and color (B-V). GAIA will discover ~ 850 SNeIa within 10000kms-1 during its four-year lifetime. If their photometric parameters can be determined from the ground, they will fix the dependence of the SNeIa luminosity on Delta m_{...

  4. REVISITING THE ABUNDANCE GRADIENT IN THE MASER HOST GALAXY NGC 4258

    International Nuclear Information System (INIS)

    New spectroscopic observations of 36 H II regions in NGC 4258 obtained with the Gemini telescope are combined with existing data from the literature to measure the radial oxygen abundance gradient in this galaxy. The [O III]λ4363 auroral line was detected in four of the outermost targets (17-22 kpc from the galaxy center), allowing a determination of the electron temperature Te of the ionized gas. From the use of different calibrations of the R23 abundance indicator, an oxygen abundance gradient of approximately -0.012 ± 0.002 dex kpc-1 is derived. Such a shallow gradient, combined with the difference in the distance moduli measured from the Cepheid period-luminosity relation by Macri et al. between two distinct fields in NGC 4258, would yield an unrealistically strong effect of metallicity on the Cepheid distances. This strengthens the suggestion that systematic biases might affect the Cepheid distance of the outer field. Evidence for a similar effect in the differential study of M33 by Scowcroft et al. is presented. A revision of the transformation between strong-line and Te -based abundances in Cepheid-host galaxies is discussed. In the Te abundance scale, the oxygen abundance of the inner field of NGC 4258 is found to be comparable with the LMC value.

  5. Classical variables in the era of space photometric missions

    Directory of Open Access Journals (Sweden)

    Molnár L.

    2015-01-01

    Full Text Available The space photometric missions like CoRoT and Kepler transformed our view of pulsating stars, including the well-known RR Lyrae and Cepheid classes. The K2, TESS and PLATO missions will expand these investigations to larger sample sizes and to specific stellar populations.

  6. Evaluation of Xpert® Norovirus Assay performance in comparison with real-time RT-PCR in hospitalized adult patients with acute gastroenteritis.

    Science.gov (United States)

    Rovida, Francesca; Premoli, Marta; Campanini, Giulia; Sarasini, Antonella; Baldanti, Fausto

    2016-08-01

    Xpert® Norovirus Assay (Cepheid, Sunnyvale, CA) was compared with a laboratory-developed real-time RT-PCR assay for the detection of Norovirus GI and GII in hospitalized patients with acute gastroenteritis. The two assays showed a high level of concordance but Xpert® Norovirus Assay allowed faster detection of Norovirus and a simpler sample handling. PMID:27233425

  7. The Carnegie Hubble Program: The Leavitt Law at 3.6 \\mu m and 4.5 \\mu m in the Large Magellanic Cloud

    CERN Document Server

    Scowcroft, Victoria; Madore, Barry F; Monson, Andrew J; Persson, S E; Seibert, Mark; Rigby, Jane R; Sturch, Laura

    2011-01-01

    The Carnegie Hubble Program (CHP) is designed to improve the extragalactic distance scale using data from the post-cryogenic era of Spitzer. The ultimate goal is a determination of the Hubble constant to an accuracy of 2%. This paper is the first in a series on the Cepheid population of the Large Magellanic Cloud, and focusses on the period-luminosity relations (Leavitt laws) that will be used, in conjunction with observations of Milky Way Cepheids, to set the slope and zero--point of the Cepheid distance scale in the mid-infrared. To this end, we have obtained uniformly-sampled light curves for 85 LMC Cepheids, having periods between 6 and 140 days. Period-luminosity and period-color relations are presented in the 3.6 \\mu m and 4.5\\mu m bands. We demonstrate that the 3.6 \\mu m band is a superb distance indicator. The cyclical variation of the [3.6]-[4.5] color has been measured for the first time. We attribute the amplitude and phase of the color curves to the dissociation and recombination of CO molecules i...

  8. Galactic neutrino communication and SETI

    International Nuclear Information System (INIS)

    In this talk I summarize some work done over the last few years about how advanced civilizations across the galaxy may be using neutrinos to communicate in a variety of ways and sending signals as well as using high energy neutrino beams to modulate the periods of Cepheid variable stars.

  9. The HST Key Project on the Extragalactic Distance Scale XXVI The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant

    CERN Document Server

    Ferrarese, L; Kennicutt, R C; Huchra, J P; Ford, H C; Freedman, W L; Stetson, P B; Madore, B F; Sakai, S; Gibson, B K; Graham, J A; Hughes, S M; Illingworth, G D; Kelson, D D; Macri, L M; Silbermann, N A; Sebo, K; Ferrarese, Laura; Mould, Jeremy R.; Kennicutt, Robert C.; Huchra, John; Ford, Holland C.; Freedman, Wendy L.; Stetson, Peter B.; Madore, Barry F.; Sakai, Shoko; Gibson, Brad K.; Graham, John A.; Hughes, Shaun M.; Illingworth, Garth D.; Kelson, Daniel D.; Macri, Lucas; Silbermann, N A; Sebo, Kim

    1999-01-01

    A Cepheid-based calibration is derived for four distance indicators that utilize stars in the old stellar populations: the tip of the red giant branch (TRGB), the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF) and the surface brightness fluctuation method (SBF). The calibration is largely based on the Cepheid distances to 18 spiral galaxies within cz =1500 km/s obtained as part of the HST Key Project on the Extragalactic Distance Scale, but relies also on Cepheid distances from separate HST and ground-based efforts. The newly derived calibration of the SBF method is applied to obtain distances to four Abell clusters in the velocity range between 3800 and 5000 km/s, observed by Lauer et al. (1998) using the HST/WFPC2. Combined with cluster velocities corrected for a cosmological flow model, these distances imply a value of the Hubble constant of H0 = 69 +/- 4 (random) +/- 6 (systematic) km/s/Mpc. This result assumes that the Cepheid PL relation is independent of th...

  10. Galactic neutrino communication and SETI

    Energy Technology Data Exchange (ETDEWEB)

    Pakvasa, Sandip [Department of Physics and Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

    2010-11-01

    In this talk I summarize some work done over the last few years about how advanced civilizations across the galaxy may be using neutrinos to communicate in a variety of ways and sending signals as well as using high energy neutrino beams to modulate the periods of Cepheid variable stars.

  11. A combined value of the Hubble constant

    International Nuclear Information System (INIS)

    We combine measurements of the Hubble constant in M100, M96, NGC 5253 and IC 4182 including the correction due to the metallicity dependence of the period-luminosity relation of Cepheids, as determined by Beaulieu et al. and Sasselov et al. We pay special attention to error correlations

  12. Parallax beyond a kiloparsec from spatially scanning the wide field Camera 3 on the Hubble space telescope

    Energy Technology Data Exchange (ETDEWEB)

    Riess, Adam G.; Casertano, Stefano [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Anderson, Jay; MacKenty, John [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Filippenko, Alexei V., E-mail: ariess@stsci.edu [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States)

    2014-04-20

    We use a newly developed observing mode on the Hubble Space Telescope (HST) and Wide Field Camera 3, spatial scanning, to increase source sampling a thousand-fold and measure changes in source positions to a precision of 20-40 μas, more than an order of magnitude better than attainable in pointed observations. This observing mode can usefully measure the parallaxes of bright stars at distances of up to 5 kpc, a factor of 10 farther than achieved thus far with HST. The technique should also provide a unique crosscheck of future parallax measurements from Gaia. Long-period classical Cepheid variable stars in the Milky Way, nearly all of which reside beyond 1 kpc, are especially compelling targets for parallax measurements from scanning, as they may be used to anchor a determination of the Hubble constant to ∼1%. We illustrate the method by measuring to high precision the parallax of a classical Cepheid, SY Aurigae, at a distance of more than 2 kpc, using five epochs of spatial-scan data obtained at intervals of six months. Rapid spatial scans also enable photometric measurements of bright Milky Way Cepheids—which would otherwise saturate even in the shortest possible pointed observations—on the same flux scale as extragalactic Cepheids, which is a necessity for reducing a leading source of systematic error in the Hubble constant. We demonstrate this capability with photometric measurements of SY Aur on the same system used for Cepheids in Type Ia supernova host galaxies. While the technique and results presented here are preliminary, an ongoing program with HST is collecting such parallax measurements for another 18 Cepheids to produce a better anchor for the distance scale.

  13. CHP-II: The Carnegie Hubble Program to Measure Ho to 3% Using Population II

    Science.gov (United States)

    Rich, Jeffrey; Freedman, Wendy L.; Madore, Barry F.; Monson, Andy; Scowcroft, Victoria; Beaton, Rachael; Kollmeier, Juna A.; Seibert, Mark; Bono, Giuseppe; Clementini, Gisella; Yang, Soung-Chul; Lee, Myung Gyoon; Jang, In Sung

    2015-01-01

    There has been great progress in the measurement of cosmological parameters in recent years, but controversy has arisen over the Planck/WMAP versus the direct measurement of the Hubble constant. The goal of our Carnegie Hubble Program (CHP) is to obtain a direct measure of Ho to 3%. In CHP I, we used Cepheid variables to calibrate the extragalactic distance scale. In the second phase, CHP II, we are establishing a completely independent route to Ho using RR Lyrae variables, the tip of the red giant branch (TRGB) and Type Ia supernovae (SNe Ia). Not only is the RR Lyrae route independent of the Cepheids, but its PL relation has a scatter that is a factor of 2 smaller. Unlike the Cepheids, the RR Lyrae / TRGB distance scale can be applied to both elliptical and spiral galaxies. This is a great systematic advantage, given the small number of galaxies (9 in total) close enough to have measured Cepheid calibrators within the SNIa hosts. By providing a new calibration using a Pop II distance scale, we will immediately double the number of SN Ia distances based on geometry, linking to over 200 SNe in the pure Hubble flow out to z = 0.7. Four calibrators containing both Cepheids and TRGB stars provide an important cross-check on systematics. Initially, the accuracy of our value of Ho will be set by four galactic RR Lyrae calibrators with HST/FGS parallaxes. With Gaia, both the RR Lyrae zero point and TRGB method will be independently calibrated with at least an order of magnitude more calibrators, each having precisions of 1% or better. This will allow the highest accuracy measurement of Ho to date using the "Distance Ladder" method.

  14. Parallax beyond a kiloparsec from spatially scanning the wide field Camera 3 on the Hubble space telescope

    International Nuclear Information System (INIS)

    We use a newly developed observing mode on the Hubble Space Telescope (HST) and Wide Field Camera 3, spatial scanning, to increase source sampling a thousand-fold and measure changes in source positions to a precision of 20-40 μas, more than an order of magnitude better than attainable in pointed observations. This observing mode can usefully measure the parallaxes of bright stars at distances of up to 5 kpc, a factor of 10 farther than achieved thus far with HST. The technique should also provide a unique crosscheck of future parallax measurements from Gaia. Long-period classical Cepheid variable stars in the Milky Way, nearly all of which reside beyond 1 kpc, are especially compelling targets for parallax measurements from scanning, as they may be used to anchor a determination of the Hubble constant to ∼1%. We illustrate the method by measuring to high precision the parallax of a classical Cepheid, SY Aurigae, at a distance of more than 2 kpc, using five epochs of spatial-scan data obtained at intervals of six months. Rapid spatial scans also enable photometric measurements of bright Milky Way Cepheids—which would otherwise saturate even in the shortest possible pointed observations—on the same flux scale as extragalactic Cepheids, which is a necessity for reducing a leading source of systematic error in the Hubble constant. We demonstrate this capability with photometric measurements of SY Aur on the same system used for Cepheids in Type Ia supernova host galaxies. While the technique and results presented here are preliminary, an ongoing program with HST is collecting such parallax measurements for another 18 Cepheids to produce a better anchor for the distance scale.

  15. A 2.4% Determination of the Local Value of the Hubble Constant

    Science.gov (United States)

    Riess, Adam G.; Macri, Lucas M.; Hoffmann, Samantha L.; Scolnic, Dan; Casertano, Stefano; Filippenko, Alexei V.; Tucker, Brad E.; Reid, Mark J.; Jones, David O.; Silverman, Jeffrey M.; Chornock, Ryan; Challis, Peter; Yuan, Wenlong; Brown, Peter J.; Foley, Ryan J.

    2016-07-01

    We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new near-infrared (NIR) observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on ∼300 SNe Ia at z instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC 4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (i) megamasers in NGC 4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes measured with HST/FGS, HST/WFC3 spatial scanning and/or Hipparcos, and (iv) 2 DEBs in M31. The Hubble constant from each is 72.25 ± 2.51, 72.04 ± 2.67, 76.18 ± 2.37, and 74.50 ± 3.27 km s‑1 Mpc‑1, respectively. Our best estimate of H 0 = 73.24 ± 1.74 km s‑1 Mpc‑1 combines the anchors NGC 4258, MW, and LMC, yielding a 2.4% determination (all quoted uncertainties include fully propagated statistical and systematic components). This value is 3.4σ higher than 66.93 ± 0.62 km s‑1 Mpc‑1 predicted by ΛCDM with 3 neutrino flavors having a mass of 0.06 eV and the new Planck data, but the discrepancy reduces to 2.1σ relative to the prediction of 69.3 ± 0.7 km s‑1 Mpc‑1 based on the comparably precise combination of WMAP+ACT+SPT+BAO observations, suggesting that systematic uncertainties in CMB radiation measurements may play a role in the tension. If we

  16. A REDETERMINATION OF THE HUBBLE CONSTANT WITH THE HUBBLE SPACE TELESCOPE FROM A DIFFERENTIAL DISTANCE LADDER

    International Nuclear Information System (INIS)

    This is the second of two papers reporting results from a program to determine the Hubble constant to ∼5% precision from a refurbished distance ladder based on extensive use of differential measurements. Here we report observations of 240 Cepheid variables obtained with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) Camera 2 through the F160W filter on the Hubble Space Telescope (HST). The Cepheids are distributed across six recent hosts of Type Ia supernovae (SNe Ia) and the 'maser galaxy' NGC 4258, allowing us to directly calibrate the peak luminosities of the SNe Ia from the precise, geometric distance measurements provided by the masers. New features of our measurement include the use of the same instrument for all Cepheid measurements across the distance ladder and homogeneity of the Cepheid periods and metallicities, thus necessitating only a differential measurement of Cepheid fluxes and reducing the largest systematic uncertainties in the determination of the fiducial SN Ia luminosity. In addition, the NICMOS measurements reduce the effects of differential extinction in the host galaxies by a factor of ∼5 over past optical data. Combined with a greatly expanded set of 240 SNe Ia at z 0 = 74.2 ± 3.6 km s-1 Mpc-1, a 4.8% uncertainty including both statistical and systematic errors. To independently test the maser calibration, we use 10 individual parallax measurements of Galactic Cepheids obtained with the HST fine guidance sensor and find similar results. We show that the factor of 2.2 improvement in the precision of H 0 is a significant aid to the determination of the equation-of-state parameter of dark energy, w = P/(ρc2). Combined with the Wilkinson Microwave Anisotropy Probe five-year measurement of ΩM h2, we find w = -1.12 ± 0.12 independent of any information from high-redshift SNe Ia or baryon acoustic oscillations (BAO). This result is also consistent with analyses based on the combination of high-redshift SNe Ia and BAO. The

  17. The evolution of stars of medium mass

    International Nuclear Information System (INIS)

    The main properties of the evolution of intermediate- and high-mass stars are reviewed, focusing on a few issues tightly related to the interpretation of population I Cepheid stars. The classical results of stellar evolution theory are given for the main evolutionary phases (main sequence, core He-burning, and later) all over the H-R diagram, putting into evidence the various points of disagreement with current observational data. The models incorporating the effect of convective overshoot are discussed, and a study on the rich young cluster NGC 1866 in the Large Magellanic Cloud is presented in which the models are compared with the observational data. Arguments are given to favor the adoption of models with convective overshoot instead of the classical ones. The topics of the mass discrepancy and number frequency-period distribution of Cepheid stars are then discussed in light of models with convective overshoot, arguing that these latter can better account for the observational data. 95 refs

  18. Quantitative results of stellar evolution and pulsation theories.

    Science.gov (United States)

    Fricke, K.; Stobie, R. S.; Strittmatter, P. A.

    1971-01-01

    The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

  19. The Recognition of Unusual Objects in the Sloan Digital Sky Survey Color System

    CERN Document Server

    Krisciunas, K; Szkody, P; Krisciunas, Kevin; Margon, Bruce; Szkody, Paula

    1998-01-01

    We present 5 filter photometry of 21 carbon stars, 15 asteroids, 15 cataclysmic variables, 6 metal-poor stars, 5 Cepheids, 1775 field stars, blue horizontal branch (BHB) stars and RR Lyrae stars in the globular clusters M 15 and M 2, two primary standards, and 19 secondary standards. The photometry was carried out using a filter set identical to that which will be used for the Sloan Digital Sky Survey. We find that carbon stars, CVs, R-type, J-type, and V-type asteroids, BHB stars, and RR Lyr stars should be identifiable on the basis of SDSS photometry alone, while Cepheids, metal-poor stars, and many types of asteroids are indistinguishable from the stellar locus of field stars.

  20. UPSILoN: AUtomated Classification of Periodic Variable Stars using MachIne LearNing

    Science.gov (United States)

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

    2015-12-01

    UPSILoN (AUtomated Classification of Periodic Variable Stars using MachIne LearNing) classifies periodic variable stars such as Delta Scuti stars, RR Lyraes, Cepheids, Type II Cepheids, eclipsing binaries, and long-period variables (i.e. superclasses), and their subclasses (e.g. RR Lyrae ab, c, d, and e types) using well-sampled light curves from any astronomical time-series surveys in optical bands regardless of their survey-specific characteristics such as color, magnitude, and sampling rate. UPSILoN consists of two parts, one which extracts variability features from a light curve, and another which classifies a light curve, and returns extracted features, a predicted class, and a class probability. In principle, UPSILoN can classify any light curves having arbitrary number of data points, but using light curves with more than ~80 data points provides the best classification quality.

  1. Analysis of the Z Distribution of Young Objects in the Galactic Thin Disk

    CERN Document Server

    Bobylev, V V

    2015-01-01

    We have obtained new estimates of the Sun's distance from the symmetry plane Zo and the vertical disk scale height h using currently available data on stellar OB associations, Wolf-Rayet stars, HII regions, and Cepheids. Based on individual determinations, we have calculated the mean Zo=-16+/-2 pc. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h = 40.2+/-2.1 pc from OB associations, h = 47.8+/-3.9 pc from Wolf-Rayet stars, h=48.4+/-2.5 pc from HII regions, and h = 66.2+/-1.6 pc from Cepheids. We have estimated the surface, \\sum=6 kpc^{-2}, and volume, D(Zo) = 50.6 kpc^{-3}, densities from a sample of OB associations. We have found that there could be approximately 5000 OB associations in the Galaxy.

  2. RR Lyrae Stars In The GCVS Observed By The Qatar Exoplanet Survey

    CERN Document Server

    Bramich, D M; Ferro, A Arellano; Parley, N R; Cameron, A Collier; Horne, K; Pollacco, D; West, R G

    2014-01-01

    We used the light curve archive of the Qatar Exoplanet Survey (QES) to investigate the RR Lyrae variable stars listed in the General Catalogue of Variable Stars (GCVS). Of 588 variables studied, we reclassify 14 as eclipsing binaries, one as an RS Canum Venaticorum-type variable, one as an irregular variable, four as classical Cepheids, and one as a type II Cepheid, while also improving their periods. We also report new RR Lyrae sub-type classifications for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae variables. There are seven double-mode RR Lyrae stars in the sample for which we measured their fundamental and first overtone periods. Finally, we detect the Blazhko effect in 38 of the RR Lyrae stars for the first time and we successfully measured the Blazhko period for 26 of them.

  3. Oxygen, $\\alpha$-element and iron abundance distributions in the inner part of the Galactic thin disc. II

    CERN Document Server

    Andrievsky, S M; Kovtyukh, V V; Korotin, S A; Lépine, J R D

    2016-01-01

    We have derived the abundances of 36 chemical elements in one Cepheid star, ASAS 181024--2049.6, located R$_{\\rm G}= 2.53$ kpc from the Galactic center. This star falls within a region of the inner thin disc poorly sampled in Cepheids. Our spectral analysis shows that iron, magnesium, silicon, calcium and titanium LTE abundances in that star support the presence of a plateau-like abundance distribution in the thin disc within 5 kpc of the Galactic center, as previously suggested by \\cite{Maret15}. If confirmed, the flattening of the abundance gradient within that region could be the result of a decrease in the star formation rate due to dynamic effects, possibly from the central Galactic bar.

  4. 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.

  5. Comparison of Three Commercial Molecular Assays for Detection of Rifampin and Isoniazid Resistance among Mycobacterium tuberculosis Isolates in a High-HIV-Prevalence Setting.

    Science.gov (United States)

    Strydom, K; Ismail, F; Matabane, M M Z; Onwuegbuna, O; Omar, S V; Ismail, N

    2015-09-01

    In a head-to-head comparison of the MTBDRplus version 2.0 (Hain Lifescience), the Xpert MTB/RIF (Cepheid), and the Anyplex MTB/NTM (Seegene) assays, we demonstrated equal sensitivity (59/61; 96.7%) and specificity (53/54; 98.1%) for detecting rifampin resistance with further analysis of discordances. The Xpert assay does not detect isoniazid resistance while the Anyplex assay showed high false positivity. PMID:26135869

  6. Stellar candles for the extragalactic distance scale

    CERN Document Server

    Gieren, Wolfgang

    2003-01-01

    This volume reviews the current status with respect to both theory and observation of the extragalactic distance scale. A sufficient accuracy is required both for a precise determination of the cosmological parameters and also in order to achieve a better understanding of physical processes in extragalactic systems. The "standard candles", used to set up the extragalactic distance scale, reviewed in this book include cepheid variables, RR Lyrae variables, novae, Type Ia and Type II supernovae as well as globular clusters and planetary nebulae.

  7. The boundary line in the H-R diagram for stellar chromospheres and the theory of convection

    Science.gov (United States)

    Boehm-Vitense, E.; Dettmann, T.

    1980-01-01

    Ultraviolet emission-line spectra of A, F, and early G stars have been observed with the International Ultraviolet Explorer. For supergiants, classical chromospheric and transition-layer emission is seen only on the red side of the Cepheid instability strip. For luminosity classes III-V, chromospheric emission can be detected for spectral types F2 and later. For none of the A stars was normal chromospheric emission detected, regardless of their rotational velocities or peculiarities (i.e., Am or Ap).

  8. Nonlinear simulations of the convection-pulsation coupling

    OpenAIRE

    Gastine, T.; Dintrans, B.

    2011-01-01

    In cold Cepheids close to the red edge of the classical instability strip, a strong coupling between the stellar pulsations and the surface convective motions occurs. This coupling is by now poorly described by 1-D models of convection, the so-called "time-dependent convection models" (TDC). The intrinsic weakness of such models comes from the large number of unconstrained free parameters entering in the description of turbulent convection. A way to overcome these limits is to compute two-dim...

  9. Les Céphéides et l'échelle des distances galactiques: apport de l'interférométrie à longue base

    OpenAIRE

    Breitfelder, Joanne

    2015-01-01

    Cepheids have been used since more than a century as standard candles to estimate distances in the Universe, owing to the relation between their pulsation period and absolute magnitude. The calibration of this relation (also called "Leavitt law", in homage to its discoverer) is based on independent distance estimates, that are generally derived from the parallax-of-pulsation method. This rather simple technique makes a comparison of the angular diameter variation (measured for example through...

  10. The effect of rapid screening for methicillin-resistant Staphylococcus aureus (MRSA) on the identification and earlier isolation of MRSA-positive patients.

    LENUS (Irish Health Repository)

    Creamer, Eilish

    2010-04-01

    (1) To determine whether rapid screening with polymerase chain reaction (PCR) assays leads to the earlier isolation of patients at risk for methicillin-resistant Staphylococcus aureus (MRSA) colonization, (2) to assess compliance with routine MRSA screening protocols, (3) to confirm the diagnostic accuracy of the Xpert MRSA real-time PCR assay (Cepheid) by comparison with culture, and (4) to compare turnaround times for PCR assay results with those for culture results.

  11. Comparison of Xpert Flu rapid nucleic acid testing with rapid antigen testing for the diagnosis of influenza A and B

    OpenAIRE

    DiMaio, Michael A.; Sahoo, Malaya K.; Waggoner, Jesse; Pinsky, Benjamin A.

    2012-01-01

    Influenza infections are associated with thousands of hospital admissions and deaths each year. Rapid detection of influenza is important for prompt initiation of antiviral therapy and appropriate patient triage. In this study the Cepheid Xpert Flu assay was compared with two rapid antigen tests, BinaxNOW Influenza A & B and BD Directigen EZ Flu A + B, as well as direct fluorescent antibody testing for the rapid detection of influenza A and B. Using real-time, hydrolysis probe-based, reverse ...

  12. H$_{0}$ and odds on cosmology

    CERN Document Server

    Jaffe, A

    1995-01-01

    Recent observations by the Hubble Space Telescope of Cepheids in the Virgo cluster imply a Hubble Constant H_0=80\\pm17\\ km/sec/Mpc. We attempt to clarify some issues of interpretation of these results for determining the global cosmological parameters \\Omega and \\Lambda. Using the formalism of Bayesian model comparison, the data suggest a universe with a nonzero cosmological constant \\Lambda>0, but vanishing curvature: \\Omega+\\Lambda=1.

  13. The Large Magellanic Cloud and the Distance Scale

    OpenAIRE

    Walker, Alistair R.

    2011-01-01

    The Magellanic Clouds, especially the Large Magellanic Cloud, are places where multiple distance indicators can be compared with each other in a straight-forward manner at considerable precision. We here review the distances derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing Binaries, and show that the results from these distance indicators generally agree to within their errors, and the distance modulus to the Large Magellanic Cloud appears to be defined to 3% wit...

  14. The Distances of the Magellanic Clouds

    OpenAIRE

    Walker, Alistair R.

    1998-01-01

    The present status of our knowledge of the distances to the Magellanic Clouds is evaluated from a post-Hipparcos perspective. After a brief summary of the effects of structure, reddening, age and metallicity, the primary distance indicators for the Large Magellanic Cloud are reviewed: The SN 1987A ring, Cepheids, RR Lyraes, Mira variables, and Eclipsing Binaries. Distances derived via these methods are weighted and combined to produce final "best" estimates for the Magellanic Clouds distance ...

  15. Evaluation of the Xpert Flu Rapid PCR Assay in High-Risk Emergency Department Patients

    Science.gov (United States)

    Valsamakis, Alexandra; Gaydos, Charlotte A.; Forman, Michael; Hardick, Justin; Kidambi, Pranav; Amin, Sharmeen; Gupta, Alisha; Rothman, Richard E.

    2014-01-01

    We prospectively evaluated the performance of Cepheid's GeneXpert Xpert Flu assay in a target population of 281 adults presenting to the emergency department with an acute respiratory illness who met Centers for Disease Control and Prevention (CDC) criteria for recommended antiviral treatment. Compared with the Prodesse ProFlu+ assay, Xpert Flu had an overall sensitivity of 95.3% and specificity of 99.2%. PMID:25253792

  16. Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations

    OpenAIRE

    Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; Liu, Michael C.; Rieke, Marcia J.; Ajhar, Edward A.; Blakeslee, John P

    2002-01-01

    To empirically calibrate the IR surface brightness fluctuation (SBF) distance scale and probe the properties of unresolved stellar populations, we measured fluctuations in 65 galaxies using NICMOS on the Hubble Space Telescope. The early-type galaxies in this sample include elliptical and S0 galaxies and spiral bulges in a variety of environments. Absolute fluctuation magnitudes in the F160W (1.6 micron) filter were derived for each galaxy using previously-measured I-band SBF and Cepheid vari...

  17. Clinical utility of the Xpert MRSA assay for early detection of methicillin-resistant Staphylococcus aureus

    OpenAIRE

    OH, AE-CHIN; Lee, Jin Kyung; LEE, HA NA; HONG, YOUNG JUN; Chang, Yoon Hwan; Hong, Seok-Il; Kim, Dong Ho

    2012-01-01

    Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for many nosocomial and community-acquired infections, resulting in significant morbidity and mortality. A practical way to limit the spread of MRSA is early detection and proper treatment. However, screening culture for MRSA typically requires 2–3 days. The Xpert MRSA assay (Cepheid, Sunnyvale, CA, USA) is a real-time polymerase chain reaction-based assay developed for screening an MRSA-specific DNA sequence within the staphyl...

  18. Constraining Dust Extinction Properties via the VVV Survey

    CERN Document Server

    Majaess, D; Dekany, I; Minniti, D; Gieren, W

    2016-01-01

    Near-infrared color-excess and extinction ratios are essential for establishing the cosmic distance scale and probing the Galaxy, particularly when analyzing targets attenuated by significant dust. A robust determination of those ratios followed from leveraging new infrared observations from the VVV survey, wherein numerous bulge RR Lyrae and Type II Cepheids were discovered, in addition to $BVJHK_{s}(3.4\\rightarrow22)\\mu m$ data for classical Cepheids and O-stars occupying the broader Galaxy. The apparent optical color-excess ratios vary significantly with Galactic longitude ($\\ell$), whereas the near-infrared results are comparatively constant with $\\ell$ and Galactocentric distance ($\\langle E(J-\\overline{3.5\\mu m})/E(J-K_s) \\rangle =1.28\\pm0.03$). The results derived imply that classical Cepheids and O-stars display separate optical trends ($R_{V,BV}$) with $\\ell$, which appear to disfavor theories advocating a strict and marked decrease in dust size with increasing Galactocentric distance. The classical ...

  19. The Carnegie Hubble Program: The Leavitt Law at 3.6 and 4.5 micron in the Milky Way

    CERN Document Server

    Monson, Andrew J; Madore, Barry F; Persson, S E; Scowcroft, Victoria; Seibert, Mark; Rigby, Jane R

    2012-01-01

    The Carnegie Hubble Program (CHP) is designed to calibrate the extragalactic distance scale using data from the post-cryogenic era of the Spitzer Space Telescope. The ultimate goal of the CHP is a systematic improvement in the distance scale leading to a determination of the Hubble Constant to within an accuracy of 2%. This paper focuses on the measurement and calibration of the Galactic Cepheid Period-Luminosity (Leavitt) Relation using the warm Spitzer IRAC 1 and 2 bands at 3.6 and 4.5 \\mu m. We present photometric measurements covering the period range 4 - 70 days for 37 Galactic Cepheids. Data at 24 phase points were collected for each star. Three PL relations of the form M=a(Log(P)-1)+b are derived. The method adopted here takes the slope a to be -3.31, as determined from the Spitzer LMC data of Scowcroft et al. (2012). Using the geometric HST guide-star distances to ten Galactic Cepheids we find a calibrated 3.6 micron PL zero-point of -5.80\\pm0.03. Together with our value for the LMC zero-point we dete...

  20. Large Magellanic Cloud Near-Infrared Synoptic Survey. II. The Wesenheit relations and their application to the Distance scale

    CERN Document Server

    Bhardwaj, Anupam; Macri, Lucas M; Singh, Harinder P; Ngeow, Chow-Choong; Wagner-Kaiser, R; Sarajedini, Ata

    2015-01-01

    We present new near-infrared Cepheid Period-Wesenheit relations in the LMC using time-series observations from the Large Magellanic Cloud Near-Infrared Synoptic Survey. We also derive optical$+$near-infrared P-W relations using $V$ and $I$~magnitudes from OGLE-III. We employ our new $JHK_s$ data to determine an independent distance to the LMC of $\\mu_{\\rm LMC} = 18.47\\pm0.07 {\\textit{(statistical)}}$~mag, using an absolute calibration of the Galactic relations based on several distance determination methods and accounting for the intrinsic scatter of each technique. We also derive new near-infrared Period-Luminosity and Wesenheit relations for Cepheids in M31 using observations from the PHAT survey. We use the absolute calibrations of the Galactic and LMC $W_{J,H}$ relations to determine the distance modulus of M31, $\\mu_{\\rm M31} = 24.46\\pm0.20$~mag. We apply a simultaneous fit to Cepheids in several Local Group galaxies covering a range of metallicities ($7.7<12+\\log[O/H]<8.6$~dex) to determine a glob...

  1. Large Magellanic Cloud Near-Infrared Synoptic Survey. III. A Statistical Study of Non-Linearity in the Leavitt Laws

    CERN Document Server

    Bhardwaj, Anupam; Macri, Lucas M; Singh, Harinder P; Ngeow, Chow-Choong; Ishida, Emille E O

    2016-01-01

    We present a detailed statistical analysis of possible non-linearities in the Period-Luminosity (P-L), Period-Wesenheit (P-W) and Period-Color (P-C) relations for Cepheid variables in the LMC at optical ($VI$) and near-infrared ($JHK_{s}$) wavelengths. We test for the presence of possible non-linearities and determine their statistical significance by applying a variety of robust statistical tests ($F$-test, Random-Walk, Testimator and the Davies test) to optical data from OGLE III and near-infrared data from LMCNISS. For fundamental-mode Cepheids, we find that the optical P-L, P-W and P-C relations are non-linear at 10 days. The near-infrared P-L and the $W^H_{V,I}$ relations are non-linear around 18 days; this break is attributed to a distinct variation in mean Fourier amplitude parameters near this period for longer wavelengths as compared to optical bands. The near-infrared P-W relations are also non-linear except for the $W_{H,K_s}$ relation. For first-overtone mode Cepheids, a significant change in the ...

  2. Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields

    Science.gov (United States)

    Pietrukowicz, P.; Dziembowski, W. A.; Mróz, P.; Soszyński, I.; Udalski, A.; Poleski, R.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, Ł.; Ulaczyk, K.; Kozłowski, S.; Skowron, J.

    2013-12-01

    We present the results of a search for pulsating stars in the 7.12 deg2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 31 Long-Period Variables, such as Miras and Semi-Regular Variables, one pulsating white dwarf, and 58 very likely δ Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode δ Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5 MSun and are located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. Our sample also includes candidates for Type II Cepheids and unclassified short-period (Phistory of the Milky Way, we have already compiled a list of known Galactic Classical Cepheids.

  3. Pulsating Star Mystery Solved

    Science.gov (United States)

    2010-11-01

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

  4. ESA's Hipparcos satellite revises the scale of the cosmos

    Science.gov (United States)

    1997-02-01

    This ruler relies on the brightnesses of winking stars called Cepheids, but the distances of the nearest examples, which calibrate the ruler, could only be estimated. Direct measurements by Hipparcos imply that the Cepheids are more luminous and more distant than previously imagined. The brightnesses of Cepheids seen in other galaxies are used as a guide to their distances. All of these galaxies may now be judged to lie farther away. At the same time the Hipparcos Cepheid scale drastically reduces the ages of the oldest stars, to about 11 billion years. By a tentative interpretation the Universe is perhaps 12 billion years old. Michael Feast from the University of Cape Town, South Africa, announces his conclusion about the Cepheids at a meeting devoted to Hipparcos at the Royal Astronomical Society in London today (14 February 1997). It will provoke much comment and controversy, because the scale and age of the Universe is the touchiest issue in cosmology. The best hope for confirming or modifying the result now rests with studies using Hipparcos data on other kinds of variable stars. An investigation of the variables called Miras, by Floor van Leeuwen of Royal Greenwich Observatory, Cambridge, and his colleagues, is described at the same London meeting. Full scientific reports on both the Cepheids and Miras have been accepted for publication in a leading journal, the Monthly Notices of the Royal Astronomical Society. European teams of scientists and engineers conceived and launched the unique Hipparcos satellite, which operated from 1989 to 1993. Hipparcos fixed precise positions in the sky of 120,000 stars (Hipparcos Catalogue) and logged a million more with a little less accuracy (Tycho Catalogue). Since 1993 the largest computations in the history of astronomy have reconciled the observations, to achieve a hundredfold improvement in the accuracy of star positions compared with previous surveys. Slight seasonal shifts in stellar positions as the Earth orbits the

  5. Discovery in the Galactic Bulge

    Science.gov (United States)

    Kohler, Susanna

    2015-11-01

    In our efforts to map our galaxys structure, one region has remained very difficult to probe: the galactic center. A new survey, however, uses infrared light to peer through the gas and dust in the galactic plane, searching for variable stars in the bulge of the galaxy. This study has discovered a population of very young stars in a thin disk in the galactic center, providing clues to the star formation history of the Milky Way over the last 100 million years.Obscured CenterThe center of the Milky Way is dominated by a region known as the galactic bulge. Efforts to better understand this region in particular, its star formation history have been hindered by the stars, gas, and dust of the galactic disk, which prevent us from viewing the galactic bulge at low latitudes in visible light.The positions of the 35 classical Cepheids discovered in VVV data, projected onto an image of the galactic plane. Click for a better look! The survey area is bounded by the blue lines, and the galactic bar is marked with a red curve. The bottom panel shows the position of the Cepheids overlaid on the VVV bulge extinction map. [Dkny et al. 2015]Infrared light, however, can be used to probe deeper through the dust than visible-light searches. A new survey called VISTA Variables in the Via Lactea (VVV) uses the VISTA telescope in Chile to search, in infrared, for variable stars in the inner part of the galaxy. The VVV survey area spans the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high.Led by Istvn Dkny, a researcher at the Millennium Institute of Astrophysics and the Pontifical Catholic University of Chile, a team has now used VVV data to specifically identify classical Cepheid variable stars in the bulge. Why? Cepheids are pulsating stars with a very useful relation between their periods and luminosities that allows them to be used as distance indicators. Moreover, classical Cepheids are indicators of young stellar populations which can

  6. DISTANCE SCALE ZERO POINTS FROM GALACTIC RR LYRAE STAR PARALLAXES

    Energy Technology Data Exchange (ETDEWEB)

    Benedict, G. Fritz; McArthur, Barbara E.; Barnes, Thomas G. [McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Feast, Michael W. [Centre for Astrophysics, Cosmology and Gravitation, Astronomy Department, University of Cape Town, Rondebosch 7701 (South Africa); Harrison, Thomas E. [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Bean, Jacob L.; Kolenberg, Katrien [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Menzies, John W.; Laney, C. D. [South African Astronomical Observatory, Observatory 7935 (South Africa); Chaboyer, Brian [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Fossati, Luca [Department of Physics and Astronomy, Open University, Milton Keynes MK7 6AA (United Kingdom); Nesvacil, Nicole [Institute of Astronomy, University of Vienna, A-1180 Vienna (Austria); Smith, Horace A. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Kochukhov, Oleg [Department of Physics and Astronomy, Uppsala University, 75120 Uppsala (Sweden); Nelan, Edmund P.; Taylor, Denise [STScI, Baltimore, MD 21218 (United States); Shulyak, D. V. [Institute of Astrophysics, Georg-August-University, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Freedman, Wendy L. [The Observatories, Carnegie Institution of Washington, Pasadena, CA 91101 (United States)

    2011-12-15

    We present new absolute trigonometric parallaxes and proper motions for seven Population II variable stars-five RR Lyr variables: RZ Cep, XZ Cyg, SU Dra, RR Lyr, and UV Oct; and two type 2 Cepheids: VY Pyx and {kappa} Pav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interferometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZ Cep, 2.12 {+-} 0.16 mas; XZ Cyg, 1.67 {+-} 0.17 mas; SU Dra, 1.42 {+-} 0.16 mas; RR Lyr, 3.77 {+-} 0.13 mas; UV Oct, 1.71 {+-} 0.10 mas; VY Pyx, 6.44 {+-} 0.23 mas; and {kappa} Pav, 5.57 {+-} 0.28 mas; an average {sigma}{sub {pi}}/{pi} = 5.4%. With these parallaxes, we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RR Lyrae variable star absolute magnitudes, we then derive zero points for M{sub V} -[Fe/H] and M{sub K} -[Fe/H]-log P relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the distance of the Large Magellanic Cloud. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.

  7. DISTANCE SCALE ZERO POINTS FROM GALACTIC RR LYRAE STAR PARALLAXES

    International Nuclear Information System (INIS)

    We present new absolute trigonometric parallaxes and proper motions for seven Population II variable stars—five RR Lyr variables: RZ Cep, XZ Cyg, SU Dra, RR Lyr, and UV Oct; and two type 2 Cepheids: VY Pyx and κ Pav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interferometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZ Cep, 2.12 ± 0.16 mas; XZ Cyg, 1.67 ± 0.17 mas; SU Dra, 1.42 ± 0.16 mas; RR Lyr, 3.77 ± 0.13 mas; UV Oct, 1.71 ± 0.10 mas; VY Pyx, 6.44 ± 0.23 mas; and κ Pav, 5.57 ± 0.28 mas; an average σπ/π = 5.4%. With these parallaxes, we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RR Lyrae variable star absolute magnitudes, we then derive zero points for MV -[Fe/H] and MK -[Fe/H]-log P relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the distance of the Large Magellanic Cloud. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.

  8. On the metallicity of open clusters. III. Homogenised sample

    Science.gov (United States)

    Netopil, M.; Paunzen, E.; Heiter, U.; Soubiran, C.

    2016-01-01

    Context. Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. Aims: In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. Methods: We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. Results: In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. We found a possible increase of metallicity with age, which, if confirmed, would provide observational evidence for radial migration. Although a statistical significance is given, more studies are certainly needed to exclude selection effects, for example. The comparison of open clusters and Cepheids with recent Galactic models agrees well in general. However, the models do not reproduce the flat gradient of the open clusters in the outer disc. Thus, the effect of radial migration is either underestimated in the models, or an additional mechanism is at work. Conclusions: Apart from the Cepheids, open clusters are the best tracers for metallicity over large Galactocentric distances in the Milky Way. For a sound statistical analysis, a sufficiently large and homogeneous sample of cluster metallicities is needed. Our compilation is currently by far the largest and provides the basis for several basic studies such as the statistical

  9. Validation of Real-Time PCR for Laboratory Diagnosis of Acanthamoeba Keratitis▿

    OpenAIRE

    Thompson, Paul P.; Kowalski, Regis P.; Shanks, Robert M. Q.; Gordon, Y. Jerold

    2008-01-01

    Confirmation of Acanthamoeba keratitis by laboratory diagnosis is the first step in the treatment of this vision-threatening disease. Two real-time PCR TaqMan protocols (the Rivière and Qvarnstrom assays) were developed for the detection of genus-specific Acanthamoeba DNA but lacked clinical validation. We have adapted these assays for the Cepheid SmartCycler II system (i) by determining their real-time PCR limits of detection and amplification efficiencies, (ii) by determining their ability ...

  10. Comparison of three real-time PCR assays for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae in young pregnant women.

    Science.gov (United States)

    Peuchant, Olivia; de Diego, Sabrina; Le Roy, Chloé; Frantz-Blancpain, Sandrine; Hocké, Claude; Bébéar, Cécile; de Barbeyrac, Bertille

    2015-12-01

    We compared 3 commercial real-time PCR assays, the Abbott RealTime CT/NG, the cobas® 4800 CT/NG, and the Cepheid Xpert® CT/NG, for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae in vaginal swabs collected prospectively from pregnant women aged <25 years. The overall agreement among 2 assays ranged from 98.9% to 99.5% with a kappa score between 0.94 and 0.97 for C. trachomatis. For N. gonorrhoeae, the overall agreement was 100%. All kits allowed prompt and specific results for C. trachomatis and N. gonorrhoeae in young pregnant women. PMID:26423658

  11. Abundances in southern Local Group dwarf irregular galaxies

    International Nuclear Information System (INIS)

    We have obtained optical spectrophotometry of H II regions in the southern Local Group dwarf irregular galaxies NGC 6822, WLM and SagDIG. Oxygen abundances are deduced via direct electron temperatures for NGC 6822 and WLM and via an empirical method for all three galaxies. These galaxies conform to the luminosity-abundance relationship for irregular galaxies. Although WLM shows a relatively low abundance, we find it unlikely that this is the cause of the lack of long-period Cepheid variables. (author)

  12. Target selection of classical pulsating variables for space-based photometry

    CERN Document Server

    Plachy, E; Szabó, R; Kolenberg, K; Bányai, E

    2016-01-01

    In a few years the Kepler and TESS missions will provide ultra-precise photometry for thousands of RR Lyrae and hundreds of Cepheid stars. In the extended Kepler mission all targets are proposed in the Guest Observer (GO) Program, while the TESS space telescope will work with full frame images and a ~15-16th mag brightness limit with the possibility of short cadence measurements for a limited number of pre-selected objects. This paper highlights some details of the enormous and important work of the target selection process made by the members of Working Group 7 (WG#7) of the Kepler and TESS Asteroseismic Science Consortium.

  13. AGAPE a microlensing search for dark matter by monitoring pixels

    CERN Document Server

    Gondolo, P; Aurière, M; Baillon, Paul; Bouquet, A; Coupinot, G; Coutures, C; Ghesquière, C; Giraud-Héraud, Yannick; Hecquet, J; Kaplan, J; Le Du, Y; Melchior, A L; Moniez, M; Picat, J P; Soucail, G; Coutures, Ch.

    1996-01-01

    AGAPE is an observational search of massive compact halo objects (MACHOs) in the direction of M31 by means of a novel method: the gravitational microlensing of unresolved stars. The search consists in examining CCD pixel light curves for microlensing features. The high level of temporal stability necessary to detect microlensing events has been achieved, with quiet pixels stable within a factor of two of the photon noise (the brightest ones down to a level of 0.001 mag). The data analysis is still in progress, but hundreds of variable objects (cepheids, novae, ...) have already been found. Among them there are several lightcurves that resemble microlensing events.

  14. Variable stars towards the bulge of M31: the AGAPE catalogue

    OpenAIRE

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

    2004-01-01

    We present the AGAPE astrometric and photometric catalogue of 1579 variable stars in a 14'x10' field centred on M31. This work is the first survey devoted to variable stars in the bulge of M31. The R magnitudes of the objects and the B-R colours suggest that our sample is dominated by red long-period variable stars (LPV), with a possible overlap with Cepheid-like type II stars. Twelve nova candidates are identified. Correlations with other catalogues suggest that 2 novae could be recurrent no...

  15. Variability morphologies in the color-magnitude diagram. Searching for secular variability

    OpenAIRE

    Spano, Maxime; Mowlavi, Nami; Eyer, Laurent; Burki, Gilbert

    2009-01-01

    This work is part of an effort to detect secular variable objects in large scale surveys by analysing their path in color-magnitude diagrams. To this aim, we first present the variability morphologies in the V/V-I diagram of several types of variable stars. They comprise both periodic and non periodic variable stars from the Large Magellanic Cloud, such as classical Cepheids, long period variables or Be and R Coronae Borealis stars, as well as two of the detected secular variable stars in the...

  16. Target selection of classical pulsating variables for space-based photometry

    Science.gov (United States)

    Plachy, E.; Molnar, L.; Szabo, R.; Kolenberg, K.; Banyai, E.

    2016-05-01

    In a few years the Kepler and TESS missions will provide ultra- precise photometry for thousands of RR Lyrae and hundreds of Cepheid stars. In the extended Kepler mission all targets are proposed in the Guest Observer (GO) Program, while the TESS space telescope will work with full frame images and a ~15-16th mag brightness limit with the possibility of short cadence measurements for a limited number of pre-selected objects. This paper highlights some details of the enormous and important work of the target selection process made by the members of Working Group 7 (WG#7) of the Kepler and TESS Asteroseismic Science Consortium.

  17. Thomas Hinsley Astbury: from an English market town schoolroom to the internal constitution of the stars

    CERN Document Server

    Shears, Jeremy

    2012-01-01

    T. H. Astbury (1858-1922) was for many years the much-respected headmaster of a boys' junior school in the English market town of Wallingford. By night he was a dedicated amateur astronomer who enjoyed observing meteors, variable stars and many other objects. He began to search few new variable stars, his first discovery being the bright Cepheid variable, RT Aurigae. This, along with his discovery of 4 other variable stars, brought him to attention of some of the most famous professional astronomers of the age, including Herbert Hall Turner, Frank Dyson and Arthur Eddington.

  18. Variable blue straggler stars in NGC 5466

    International Nuclear Information System (INIS)

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

  19. The Araucaria Project: Dependence of mean K, J, and I absolute magnitudes of red clump stars on metallicity and age

    OpenAIRE

    Pietrzy{ń}ski, G.; Gieren, W.; Udalski, A.

    2003-01-01

    (Abridged) We present results of deep near-infrared JK imaging of LMC, SMC, and the Carina and Fornax dwarf galaxies. A comparison of the extinction-corrected K-band red clump star magnitudes with the tip of the red giant branch magnitude, the mean RR Lyrae star V-band magnitude, and the mean K-band magnitude of Cepheid variables at a period of 10 days (for the LMC and SMC) strongly suggest that the red clump star absolute K-band magnitude has a very low (if any) dependence on metallicity ove...

  20. The Milky Way, The Local Galaxies \\& the IR Tully-Fisher Relation

    OpenAIRE

    Malhotra, Sangeeta; Spergel, David N.; Rhoads, James E; Jing LI

    1996-01-01

    Using the near infrared fluxes of local galaxies derived from COBE/DIRBE J(1.25 $\\mu$m) K (2.2 $\\mu$m) \\& L (3.5 $\\mu$m) band maps and published Cepheid distances, we construct Tully-Fisher (TF) diagrams for the nearby galaxies. The measured dispersions in these luminosity-linewidth diagrams are remarkably small: $\\sigma_J = 0.09$ magnitudes, $\\sigma_K = 0.13$ magnitudes, and $\\sigma_L = 0.20$ magnitudes. For the J and K bands, Monte Carlo simulations give a 95\\% confidence interval upper lim...

  1. Detection of Periodicity Based on Independence Tests - II. Improved Serial Independence Measure

    CERN Document Server

    Zucker, Shay

    2016-01-01

    We introduce an improvement to a periodicity metric we have introduced in a previous paper.We improve on the Hoeffding-test periodicity metric, using the Blum-Kiefer-Rosenblatt (BKR) test. Besides a consistent improvement over the Hoeffding-test approach, the BKR approach turns out to perform superbly when applied to very short time series of sawtoothlike shapes. The expected astronomical implications are much more detections of RR-Lyrae stars and Cepheids in sparse photometric databases, and of eccentric Keplerian radial-velocity (RV) curves, such as those of exoplanets in RV surveys.

  2. Pulsating Components in Binary and Multiple Stellar Systems --- A Catalog of Oscillating Binaries

    OpenAIRE

    Zhou, A. -Y.

    2010-01-01

    We present an up-to-date catalog of pulsating binaries, i.e. the binary and multiple stellar systems containing pulsating components, along with a statistics on them. Compared to the earlier compilation by Soydugan et al.(2006a) of 25 delta Scuti-type `oscillating Algol-type eclipsing binaries' (oEA), the recent collection of 74 oEA by Liakos et al.(2012), and the collection of Cepheids in binaries by Szabados (2003a), the numbers and types of pulsating variables in binaries are now extended....

  3. 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.

  4. Oxygen, {\\alpha}-element and iron abundance distributions in the inner part of the Galactic thin disc

    CERN Document Server

    Martin, R P; Kovtyukh, V V; Korotin, S A; Yegorova, I A; Saviane, Ivo

    2015-01-01

    We derived elemental abundances in 27 Cepheids, the great majority situated within a zone of Galactocentric distances ranging from 5 to 7 kpc. One star of our sample, SU Sct, has a Galactocentric distance of about 3 kpc, and thus falls in a poorly investigated region of the inner thin disc. Our new results, combined with data on abundances in the very central part of our Galaxy taken from literature, show that iron, magnesium, silicon, sulfur, calcium and titanium LTE abundance radial distributions, as well as NLTE distribution of oxygen reveal a plateau-like structure or even positive abundance gradient in the region extending from the Galactic center to about 5 kpc.

  5. Hybrid Neural Networks for Frequency Estimation of Unevenly Sampled Data

    CERN Document Server

    Tagliaferri, R; Milano, L; Barone, F

    1999-01-01

    In this paper we present a hybrid system composed by a neural network based estimator system and genetic algorithms. It uses an unsupervised Hebbian nonlinear neural algorithm to extract the principal components which, in turn, are used by the MUSIC frequency estimator algorithm to extract the frequencies. We generalize this method to avoid an interpolation preprocessing step and to improve the performance by using a new stop criterion to avoid overfitting. Furthermore, genetic algorithms are used to optimize the neural net weight initialization. The experimental results are obtained comparing our methodology with the others known in literature on a Cepheid star light curve.

  6. Gaia, Variable Stars and the Distance Scale

    Science.gov (United States)

    Whitelock, P. A.; Feast, M. W.

    2014-07-01

    Some recent observations of Classical Cepheids, RR Lyrae and Mira variables are used to illustrate their continued importance as standard candles. Gaia will provide a calibration of these stars as distance indicators which should lead to a greatly improved understanding of the formation and evolution of our Galaxy as well as a vital calibration of the extra-galactic distance scale. The importance of infrared observations, as well as a deeper understanding of interstellar reddening and photometric systems, will play a part if the Gaia calibration is to be put to good use.

  7. C. difficile ribotype 027 or 176?

    Science.gov (United States)

    Krutova, Marcela; Matejkova, Jana; Nyc, Otakar

    2014-11-01

    Clostridium difficile is a major nosocomial pathogen of present times. The analysis of 624 C. difficile strains from 11 hospitals in the Czech Republic in 2013 revealed that 40% of isolates belonged to ribotype 176. These results suggest that the incidence of CDI (C. difficile infection) in the Czech Republic has increased probably in connection with C. difficile ribotype 176. The molecular systems Xpert C. difficile Epi assay (Cepheid Inc., Sunnyvale, CA) diagnoses toxigenic strains and supports C. difficile ribotype 027 determination based on three specific target places in the toxigenic C. difficile genome. Twenty-nine strains cultivated from stool specimens were evaluated by the Xpert systems as presumed C. difficile PCR ribotype 027 were confirmed as a C. difficile ribotype 176 based on ribotyping. A further 120 C. difficile strains of ribotype 176 were examined for the presence of genes tcdB, cdtB and deletion in position 117 in the tcdC gene. Our experience shows that due to the correspondence of the target places, C. difficile ribotype 176 may be interpreted as ribotype 027 by Xpert C. difficile Epi assay (Cepheid Inc., Sunnyvale, CA). Further molecular analysis as ribotyping based on capillary electrophoresis is needed to differentiate between C. difficile ribotypes 027 and 176 for appropriate epidemiological situation control on local and national levels. PMID:24970104

  8. NEW EVIDENCE SUPPORTING CLUSTER MEMBERSHIP FOR THE KEYSTONE CALIBRATOR DELTA CEPHEI

    International Nuclear Information System (INIS)

    New and existing UBVJHKs , spectroscopic, NOMAD, Hubble Space Telescope, and revised Hipparcos observations are employed to determine properties for δ Cep and its host star cluster. The multi-faceted approach ensured that uncertainties were mitigated (σ/d ∼ 2%). The following fundamental parameters were inferred for δ Cep: E(B – V) = 0.073 ± 0.018(σ), log τ = 7.9 ± 0.1, and d=272 ± 3(σx-bar) ± 5 (σ) pc. The cluster exhibits a turnoff near B6 (M*/M☉ ∼ 5), and the brightest host cluster members are the supergiants ζ Cep (K1.5Ib) and δ Cep. To within the uncertainties, the two stars share common astrometric parameters (π, μα, μδ, RV ∼ –17 km s–1) and are tied to bluer members via the evolutionary track implied by the cluster's UBVJHKs color-color and color-magnitude diagrams. The cluster's existence is bolstered by the absence of an early-type sequence in color-magnitude diagrams for comparison fields. NOMAD data provided a means to identify potential cluster members (n ∼ 30) and double the existing sample. That number could increase with forthcoming precise proper motions (DASCH) for fainter main-sequence stars associated with classical Cepheids (e.g., δ Cep), which may invariably foster efforts to strengthen the Galactic Cepheid calibration and reduce uncertainties tied to H0.

  9. The VMC survey

    CERN Document Server

    Cioni, Maria-Rosa L

    2015-01-01

    The VISTA survey of the Magellanic Clouds system (VMC) is a public survey project of the European Southern Observatory. It is collecting multi-band near-infrared data across large areas of the Large and Small Magellanic Clouds, the Magellanic Bridge and a few fields in the Magellanic Stream. The combination of great sensitivity to stars below the old main sequence turn off, and the multiplicity at Ks band (at least 12 epochs) make VMC highly suitable for the determination of the spatially resolved star formation history and three-dimensional geometry, using variable stars such as Cepheids and RR Lyrae stars. The VMC observations are progressing well and will be completed in 2018. The VMC survey has a high legacy value and many science results have already been published, e.g. the most detailed star formation history map of the Small Magellanic Cloud, and others are in preparation, e.g. a comprehensive investigation of classical Cepheids and a study of the proper motion in the foreground 47 Tuc cluster.

  10. SAGE-Var: An Infrared Survey of Variability in the Magellanic Clouds

    Science.gov (United States)

    Riebel, D.; Boyer, M. L.; Srinivasan, S.; Whitelock, P.; Meixner, M.; Babler, B.; Feast, M.; Groenewegen, M. A. T.; Ita, Y.; Meade, M.; Shiao, B.; Whitney, B.

    2015-07-01

    We present the first results from the Surveying the Agents of Galaxy Evolution (SAGE)-Var program, a follow up to the Spitzer legacy program SAGE (Meixner et al.). We obtained four epochs of photometry at 3.6 and 4.5 μm covering the bar of the LMC and the central region of the SMC in order to probe the variability of extremely red sources missed by variability surveys conducted at shorter wavelengths, and to provide additional epochs of observation for known variables. Our six total epochs of observations allow us to probe infrared (IR) variability on 15 different timescales ranging from ˜20 days to ˜5 yr. Out of a full catalog of 1 717 554 (LMC) and 457 760 (SMC) objects, we find 10 (LMC) and 6 (SMC) large amplitude Asymptotic Giant Branch (AGB) variables without optically measured variability owing to circumstellar dust obscuration. The catalog also contains multiple observations of known AGB variables, type I and II Cepheids, eclipsing variables, R CrB stars, and young stellar objects, which will be discussed in following papers. Here we present IR Period-Luminosity (PL) relations for classical Cepheids in the Magellanic Clouds, as well as improved PL relationships for AGB stars pulsating in the fundamental mode using mean magnitudes constructed from six epochs of observations.

  11. 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 ...

  12. Variable Stars in the Newly Discovered Milky Way Dwarf Spheroidal Satellite Canes Venatici I

    CERN Document Server

    Kuehn, Charles; Ripepi, Vincenzo; Clementini, Gisella; Dall'Ora, Massimo; Di Fabrizio, Luca; Rodgers, Christopher T; Greco, Claudia; Marconi, Marcella; Musella, Ilaria; Smith, Horace A; Catelan, Márcio; Beers, Timothy C; Pritzl, Barton J

    2007-01-01

    We have identified 23 RR Lyrae stars and 3 possible Anomalous Cepheids among 84 candidate variables in the recently discovered Canes Venatici I dwarf spheroidal galaxy. The mean period of 18 RRab type stars is = 0.60 +/-0.01 days. This period, and the location of these stars in the period-amplitude diagram, suggest that Canes Venatici I is likely an Oosterhoff-intermediate system. The average apparent magnitude of the RR Lyrae stars = 22.17 +/-0.02 is used to obtain a precision distance estimate of 210 +7/-5 kpc, for an adopted reddening E(B-V)=0.03 mag. We present a B,V color-magnitude diagram of Canes Venatici I that reaches V about 5 mag, and shows that the galaxy has a mainly old stellar population with a metal abundance near [Fe/H] = -2.0 dex. The width of the red giant branch and the location of the candidate Anomalous Cepheids on the color-magnitude diagram may indicate that the galaxy hosts a complex stellar population with stars from about 13 Gyr to as young as about 0.6 Gyr.

  13. 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.

    2016-08-01

    We present the identification of 634 variable stars in the Milky Way dSph satellite Sculptor based on archival ground-based optical observations spanning ˜24 years 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 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 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 (˜1.5M⊙) and SX Phoenicis stars (˜1M⊙). 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.

  14. Light curve demography via Bayesian functional data analysis

    Science.gov (United States)

    Loredo, Thomas; Budavari, Tamas; Hendry, Martin A.; Kowal, Daniel; Ruppert, David

    2015-08-01

    Synoptic time-domain surveys provide astronomers, not simply more data, but a different kind of data: large ensembles of multivariate, irregularly and asynchronously sampled light curves. We describe a statistical framework for light curve demography—optimal accumulation and extraction of information, not only along individual light curves as conventional methods do, but also across large ensembles of related light curves. We build the framework using tools from functional data analysis (FDA), a rapidly growing area of statistics that addresses inference from datasets that sample ensembles of related functions. Our Bayesian FDA framework builds hierarchical models that describe light curve ensembles using multiple levels of randomness: upper levels describe the source population, and lower levels describe the observation process, including measurement errors and selection effects. Schematically, a particular object's light curve is modeled as the sum of a parameterized template component (modeling population-averaged behavior) and a peculiar component (modeling variability across the population), subsequently subjected to an observation model. A functional shrinkage adjustment to individual light curves emerges—an adaptive, functional generalization of the kind of adjustments made for Eddington or Malmquist bias in single-epoch photometric surveys. We are applying the framework to a variety of problems in synoptic time-domain survey astronomy, including optimal detection of weak sources in multi-epoch data, and improved estimation of Cepheid variable star luminosities from detailed demographic modeling of ensembles of Cepheid light curves.

  15. 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...

  16. Galaxy distances and deviations from universal expansion; Proceedings of the NATO Advanced Research Workshop, Kona, HI, Jan. 13-17, 1986

    Science.gov (United States)

    Madore, Barry F. (Editor); Tully, R. Brent (Editor)

    1986-01-01

    A collection of papers on galaxy distances and deviations from universal expansion is presented. Individual topics addressed include: new results on the distance scale and the Hubble constant, Magellanic Clouds and the distance scale, CCD observations of Cepheids in nearby galaxies, distances using A supergiant stars, infrared calibration of the Cepheid distance scale, two stepping stones to the Hubble constant, physical models of supernovae and the distance scale, 21 cm line widths and distances of spiral galaxies, infrared color-luminosity relations for field galaxies, minimizing the scatter in the Tully-Fisher relation, photometry of galaxies and the local peculiar motion, elliptical galaxies and nonuniformities in the Hubble flow, and large-scale anisotropy in the Hubble flow. Also discussed are: improved distance indicator for elliptical galaxies, anisotropy of galaxies detected by IRAS, the local gravitational field, measurements of the CBR, measure of cosmological times, ages from nuclear cosmochronology, extragalactic gas at high redshift, supercluster infall models, Virgo infall and the mass density of the universe, dynamics of superclusters and Omega(0), distribution of galaxies versus dark matter, peculiar velocities and galaxy formation, cosmological shells and blast waves.

  17. Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388

    CERN Document Server

    Pritzl, B J; Catelan, M; Sweigart, A V; Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.

    2002-01-01

    We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6388 using time-series BV photometry. Twenty-eight new variables were found in this survey, increasing the total number of variables found near NGC 6388 to ~57. A significant number of the variables are RR Lyrae (~14), most of which are probable cluster members. The periods of the fundamental mode RR Lyrae are shown to be unusually long compared to metal-rich field stars. The existence of these long period RRab stars suggests that the horizontal branch of NGC 6388 is unusually bright. This implies that the metallicity-luminosity relationship for RR Lyrae stars is not universal if the RR Lyrae in NGC 6388 are indeed metal-rich. We consider the alternative possibility that the stars in NGC 6388 may span a range in [Fe/H]. Four candidate Population II Cepheids were also found. If they are members of the cluster, NGC 6388 would be the most metal-rich globular cluster to contain Population II Cepheids. The mean V magnitude of the...

  18. A new search for variable stars in the globular cluster NGC 6366

    CERN Document Server

    Ferro, A Arellano; Lopez, V Rojas; Figuera, R; Bramich, D M; Rosenzweig, P

    2008-01-01

    New CCD photometry of NGC 6366 has lead to the discovery of some variable stars. Two possible Anomalous Cepheids (or Pop II Cepheids), three long period variables, one SX Phe and one eclipsing binary have been found. Also a list of 10 candidate variables is reported. The light curve of the RRab star, V1, has been decomposed into its Fourier harmonics, and the Fourier parameters were used to estimate the star's metallicity and distance; [Fe/H] = -0.87 +- 0.14 and d = 3.2 +- 0.1 kpc. It is argued that V1 may not be a member of the cluster but rather a more distant object. If this is so, an upper limit for the distance to the cluster of 2.8 +- 0.1 kpc can be estimated. The P-L relationship for SX Phe stars and the identified modes in the newly discovered SX Phe variable, V6, allow yet another independent determination of the distance to the cluster of d = 2.7 \\+- 0.1 kpc. The M_V - {\\rm [Fe/H]} relationship for RR Lyrae stars is addressed and the case of V1 is discussed.

  19. Hubble Space Telescope Fine Guidance Sensor Interferometric Parallaxes; How, Why, and What

    Science.gov (United States)

    Benedict, George Frederick; McArthur, Barbara E.

    2015-08-01

    Over the past sixteen years the Fine Guidance Sensors on Hubble Space Telescope have produced astrometric measures with which to derive over 60 high-precision absolute parallaxes. Targets included the usual suspects (Cepheids and RR Lyr stars) as well as planetary nebulae central stars, dwarf novae, members of the Pleiades and Hyades clusters, M dwarf binaries, and exoplanet host stars. We briefly outline our techniques and summarize our results with four graphs: a Cepheid Leavitt Law, an RR Lyr K-band Period-Luminosity relation, an M dwarf Mass-Luminosity relation, and an MK vs (J-K)0 HR diagram constructed entirely with Hubble Space Telescope parallaxes. The median parallax error for 64 objects was 0.2 milliseconds of arc, or 2.6%.The future of Hubble Space Telescope astrometry likely lies with WFC spatial scanning. The far future of space astrometry lies with Gaia.FGS astrometry succeeded thanks to contributions over the years from L. Abramowicz-Reed, A. Bradley, R. Duncombe, O. Franz, L. Fredrick, P. Hemenway, T. Harrison, T. Henry, W. Jefferys, E. Nelan, P. Shelus, D. Story, W. van Altena, L. Wasserman, and A. Whipple.

  20. Constraints on stellar evolution from pulsations

    International Nuclear Information System (INIS)

    Consideration of the many types of intrinsic variable stars, that is, those that pulsate, reveals that perhaps a dozen classes can indicate some constraints that affect the results of stellar evolution calculations, or some interpretations of observations. Many of these constraints are not very strong or may not even be well defined yet. In this review we discuss only the case for six classes: classical Cepheids with their measured Wesselink radii, the observed surface effective temperatures of the known eleven double-mode Cepheids, the pulsation periods and measured surface effective temperatures of three R CrB variables, the delta Scuti variable VZ Cnc with a very large ratio of its two observed periods, the nonradial oscillations of our sun, and the period ratios of the newly discovered double-mode RR Lyrae variables. Unfortunately, the present state of knowledge about the exact compositions; mass loss and its dependence on the mass, radius, luminosity, and composition; ;and internal mixing processes, as well as sometimes the more basic parameters such as luminosities and surface effective temperatures prevent us from applying strong constraints for every case where currently the possibility exists

  1. 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....

  2. The Kep-Cont Mission: Continuing the observation of high-amplitude variable stars in the Kepler field of view

    CERN Document Server

    Molnár, L; Kolenberg, K; Borkovits, T; Antoci, V; Vida, K; Ngeow, C C; Guzik, J A; Plachy, E; Castanheira, B

    2013-01-01

    As a response to the Kepler white paper call, we propose to keep Kepler pointing to its current field of view and continue observing thousands of large amplitude variables (Cepheid, RR Lyrae and delta Scuti stars among others) with high cadence in the Kep-Cont Mission. The degraded pointing stability will still allow observation of these stars with reasonable (better than millimag) precision. The Kep-Cont mission will allow studying the nonradial modes in Blazhko-modulated and first overtone RR Lyrae stars and will give a better view on the period jitter of the only Kepler Cepheid in the field. With continued continuous observation of the Kepler RR Lyrae sample we may get closer to the origin of the century-old Blazhko problem. Longer time-span may also uncover new dynamical effects like apsidal motion in eclipsing binaries. A continued mission will have the advantage of providing unprecedented, many-years-long homogeneous and continuous photometric data of the same targets. We investigate the pragmatic detai...

  3. Precise Radial Velocities of Polaris: Detection of Amplitude Growth

    CERN Document Server

    Lee, Byeong-Cheol; Han, Inwoo; Park, Myeong-Gu; Kim, Kang-Min

    2008-01-01

    We present a first results from a long-term program of a radial velocity study of Cepheid Polaris (F7 Ib) aimed to find amplitude and period of pulsations and nature of secondary periodicities. 264 new precise radial velocity measurements were obtained during 2004-2007 with the fiber-fed echelle spectrograph Bohyunsan Observatory Echelle Spectrograph (BOES) of 1.8m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We find a pulsational radial velocity amplitude and period of Polaris for three seasons of 2005.183, 2006.360, and 2007.349 as 2K = 2.210 +/- 0.048 km/s, 2K = 2.080 +/- 0.042 km/s, and 2K = 2.406 +/- 0.018 km/s respectively, indicating that the pulsational amplitudes of Polaris that had decayed during the last century is now increasing rapidly. The pulsational period was found to be increasing too. This is the first detection of a historical turnaround of pulsational amplitude change in Cepheids. We clearly find the presence of additional radial velocity variations on a time scal...

  4. MACHO project 9 million star color-magnitude diagram of the large magellanic cloud

    Energy Technology Data Exchange (ETDEWEB)

    Alcock, C; Allsman, R A; Alves, D R; Axelrod, T S; Basu, A; Becker, A C; Bennett, D P; Cook, K H; Drake, A J; Freeman, K C; Geha, M; Griest, K; King,L; Lehner, M J; Marshall, S L; Minniti, D; Nelson, C; Peterson, B A; Popowski, P; Pratt, M R; Quinn, P J; Stubbs, C W; Sutherland, W.; Tomaney, A B; Vandehei, T.; Welch, D L

    2000-01-31

    The authors present a 9 million star color-magnitude diagram (9M CMD) of the Large Magellanic Cloud (LMC) bar. The 9M CMD reveals a complex superposition of different age and metallicity stellar populations, with important stellar evolutionary phases occurring over three orders of magnitude in number density. First, they count the non-variable red and blue supergiants, the associated Cepheid variables, and measure the stellar effective temperatures defining the Cepheid instability strip. Lifetime predictions of stellar evolution theory are tested, with implications for the origin of low-luminosity Cepheids. The highly-evolved asymptotic giant branch (AGB) stars in the 9M CMD have a bimodal distribution in brightness, which they interpret as discrete old populations ({ge} 1 Gyr). The faint AGB sequence may be metal-poor and very old. Comparing the mean properties of giant branch and horizontal branch (HB) stars in the 9M CMD to those of clusters, they identify NGC 411 and M3 as templates for the admixture of old stellar populations in the bar. However, there are several indications that the old and metal-poor field population has a red HB morphology: the RR Lyrae variables lie preferentially on the red edge of the instability strip, the AGB-bump is very red, and the ratio of AGB-bump stars to RR Lyraes is quite large. If the HB second parameter is age, the old and metal-poor field population in the bar likely formed after the oldest LMC clusters. Lifetime predictions of stellar evolution theory lead us to associate a significant fraction of the {approx} 1 million red HB clump giants in the 9M CMD with the same old and metal-poor population producing the RR Lyraes and the AGB-bump. In this case, compared to the age-dependent luminosity predictions of stellar evolution theory, the red HB clump is too bright relative to the RR Lyraes and AGB-bump. Last, they show that the surface density profile of RR Lyraes is fit by an exponential, favoring a disk-like rather than

  5. 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.

  6. 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.

  7. A supernova distance to the anchor galaxy NGC 4258

    CERN Document Server

    Polshaw, J; Chambers, K C; Smartt, S J; Taubenberger, S; Kromer, M; Gall, E E E; Hillebrandt, W; Huber, M; Smith, K W; Wainscoat, R J

    2015-01-01

    The fortuitous occurrence of a type II-Plateau (IIP) supernova, SN~2014bc, in a galaxy for which distance estimates from a number of primary distance indicators are available provides a means with which to cross-calibrate the standardised candle method (SCM) for type IIP SNe. By applying calibrations from the literature we find distance estimates in line with the most precise measurement to NGC~4258 based on the Keplerian motion of masers (7.6$\\pm$0.23\\,Mpc), albeit with significant scatter. We provide an alternative local SCM calibration by only considering type IIP SNe that have occurred in galaxies for which a Cepheid distance estimate is available. We find a considerable reduction in scatter ($\\sigma_I = 0.16$\\, mag.), but note that the current sample size is limited. Applying this calibration, we estimate a distance to NGC~4258 of $7.08\\pm0.86$ Mpc.

  8. Detailed HI kinematics of Tully-Fisher calibrator galaxies

    CERN Document Server

    Ponomareva, Anastasia A; Bosma, Albert

    2016-01-01

    We present spatially-resolved HI kinematics of 32 spiral galaxies which have Cepheid or/and Tip of the Red Giant Branch distances, and define a calibrator sample for the Tully-Fisher relation. The interferometric HI data for this sample were collected from available archives and supplemented with new GMRT observations. This paper describes an uniform analysis of the HI kinematics of this inhomogeneous data set. Our main result is an atlas for our calibrator sample that presents global HI profiles, integrated HI column-density maps, HI surface density profiles and, most importantly, detailed kinematic information in the form of high-quality rotation curves derived from highly-resolved, two-dimensional velocity fields and position-velocity diagrams.

  9. False positivity of Serological tests for hepatitis C virus

    International Nuclear Information System (INIS)

    Background: Hepatitis C virus infection is now one the common infection in Pakistan. Patients are routinely screened by antibody assays. Objective of this study was to assess the viremia in patients labelled as anti-HCV positive by ELISA. Methods: It this retrospective study patients labelled as anti HCV positive by ELISA were assessed for HCV RNA by polymerase chain reaction. The 254 HCV positive cases which were analysed by MEIA method on AxSYM System were selected for RNA extraction by RT-PCR upon Cepheid thermal cycler using TaqMan technology and subsequent for amplification. Results: Out of 254 anti HCV positive by ELISA, viremia was shown in 211 patients; the remaining 43 (16.92%) samples were false positive. Conclusion: Out of a total 254 anti HCV positive patients, 211 had viremia by RT-PCR. The false positivity noted was 16.9%. (author)

  10. Evaluation of the Xpert Flu test and comparison with in-house real-time RT-PCR assays for detection of influenza virus from 2008 to 2011 in Marseille, France.

    Science.gov (United States)

    Salez, N; Ninove, L; Thirion, L; Gazin, C; Zandotti, C; de Lamballerie, X; Charrel, R N

    2012-04-01

    Rapid documentation of respiratory specimens can have an impact on the management of patients and their relatives in terms of preventive and curative measures. We compared the results of the Xpert(®) Flu assay (Cepheid) with three real-time RT-PCR assays using 127 nasopharyngeal samples, of which 75 were positive for influenza A (with 52 identified as A/H1N1-2009) and 52 were positive for influenza B. The Xpert(®) Flu assay presented a quasi-absence of non-interpretable tests, and showed sensitivity and specificity of 100% and 100% for Flu A, 98.4% and 100% for A/H1N1-2009, and 80.7% and 100% for Flu B. PMID:22360446

  11. Xpert Flu for point-of-care diagnosis of human influenza in industrialized countries.

    Science.gov (United States)

    Salez, Nicolas; Nougairede, Antoine; Ninove, Laetitia; Zandotti, Christine; de Lamballerie, Xavier; Charrel, Rémi N

    2014-05-01

    Respiratory infections, particularly those caused by influenza viruses, represent the third-most important cause of death in the world due to infectious diseases. Nevertheless, despite the enormous publicity attracted by epidemics due to these viruses, laboratory diagnosis, documentation and recording of respiratory diseases is still unsatisfactory. Available diagnostic tests capable of providing results rapidly are either limited and insufficiently sensitive or highly sensitive and specific but insufficiently rapid. Considerable investment and research efforts have been made towards the development of new diagnostics for influenza A and B viruses and the Xpert(®) Flu assay (Cepheid(®), CA, USA) has emerged as one of the most promising. In this article, we review current knowledge of the Xpert Flu test, discuss its potential value as a point-of-care test and outline the potential leads for future development. PMID:24707995

  12. Gamma-Ray Bursts as Cosmological Tools

    CERN Document Server

    Petrosian, Vahe; Ryde, Felix

    2009-01-01

    In recent years there has been considerable activity in using gamma-ray bursts as cosmological probes for determining global cosmological parameters complementing results from type Ia supernovae and other methods. This requires a characteristics of the source to be a standard candle. We show that contrary to earlier indications the accumulated data speak against this possibility. Another method would be to use correlation between a distance dependent and a distance independent variable to measure distance and determine cosmological parameters as is done using Cepheid variables and to some extent Type Ia supernovae. Many papers have dealt with the use of so called Amati relation, first predicted by Lloyd, Petrosian and Mallozzi, or the Ghirlanda relation for this purpose. We have argued that these procedure involve many unjustified assumptions which if not true could invalidate the results. In particular, we point out that many evolutionary effects can affect the final outcome. In particular, we demonstrate th...

  13. Constructing a cosmological model-independent Hubble diagram of type Ia supernovae with cosmic chronometers

    CERN Document Server

    Li, Zhengxiang; Yu, Hongwei; Zhu, Zong-Hong; Alcaniz, J S

    2015-01-01

    We apply two methods to reconstruct the Hubble parameter $H(z)$ as a function of redshift from 15 measurements of the expansion rate obtained from age estimates of passively evolving galaxies. These reconstructions enable us to derive the luminosity distance to a certain redshift $z$, calibrate the light-curve fitting parameters accounting for the (unknown) intrinsic magnitude of type Ia supernova (SNe Ia) and construct cosmological model-independent Hubble diagrams of SNe Ia. In order to test the compatibility between the reconstructed functions of $H(z)$, we perform a statistical analysis considering the latest SNe Ia sample, the so-called JLA compilation. We find that, while one of the reconstructed functions leads to a value of the local Hubble parameter $H_0$ in excellent agreement with the one reported by the Planck collaboration, the other requires a higher value of $H_0$, which is consistent with recent measurements of this quantity from Cepheids and other local distance indicators.

  14. On the metallicity of open clusters. III. Homogenised sample

    CERN Document Server

    Netopil, M; Heiter, U; Soubiran, C

    2016-01-01

    Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. W...

  15. Spectroscopic studies of yellow supergiants in the open cluster NGC 129

    Science.gov (United States)

    Usenko, I. A.

    2015-09-01

    Spectroscopic studies of three yellow supergiants in the open cluster NGC 129, the classical Cepheid DL Cas, SAO 21450, and SAO 21482, have been performed on the basis of high-resolution spectra. For the two nonvariable cluster supergiants, the atmospheric parameters and chemical composition have been determined for the first time. SAO 21450 ( T eff = 6541 ± 16 K, log g = 2.00, V t = 4.20 km s-1) has nearly solar abundances of the key elements in the evolution of yellow supergiants (CNO, Na, Mg, and Al), while SAO 21482 ( T eff = 4506 ± 50 K, log g = 1.10, V t = 9.90 km s-1) exhibits an overabundance of carbon ([C/H] = +0.34 dex) and aluminum and nearly solar N, O, Na, and Mg abundances. The abundances of the key elements in the Cepheid DL Cas are typical for an object that has passed the first dredge-up: a C underabundance, N and Na overabundances, and nearly solar O, Mg, and Al abundances. In all objects, the abundances of iron [Fe/H] = -0.01 dex, α-elements, Fe-peak elements, and r- and s-process elements are virtually identical and nearly solar. The radial velocities of SAO 21482 measured from metal absorption lines have confirmed its membership in NGC 129. The knifelike shape of the H α and H β line profiles in SAO 21482 and the asymmetry of the Mg Ib 5183.618 Å line in SAO 21482 and DL Cas as well as the absorption lines of neutral atoms and ions of metals in the Cepheid suggest the existence of extended gaseous envelopes around them. The positions of the objects on the T eff- L diagram among the tracks of evolutionary masses for the objects show the following: (1) the primary component of SAO 21450 has a mass of 6.6 M ⊙ and approaches the blue edge of the Cepheid instability strip (CIS) for the first time, while its companion of possible spectral type B5 V has a mass of 4.8 M ⊙; (2) DL Cas is on the path of its CIS with a mass of 5.8 M ⊙ and has lost ~1.5 M ⊙ after the first dredge-up; (3) SAO 21482 with a mass of no more than 7.3 M ⊙ has

  16. A New Distance to M33 Using Blue Supergiants and the FGLR Method

    CERN Document Server

    U, Vivian; Kudritzki, Rolf-Peter; Jacobs, Bradley A; Bresolin, Fabio; Przybilla, Norbert

    2009-01-01

    The quantitative spectral analysis of medium resolution optical spectra of A and B supergiants obtained with DEIMOS and ESI at the Keck Telescopes is used to determine a distance modulus of 24.93 +/- 0.11 mag for the Triangulum Galaxy M33. The analysis yields stellar effective temperatures, gravities, interstellar reddening, and extinction, the combination of which provides a distance estimate via the Flux-weighted Gravity--Luminosity Relationship (FGLR). This result is based on an FGLR calibration that is continually being polished. An average reddening of ~ 0.08 mag is found, with a large variation ranging from 0.01 to 0.16 mag however, demonstrating the importance of accurate individual reddening measurements for stellar distance indicators in galaxies with evident signatures of interstellar absorption. The large distance modulus found is in good agreement with recent work on eclipsing binaries, planetary nebulae, long period variables, RR Lyrae stars, and also with HST observations of Cepheids, if reason...

  17. Looking for New Cataclysmic Variables

    Science.gov (United States)

    Steiner, J. E.; Cieslinski, D.; Jablonski, F. J.

    1987-05-01

    ABSTRACT. One year ago we have started a program of observations of southern irregular variables of the types L, I and I , selected from the catalogs GCVS and NSV. The goal is to identify new cataclysmic variables and related objects. So far we have done photoelectric photometry of about 350 objects and spectroscopy of 120 of them. Nearly 80% of all observed objects are red giant-like. The other 20% comprise a large variety of types such as T Tauri, Mirae, Cepheids, Planetary Nebulae, etc. Ten new cataclysmic variables and one x-ray binary were also identified. Some of these objects studied in more detail, show interesting behavior. Key o : PHOTOMETRY -- SPECTROSCOPY -- VARIABLES

  18. Point-of-Care Diagnosis of Tuberculosis - Past, Present and Future

    DEFF Research Database (Denmark)

    Dheda, Keertan; Ruhwald, Morten; Theron, Grant;

    2013-01-01

    -day results at point-of-care (POC). When a return visit is required to access test results, time to treatment is prolonged and default rates are significant. However, a good diagnostic tool is also critically dependent on obtaining an adequate biological sample. Here we review the accuracy and potential...... impact of established and newer potential POC diagnostic tests for TB including smear microscopy, the Xpert MTB/RIF assay (Cepheid) and the Determine TB LAM antigen test (Alere). Novel experimental approaches and detection technologies for POC diagnosis of active TB, including nucleic acid amplification...... tests, detection of volatile organic compounds or metabolites, mass spectroscopy, microfluidics, SERS, electrochemical approaches, and aptamers amongst others, are discussed. We also discuss future applications, including the potential POC diagnosis of drug-resistant TB and presumed latent TB infection...

  19. Reddening, Abundances, and Line Formation in SNe II

    CERN Document Server

    Baron, E; Hauschildt, P H; Branch, David; Hauschildt, Peter H.

    2007-01-01

    We present detailed NLTE spectral synthesis models of the Type II supernova 2005cs, which occurred in M51 and for which the explosion time is well determined. We show that previous estimates for the reddening were significantly too high and briefly discuss how this will effect the inferred progenitor mass. We also show that standard CNO-burning enhanced abundances require far too large an oxygen depletion, although there is evidence for a single optical N II line and the sodium abundance shows clear evidence for enhancement over solar both as expected from CNO processing. Finally we calculate a distance using the SEAM method. Given the broad range of distances to M51 in the literature, the determination of a distance using Cepheid variables would be quite valuable.

  20. Chaos in the Music of the Spheres

    CERN Document Server

    Buchler, J R; Cadmus, R; Kollath, Zoltan; Cadmus, Robert

    2001-01-01

    The light curves (time series of the radiated energy) of most large amplitude, pulsating stars such as the well known Cepheid stars are regular. However, a smaller group of variable stars that are located next to them in the Hertzsprung- Russell diagram undergoes irregular light variations and exhibits irregular radial velocities as well. The mechanism behind this irregular behavior was a long standing mystery. A flow reconstruction technique based on the observed lightcurves of six separate stars shows that their underlying dynamics is chaotic and low dimensional (d=4). Furthermore, we present evidence that the physical mechanism behind the behavior is the nonlinear interaction of just two pulsation eigenmodes. In a generalized Shil'nikov scenario, the pulsation energy alternates continuously, but irregularly between a lower frequency mode that is linearly unstable and thus growing, and a stable overtone that gets entrained through a low order resonance (2:1), but that wants to decay. The flow reconstruction...

  1. Analysis of photometric uncertainties in the OGLE-IV Galactic Bulge microlensing survey data

    CERN Document Server

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

    2016-01-01

    We present a statistical assessment of both, observed and reported, photometric uncertainties in the OGLE-IV Galactic bulge microlensing survey data. This dataset is widely used for the detection of variable stars, transient objects, discovery of microlensing events, and characterization of the exo-planetary systems. Large collections of RR Lyrae stars and Cepheids discovered by the OGLE project toward the Galactic bulge provide light curves based on this dataset. We describe the method of analysis, and provide the procedure, which can be used to update preliminary photometric uncertainties, provided with the light curves, to the ones reflecting the actual observed scatter at a given magnitude and for a given CCD detector of the OGLE-IV camera.This is of key importance for data modeling, in particular, for the correct estimation of the goodness of fit.

  2. Evaluation of 3 automated real-time PCR (Xpert C. difficile assay, BD MAX Cdiff, and IMDx C. difficile for Abbott m2000 assay) for detecting Clostridium difficile toxin gene compared to toxigenic culture in stool specimens.

    Science.gov (United States)

    Yoo, Jaeeun; Lee, Hyeyoung; Park, Kang Gyun; Lee, Gun Dong; Park, Yong Gyu; Park, Yeon-Joon

    2015-09-01

    We evaluated the performance of the 3 automated systems (Cepheid Xpert, BD MAX, and IMDx C. difficile for Abbott m2000) detecting Clostridium difficile toxin gene compared to toxigenic culture. Of the 254 stool specimens tested, 87 (48 slight, 35 moderate, and 4 heavy growth) were toxigenic culture positive. The overall sensitivities and specificities were 82.8% and 98.8% for Xpert, 81.6% and 95.8% for BD MAX, and 62.1% and 99.4% for IMDx, respectively. The specificity was significantly higher in IMDx than BD MAX (P= 0.03). All stool samples underwent toxin A/B enzyme immunoassay testing, and of the 254 samples, only 29 samples were positive and 2 of them were toxigenic culture negative. Considering the rapidity and high specificity of the real-time PCR assays compared to the toxigenic culture, they can be used as the first test method for C. difficile infection/colonization. PMID:26081240

  3. The RCB star RY Sagittarii as a pulsating star

    Science.gov (United States)

    Lloyd Evans, T.

    1986-03-01

    Measurements of CN and C2 bandstrengths in the spectrum of RY Sagittarii in 1969 and 1970, when it was on the latter part of its return to maximum and during its subsequent stay at maximum light after the deep minimum of 1967-68, show that the bands vary in strength in the 38.6-day pulsation period. The variations follow the phasing of the B-V and U-B color curves rather than the V light curve, and must be determined largely by the photospheric temperature as in the case of the carbon-rich Cepheid V553 Centauri. This is supported by a comparison of the ranges in color and in bandstrength, though the bands are stronger at a given color than in typical class Ib supergiants.

  4. The Carnegie-Chicago Hubble Program. I. A New Approach to the Distance Ladder Using Only Distance Indicators of Population II

    CERN Document Server

    Beaton, Rachael L; Madore, Barry F; Bono, Giuseppe; Carlson, Erika K; Clementini, Gisella; Durbin, Meredith J; Garofalo, Alessia; Hatt, Dylan; Jang, In Sung; Lee, Myung Gyoon; Monson, Andrew J; Rich, Jeffrey A; Scowcroft, Victoria; Seibert, Mark; Sturch, Laura; Yang, Soung-Chul

    2016-01-01

    We present an overview of the Carnegie-Chicago Hubble Program, an ongoing program to obtain a 3 per cent measurement of the Hubble constant using alternative methods to the traditional Cepheid distance scale. We aim to establish a completely independent route to the Hubble constant using RR Lyrae variables, the tip of the red giant branch (TRGB), and Type Ia supernovae (SNe Ia). This alternative distance ladder can be applied to galaxies of any Hubble Type, of any inclination, and, utilizing old stars in low density environments, is robust to the degenerate effects of metallicity and interstellar extinction. Given the relatively small number of SNe Ia host galaxies with independently measured distances, these properties provide a great systematic advantage in the measurement of the Hubble constant via the distance ladder. Initially, the accuracy of our value of the Hubble constant will be set by the five Galactic RR Lyrae calibrators with Hubble Space Telescope Fine-Guidance Sensor parallaxes. With Gaia, both...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-01

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

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

    International Nuclear Information System (INIS)

    The Taiwanese-American Occultation Survey project is designed for the detection of stellar occultations by small-size Kuiper Belt Objects, and it has monitored selected fields along the ecliptic plane by using four telescopes with a 3 deg2 field of view on the sky since 2005. We have analyzed data accumulated during 2005-2012 to detect variable stars. Sixteen fields with observations of more than 100 epochs were examined. We recovered 85 variables among a total of 158 known variable stars in these 16 fields. Most of the unrecovered variables are located in the fields observed less frequently. We also detected 58 variable stars which are not listed in the International Variable Star Index of the American Association of Variable Star Observers. These variable stars are classified as 3 RR Lyrae, 4 Cepheid, 1 δ Scuti, 5 Mira, 15 semi-regular, and 27 eclipsing binaries based on the periodicity and the profile of the light curves.

  7. Variable stars from the OGLE survey

    Science.gov (United States)

    Soszyński, I.; Udalski, A.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Wyrzykowski, &Lslash; .; Ulaczyk, K.; Poleski, R.; Koz&lslash; owski, S.; Pietrukowicz, P.; Skowron, J.

    Variable stars have long been recognized as excellent tracers of stellar populations. Large and complete samples of variable stars allow to study the spatial distribution of stellar populations of given ages, provide important clues to the star formation history, put constraints on stellar physical properties, and are used to determine distances. We would like to present a unique compilation of variable stars obtained from the long-term observations collected in the course of the Optical Gravitational Lensing Experiment (OGLE). Huge samples of classical, type II and anomalous Cepheids, RR Lyrae stars, long-period variables and other types of variable stars have been discovered in the Magellanic Clouds and in the Galactic bulge. We would also like to present first results from the fourth phase of the OGLE project (OGLE-IV) - a spatial distribution of variable stars in the wide region covering the Magellanic Clouds and the Magellanic Bridge connecting both galaxies.

  8. Cosmology and the Hubble Constant: On the Megamaser Cosmology Project (MCP)

    CERN Document Server

    Henkel, C; Reid, M J; Condon, J J; Lo, K Y; Impellizzeri, C M V; Kuo, C Y

    2012-01-01

    The Hubble constant Ho describes not only the expansion of local space at redshift z ~ 0, but is also a fundamental parameter determining the evolution of the universe. Recent measurements of Ho anchored on Cepheid observations have reached a precision of several percent. However, this problem is so important that confirmation from several methods is needed to better constrain Ho and, with it, dark energy and the curvature of space. A particularly direct method involves the determination of distances to local galaxies far enough to be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear supermassive black holes. The goal of this article is to describe the relevance of Ho with respect to fundamental cosmological questions and to summarize recent progress of the the `Megamaser Cosmology Project' (MCP) related to the Hubble constant.

  9. New Variable Stars on Digitized Moscow Collection Plates. Field 66 Ophiuchi (Northern Half)

    CERN Document Server

    Kolesnikova, D M; Sokolovsky, K V; Antipin, S V; Samus, N N

    2008-01-01

    We initiated digitization of the Moscow collection of astronomical plates using flatbed scanners. Techniques of photographic photometry of the digital images were applied, enabling an effective search for new variable stars. Our search for new variables among 140000 stars in the 10 x 5 degrees northern half of the field centered at 66 Oph, photographed with the Sternberg Institute's 40-cm astrograph in 1976--1995, gave 274 new discoveries, among them: 2 probable Population II Cepheids; 81 eclipsing variables; 5 high-amplitude Delta Scuti stars (HADSs); 82 RR Lyr stars; 62 red irregular variables and 41 red semiregular stars; 1 slow irregular variable not red in color. Light elements were determined for periodic variable stars. We detected about 30 variability suspects for follow-up CCD observations, confirmed 11 stars from the New Catalogue of Suspected Variable Stars, and derived new light elements for 2stars already contained in the General Catalogue of Variable Stars.

  10. An Analytic Mathematical Model to Explain the Spiral Structure and Rotation Curve of NGC 3198

    Science.gov (United States)

    Rout, Bruce; Rout, Cameron

    2016-06-01

    An analytical model of galactic morphology is presented. This model presents resolutions to two inter-related parameters of spiral galaxies: one being the flat velocity rotation profile and the other being the spiral morphology of such galaxies. This model is a mathematical transformation dictated by the general theory of relativity applied to rotating polar coordinate systems that conserve the metric. The model shows that the flat velocity rotation profile and spiral shape of certain galaxies are both products of the general theory. Validation of the model is presented by application to 878 rotation curves provided by Salucci, and by comparing the results of a derived distance modulus to those using Cepheid variables, water masers and Tully-Fisher calculations. The model suggests means of determining galactic linear density, mass and angular momentum. We also show that the morphology of NGC 3198 is congruent to the geodesic as observed within a rotating reference frame and that galaxies are gravitationally viscous and self bound.

  11. Testing Distance Estimators with the Fundamental Manifold

    CERN Document Server

    Zaritsky, Dennis; Gonzalez, Anthony H

    2012-01-01

    We demonstrate how the Fundamental Manifold (FM) can be used to cross-calibrate distance estimators even when those "standard candles" are not found in the same galaxy. Such an approach greatly increases the number of distance measurements that can be utilized to check for systematic distance errors and the types of estimators that can be compared. Here we compare distances obtained using SN Ia, Cepheids, surface brightness fluctuations, the luminosity of the tip of the red giant branch, circumnuclear masers, eclipsing binaries, RR Lyrae stars, and the planetary nebulae luminosity functions. We find no significant discrepancies (differences are < 2 sigma) between distance methods, although differences at the ~10% level cannot yet be ruled out. The potential exists for significant refinement because the data used here are heterogeneous B-band magnitudes that will soon be supplanted by homogeneous, near-IR magnitudes. We illustrate the use of FM distances to 1) revisit the question of the metallicity sensiti...

  12. Variable Stars in the Field of the Hydra II Ultra-Faint Dwarf Galaxy

    Science.gov (United States)

    Vivas, Anna Katherina; Olsen, Knut A.; Blum, Robert D.; Nidever, David L.; Walker, Alistair R.; Martin, Nicolas; Besla, Gurtina; Gallart, Carme; Van Der Marel, Roeland P.; Majewski, Steven R.; Munoz, Ricardo; Kaleida, Catherine C.; Saha, Abhijit; Conn, Blair; Jin, Shoko

    2016-06-01

    We searched for variable stars in Hydra II, one of the recently discovered ultra-faint dwarf satellites of the Milky Way, using gri time-series obtained with the Dark Energy Camera (DECam) at Cerro Tololo Inter-American Observatory, Chile. We discovered one RR Lyrae star in the galaxy which was used to derive a distance of 154±8 kpc to this system and to re-calculate its absolute magnitude and half-light radius.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.

  13. Spectroscopic studies of four southern-hemisphere G-K supergiants: HD 192876 (α1 Cap), HD 194215 (HR 7801), HD 206834 (c Cap), and HD 222574 (104 Aqr)

    Science.gov (United States)

    Usenko, I. A.; Kniazev, A. Yu.; Berdnikov, L. N.; Kravtsov, V. V.

    2015-11-01

    We have studied the high-resolution spectra taken with the 1.9-m telescope of the South African Astronomical Observatory for four supergiants that are deemed to be nonvariable and to lie beyond the red edge of the Cepheid instability strip (CIS): HD 192876, HD 194215, HD 206834, and HD 222574. The atmospheric parameters, reddenings, luminosities, distances, radii, and chemical composition have been determined for these stars. Based on these results, we have ascertained thatHD194215 is not a mainsequence star but an ordinary supergiant. All objects exhibit a nearly solar metallicity. The abundances of carbon and oxygen in HD 194215 and HD 206834 are nearly solar, while they are underabundant in HD 192876 and HD 222574. The abundances of sodium, magnesium, and aluminum are different for all objects, while those of the remaining elements are nearly solar. For HD 206834, the measured radial velocity exceeds its previously known values by a factor of 3, while the asymmetric knifelike profiles of the Ha and Hß absorption lines suggest the existence of an extended envelope around the star. Similar profiles of hydrogen absorption lines and strong lines of some metals with low lower-level excitation potentials have also been revealed in the spectrum of HD 222574. The positions of the supergiants on the effective temperature-luminosity diagram in comparison with the evolutionary tracks of the stars have shown their masses to lie within the range 3.4-4.3 M ⊙. HD 194215 and HD 206834 have crossed the CIS for the first time, with the latter object being near the stage of transformation into a red supergiant. HD 192876 and HD 222574 have already passed the first dredge-up and probably move from right to left, crossing the CIS for the second time. The position of HD 222574 near the red CIS edge is probably attributable to its Cepheid-like brightness and radial velocity variations.

  14. Community College Class Devoted to Astronomical Research

    Science.gov (United States)

    Genet, R. M.; Genet, C. L.

    2002-05-01

    A class at a small community college, Central Arizona College, was dedicated to astronomical research. Although hands-on research is usually reserved for professionals or graduate students, and occasionally individual undergraduate seniors, we decided to introduce community college students to science by devoting an entire class to research. Nine students were formed into three closely cooperating teams. The class as a whole decided that all three teams would observe Cepheid stars photometrically using a robotic telescope at the Fairborn Observatory. Speaker-phone conference calls were made to Kenneth E. Kissell for help on Cepheid selection, Michael A. Seeds for instructions on the use of the Phoenix-10 robotic telescope, and Douglas S. Hall for assitance in selecting appropriate comparison and check stars. The students obtained critical references on past observations from Konkoly Observatory via airmail. They spent several long night sessions at our apartment compiling the data, making phase calculations, and creating graphs. Finally, the students wrote up their results for publication in a forthcoming special issue of the international journal on stellar photometry, the IAPPP Communication. We concluded that conducting team research is an excellent way to introduce community college students to science, that a class devoted to cooperation as opposed to competition was refreshing, and that group student conference calls with working astronomers were inspiring. A semester, however, is a rather short time to initiate and complete research projects. The students were Sally Baldwin, Cory Bushnell, Bryan Dehart, Pamela Frantz, Carl Fugate, Mike Grill, Jessica Harger, Klay Lapa, and Diane Wiseman. We are pleased to acknowledge the assistance provided by the astronomers mentioned above, James Stuckey (Campus Dean), and our Union Institute and University doctoral committee members Florence Pittman Matusky, Donald S. Hayes, and Karen S. Grove.

  15. NEW EVIDENCE FOR MASS LOSS FROM δ CEPHEI FROM H I 21 cm LINE OBSERVATIONS

    International Nuclear Information System (INIS)

    Recently published Spitzer Space Telescope observations of the classical Cepheid archetype δ Cephei revealed an extended dusty nebula surrounding this star and its hot companion HD 213307. At far-infrared wavelengths, the emission resembles a bow shock aligned with the direction of space motion of the star, indicating that δ Cephei is undergoing mass loss through a stellar wind. Here we report H I 21 cm line observations with the Very Large Array (VLA) to search for neutral atomic hydrogen associated with this wind. Our VLA data reveal a spatially extended H I nebula (∼13' or 1 pc across) surrounding the position of δ Cephei. The nebula has a head-tail morphology, consistent with circumstellar ejecta shaped by the interaction between a stellar wind and the interstellar medium (ISM). We directly measure a mass of circumstellar atomic hydrogen MHi∼0.07 Msun, although the total H I mass may be larger, depending on the fraction of circumstellar material that is hidden by Galactic contamination within our band or that is present on angular scales too large to be detected by the VLA. It appears that the bulk of the circumstellar gas has originated directly from the star, although it may be augmented by material swept from the surrounding ISM. The H I data are consistent with a stellar wind with an outflow velocity Vo = 35.6 ± 1.2 km s–1 and a mass-loss rate of M-dot ∼(1.0±0.8)×10-6 Msun yr–1. We have computed theoretical evolutionary tracks that include mass loss across the instability strip and show that a mass-loss rate of this magnitude, sustained over the preceding Cepheid lifetime of δ Cephei, could be sufficient to resolve a significant fraction of the discrepancy between the pulsation and evolutionary masses for this star.

  16. HIDE AND SEEK BETWEEN ANDROMEDA'S HALO, DISK, AND GIANT STREAM

    International Nuclear Information System (INIS)

    Photometry in B, V (down to V ∼ 26 mag) is presented for two 23' × 23' fields of the Andromeda galaxy (M31) that were observed with the blue channel camera of the Large Binocular Telescope during the Science Demonstration Time. Each field covers an area of about 5.1 × 5.1 kpc2 at the distance of M31 (μM31 ∼ 24.4 mag), sampling, respectively, a northeast region close to the M31 giant stream (field S2) and an eastern portion of the halo in the direction of the galaxy minor axis (field H1). The stream field spans a region that includes Andromeda's disk and giant stream, and this is reflected in the complexity of the color-magnitude diagram of the field. One corner of the halo field also includes a portion of the giant stream. Even though these demonstration time data were obtained under non-optimal observing conditions, the B photometry, which was acquired in time-series mode, allowed us to identify 274 variable stars (among which 96 are bona fide and 31 are candidate RR Lyrae stars, 71 are Cepheids, and 16 are binary systems) by applying the image subtraction technique to the selected portions of the observed fields. Differential flux light curves were obtained for the vast majority of these variables. Our sample mainly includes pulsating stars that populate the instability strip from the Classical Cepheids down to the RR Lyrae stars, thus tracing the different stellar generations in these regions of M31 down to the horizontal branch of the oldest (t ∼ 10 Gyr) component.

  17. HIDE AND SEEK BETWEEN ANDROMEDA'S HALO, DISK, AND GIANT STREAM

    Energy Technology Data Exchange (ETDEWEB)

    Clementini, Gisella; Contreras Ramos, Rodrigo; Federici, Luciana; Macario, Giulia; Tosi, Monica; Bellazzini, Michele; Fusi Pecci, Flavio; Diolaiti, Emiliano; Cacciari, Carla [INAF, Osservatorio Astronomico di Bologna, Bologna (Italy); Beccari, Giacomo [European Southern Observatory, 85748 Garching bei Munchen (Germany); Testa, Vincenzo; Giallongo, Emanuele; Di Paola, Andrea; Gallozzi, Stefano [INAF, Osservatorio Astronomico di Roma, Monteporzio (Italy); Cignoni, Michele; Marano, Bruno [Dipartimento di Astronomia, Universita di Bologna, Bologna (Italy); Marconi, Marcella; Ripepi, Vincenzo [INAF, Osservatorio Astronomico di Capodimonte, Napoli (Italy); Ragazzoni, Roberto [INAF, Osservatorio Astronomico di Padova, Padova (Italy); Smareglia, Riccardo, E-mail: gisella.clementini@oabo.inaf.it [INAF, Osservatorio Astronomico di Trieste, Trieste (Italy)

    2011-12-10

    Photometry in B, V (down to V {approx} 26 mag) is presented for two 23' Multiplication-Sign 23' fields of the Andromeda galaxy (M31) that were observed with the blue channel camera of the Large Binocular Telescope during the Science Demonstration Time. Each field covers an area of about 5.1 Multiplication-Sign 5.1 kpc{sup 2} at the distance of M31 ({mu}{sub M31} {approx} 24.4 mag), sampling, respectively, a northeast region close to the M31 giant stream (field S2) and an eastern portion of the halo in the direction of the galaxy minor axis (field H1). The stream field spans a region that includes Andromeda's disk and giant stream, and this is reflected in the complexity of the color-magnitude diagram of the field. One corner of the halo field also includes a portion of the giant stream. Even though these demonstration time data were obtained under non-optimal observing conditions, the B photometry, which was acquired in time-series mode, allowed us to identify 274 variable stars (among which 96 are bona fide and 31 are candidate RR Lyrae stars, 71 are Cepheids, and 16 are binary systems) by applying the image subtraction technique to the selected portions of the observed fields. Differential flux light curves were obtained for the vast majority of these variables. Our sample mainly includes pulsating stars that populate the instability strip from the Classical Cepheids down to the RR Lyrae stars, thus tracing the different stellar generations in these regions of M31 down to the horizontal branch of the oldest (t {approx} 10 Gyr) component.

  18. Period-color and amplitude-color relations for RR Lyrae stars

    Science.gov (United States)

    Kanbur, S.; Bhardwaj, A.; Singh, H. P.; Ngeow, C. C.

    2016-05-01

    We use published OGLE LMC/SMC data to present comprehensive period-color (PC) and amplitude-color (AC) relations for both fundamental and overtone stars. For fundamental mode stars, we confirm earlier work that the minimum light extinction corrected PC relation in V - I has a shallow slope but with considerable scatter (LMC: [0.093+-0.019] with a standard deviation about this line of 0.116, SMC: [0.055+-0.058] with a standard deviation about this line of 0.099). We note the high scatter about this line for both the LMC and SMC: either there is some source of uncertainty in extinction or some other physical parameter is responsible for this dispersion. We compare with previous results and discuss some possible causes for this scatter. In contrast, RRc overtone stars do not obey a flat PC relation at minimum light (LMC: [0.604+-0.041] with a standard deviation about this line of 0.109, SMC: [0.472+-0.265] with a standard deviation about this line of 0.091). The fact that fundamental mode RR Lyrae stars obey a flat relation at minimum light and overtone RR Lyrae stars do not is consistent with the interaction of the stellar photosphere and hydrogen ionization front. We compare these results with PC relations for fundamental mode and first overtone Cepheids. The fact that the PC relations change significantly as a function of phase indicates strongly that Cepheid and RR Lyrae relations can only be understood at mean light when their properties as a function of phase are determined.

  19. Persistent C II absorption in the normal type Ia supernova 2002fk

    International Nuclear Information System (INIS)

    We present well-sampled UBVRIJHK photometry of SN 2002fk starting 12 days before maximum light through 122 days after peak brightness, along with a series of 15 optical spectra from –4 to +95 days since maximum. Our observations show the presence of C II lines in the early-time spectra of SN 2002fk, expanding at 11,000 km s–1 and persisting until 8 days past maximum light with a velocity of ∼9000 km s–1. SN 2002fk is characterized by a small velocity gradient of v-dot Si II=26 km s–1 day–1, possibly caused by an off-center explosion with the ignition region oriented toward the observer. The connection between the viewing angle of an off-center explosion and the presence of C II in the early-time spectrum suggests that the observation of C II could be also due to a viewing angle effect. Adopting the Cepheid distance to NGC 1309 we provide the first H 0 value based on near-infrared (near-IR) measurements of a Type Ia supernova (SN) between 63.0 ± 0.8 (±3.4 systematic) and 66.7 ± 1.0 (±3.5 systematic) km s–1 Mpc–1, depending on the absolute magnitude/decline rate relationship adopted. It appears that the near-IR yields somewhat lower (6%-9%) H 0 values than the optical. It is essential to further examine this issue by (1) expanding the sample of high-quality near-IR light curves of SNe in the Hubble flow, and (2) increasing the number of nearby SNe with near-IR SN light curves and precise Cepheid distances, which affords the promise to deliver a more precise determination of H 0.

  20. Obituary: Theodore Siegumfeldt Jacobsen, 1901-2003

    Science.gov (United States)

    Kraft, Robert Paul; Wallerstein, George

    2003-12-01

    Theodor Jacobsen, oldest member of the American Astronomical Society, died in Seattle on 17 July 2003 at the age of 102. His astronomical career, which began in the 1920's, coincided with the rise of astronomy in the University of Washington from a one-man activity within mathematics to today's major astronomical department of more than 30 faculty and other research personnel. Born on 6 February 1901 in Copenhagen, Denmark, he immigrated with his parents, brother and three sisters to the USA in 1917. Even while he was still in Denmark, his interest in astronomy was sparked at age 7 by a gift from his parents of a two-inch telescope. As early as 1921, in the midst of his undergraduate studies in chemistry at Stanford, he wrote to Director W. W. Campbell of Lick Observatory, inquiring how he should prepare for a career in astronomy and whether one could make a living at it. Campbell encouraged him to learn as much physics and mathematics as possible with the outcome that, on completion of his BA degree at Stanford, Jacobsen became a University of California Berkeley graduate student and was appointed a Lick Observatory fellow in the period 1923 to 1926. Following completion of his PhD thesis, entitled ``A Redetermination of the Radial Velocity Curves of Certain Cepheid Variable Stars" (LOB, 379, 1926), he was appointed as ``assistant" at Lick, a position roughly equivalent to that of ``instructor" in a modern University environment. Inquiries concerning whether Lick could recommend ``a promising young man to take over teaching some astronomy and math" from then President Spencer of the University of Washington were received by Lick's acting director Robert Aitken in 1928. They were looking for a Berkeley PhD, said Spencer, and Aitken responded with an enthusiastic recommendation of Theodor Jacobsen, who then took up his duties in Seattle with the beginning of the fall term 1928. Jacobsen succeeded H. Zanstra (of Zanstra mechanism fame) in the Dept. of Mathematics

  1. Development Status of the WetLab-2 Project: New Tools for On-orbit Real-time Quantitative Gene Expression.

    Science.gov (United States)

    Jung, Jimmy; Parra, Macarena P.; Almeida, Eduardo; Boone, Travis; Chinn, Tori; Ricco, Antonio; Souza, Kenneth; Hyde, Liz; Rukhsana, Yousuf; Richey, C. Scott

    2013-01-01

    The primary objective of NASA Ames Research Centers WetLab-2 Project is to place on the ISS a research platform to facilitate gene expression analysis via quantitative real-time PCR (qRT-PCR) of biological specimens grown or cultured on orbit. The WetLab-2 equipment will be capable of processing multiple sample types ranging from microbial cultures to animal tissues dissected on-orbit. In addition to the logistical benefits of in-situ sample processing and analysis, conducting qRT-PCR on-orbit eliminates the confounding effects on gene expression of reentry stresses and shock acting on live cells and organisms. The system can also validate terrestrial analyses of samples returned from ISS by providing quantitative on-orbit gene expression benchmarking prior to sample return. The ability to get on orbit data will provide investigators with the opportunity to adjust experimental parameters for subsequent trials based on the real-time data analysis without need for sample return and re-flight. Finally, WetLab-2 can be used for analysis of air, surface, water, and clinical samples to monitor environmental contaminants and crew health. The verification flight of the instrument is scheduled to launch on SpaceX-5 in Aug. 2014.Progress to date: The WetLab-2 project completed a thorough study of commercially available qRT-PCR systems and performed a downselect based on both scientific and engineering requirements. The selected instrument, the Cepheid SmartCycler, has advantages including modular design (16 independent PCR modules), low power consumption, and rapid ramp times. The SmartCycler has multiplex capabilities, assaying up to four genes of interest in each of the 16 modules. The WetLab-2 team is currently working with Cepheid to modify the unit for housing within an EXPRESS rack locker on the ISS. This will enable the downlink of data to the ground and provide uplink capabilities for programming, commanding, monitoring, and instrument maintenance. The project is

  2. 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

  3. Homogeneous Photometry VI: Variable Stars in the Leo I Dwarf Spheroidal Galaxy?

    CERN Document Server

    Stetson, Peter B; Bono, Giuseppe; Bernard, Edouard J; Monelli, Matteo; Iannicola, Giacinto; Gallart, Carme; Ferraro, Ivan

    2014-01-01

    We have characterized the pulsation properties of 164 candidate RR Lyrae variables (RRLs) and 55 candidate Anomalous and/or short-period Cepheids in Leo I dwarf spheroidal galaxy. On the basis of its RRLs Leo I is confirmed to be an Oosterhoff-intermediate type galaxy, like several other dwarfs. We show that in their pulsation properties, the RRLs representing the oldest stellar population in the galaxy are not significantly different from those of five other nearby, isolated dwarf spheroidal galaxies. A similar result is obtained when comparing them to RR Lyrae stars in recently discovered ultra-faint dwarf galaxies. We are able to compare the period distributions and period-amplitude relations for a statistically significant sample of ab type RR Lyrae stars in dwarf galaxies (~1300stars) with those in the Galactic halo field (~14,000stars) and globular clusters (~1000stars). Field RRLs show a significant change in their period distribution when moving from the inner (dG14kpc) halo regions. This suggests tha...

  4. Neighboring Galaxies' Influence on Rotation Curve Asymmetry

    CERN Document Server

    Hodge, J C; Castelaz, Michael W.; Hodge, John C.

    2003-01-01

    The rotation velocity asymmetry v observed in spiral galaxy HI rotation curves linearly correlates with the effective potential force from the 10 closest neighboring galaxies normalized for the test particle mass and the gravitational constant. The magnitude of the potential force from a close galaxy is proportional to the luminosity of the close galaxy and inversely proportional to the square of the distance from the close galaxy to the target galaxy. The correlation coefficient is 0.99 and F test is 0.99. Also, the slope of the rotation curve in the disk region of a galaxy from rising to flat to declining is qualitatively correlated with increasing asymmetry and, hence, to the net force from other galaxies. The result is based on a sample of nine spiral galaxies with published Cepheid distances and rotation curves and with a wide range of characteristics. These relationships are interesting not only for their predictive power but also because (1) they suggest a galaxy's dynamics and the shape of its rotatio...

  5. HIV-associated TB syndemic: A growing clinical challenge worldwide

    Directory of Open Access Journals (Sweden)

    Maria Theresa Montales

    2015-12-01

    Full Text Available The association of tuberculosis (TB with human immunodeficiency virus (HIV infection and acquired immune deficiency syndrome (AIDS over the past several years has become an emerging syndemic. Approximately 10% of people living with HIV (PLHIV with latent TB infection will develop active TB disease each year. In this review, we highlight that this phenomenon is not limited to high endemic regions like Afro-Asian nations, but globalization/migration is causing increased case detection even in developed nations such as the United States (US. Active screening should be performed for tuberculosis in PLHIV. A high degree of clinical suspicion for tuberculosis is warranted in PLHIV presenting with fever, cough and unintentional weight loss. HIV-Mycobacterium tuberculosis (MTB coinfection is often paucibacillary, precluding diagnosis by conventional diagnostics and/or smear-microscopy/culture. Improved detection of pulmonary and extrapulmonary tuberculosis is now possible by incorporation of the GeneXPERT MTB/RIF assay (Cepheid Inc, Sunnyvale, USA. The World Health Organization (WHO recommends instituting immediate therapy for Mycobacterium tuberculosis, in conjunction with ongoing or newly introduced antiretroviral therapy (ART. Vigilance is required to detect drug-induced organ injuries, and early-treatment induced immune reconstitution inflammatory syndrome (IRIS. Collaborating MTB and HIV activities in concentrated HIV epidemic settings should become a high public health priority.

  6. The Araucaria Project: The distance to the Carina Dwarf Galaxy from infrared photometry of RR Lyrae stars

    CERN Document Server

    Karczmarek, P; Gieren, W; Suchomska, K; Konorski, P; Górski, M; Pilecki, B; Graczyk, D; Wielgórski, P

    2015-01-01

    We obtained single-phase near-infrared (NIR) magnitudes in the $J$- and $K$-band for a sample of 33 RR Lyrae stars in the Carina dSph galaxy. Applying different theoretical and empirical calibrations of the NIR period-luminosity-metallicity relation for RR Lyrae stars, we find consistent results and obtain a true, reddening-corrected distance modulus of 20.118 $\\pm$ 0.017 (statistical) $\\pm$ 0.11 (systematic) mag. This value is in excellent agreement with the results obtained in the context of the Araucaria Project from NIR photometry of Red Clump stars (20.165 $\\pm$ 0.015) and Tip of Red Giant Branch (20.09 $\\pm$ 0.03 $\\pm$ 0.12 mag in $J$-band, 20.14 $\\pm$ 0.04 $\\pm$ 0.14 mag in $K$-band), as well as with most independent distance determinations to this galaxy. The near-infrared RR Lyrae method proved to be a reliable tool for accurate distance determination at the 5 percent level or better, particularly for galaxies and globular clusters that lack young standard candles, like Cepheids.

  7. 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...

  8. 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...

  9. Hubble trouble or Hubble bubble?

    CERN Document Server

    Romano, Antonio Enea

    2016-01-01

    The recent analysis of low-redshift supernovae (SN) has increased the apparent tension between the value of $H_0$ estimated from low and high red-shift observations such as the cosmic microwave background (CMB) radiation. On the other hand other observations have provided strong evidence for the existence of a local underdensity extending up to a red-shift of about $0.07$. We compute with different methods the effects of this local void on the low-redshift luminosity distance using an exact solution of the Einstein's equations, linear perturbation theory and a low-redshift expansion. The correction is proportional to the volume averaged density contrast and to the comoving distance form the center and is able to completely resolve the apparent $H_0$ tension. The void does not affect the high red-shift luminosity distance because the volume averaged density contrast tends to zero asymptotically. Since all the Cepheids used for the luminosity distance calibration are inside this local void, not properly taking ...

  10. Autoclassification of the Variable 3XMM Sources Using the Random Forest Machine Learning Algorithm

    Science.gov (United States)

    Farrell, Sean A.; Murphy, Tara; Lo, Kitty K.

    2015-11-01

    In the current era of large surveys and massive data sets, autoclassification of astrophysical sources using intelligent algorithms is becoming increasingly important. In this paper we present the catalog of variable sources in the Third XMM-Newton Serendipitous Source catalog (3XMM) autoclassified using the Random Forest machine learning algorithm. We used a sample of manually classified variable sources from the second data release of the XMM-Newton catalogs (2XMMi-DR2) to train the classifier, obtaining an accuracy of ∼92%. We also evaluated the effectiveness of identifying spurious detections using a sample of spurious sources, achieving an accuracy of ∼95%. Manual investigation of a random sample of classified sources confirmed these accuracy levels and showed that the Random Forest machine learning algorithm is highly effective at automatically classifying 3XMM sources. Here we present the catalog of classified 3XMM variable sources. We also present three previously unidentified unusual sources that were flagged as outlier sources by the algorithm: a new candidate supergiant fast X-ray transient, a 400 s X-ray pulsar, and an eclipsing 5 hr binary system coincident with a known Cepheid.

  11. A Portrait of One Hundred Thousand and One Galaxies

    Science.gov (United States)

    2002-08-01

    Rich and Inspiring Experience with NGC 300 Images from the ESO Science Data Archive Summary A series of wide-field images centred on the nearby spiral galaxy NGC 300 , obtained with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory , have been combined into a magnificent colour photo. These images have been used by different groups of astronomers for various kinds of scientific investigations, ranging from individual stars and nebulae in NGC 300, to distant galaxies and other objects in the background. This material provides an interesting demonstration of the multiple use of astronomical data, now facilitated by the establishment of extensively documented data archives, like the ESO Science Data Archive that now is growing rapidly and already contains over 15 Terabyte. Based on the concept of Astronomical Virtual Observatories (AVOs) , the use of archival data sets is on the rise and provides a large number of scientists with excellent opportunities for front-line investigations without having to wait for precious observing time. In addition to presenting a magnificent astronomical photo, the present account also illustrates this important new tool of the modern science of astronomy and astrophysics. PR Photo 18a/02 : WFI colour image of spiral galaxy NGC 300 (full field) . PR Photo 18b/02 : Cepheid stars in NGC 300 PR Photo 18c/02 : H-alpha image of NGC 300 PR Photo 18d/02 : Distant cluster of galaxies CL0053-37 in the NGC 300 field PR Photo 18e/02 : Dark matter distribution in CL0053-37 PR Photo 18f/02 : Distant, reddened cluster of galaxies in the NGC 300 field PR Photo 18g/02 : Distant galaxies, seen through the outskirts of NGC 300 PR Photo 18h/02 : "The View Beyond" ESO PR Photo 18a/02 ESO PR Photo 18a/02 [Preview - JPEG: 400 x 412 pix - 112k] [Normal - JPEG: 1200 x 1237 pix - 1.7M] [Hi-Res - JPEG: 4000 x 4123 pix - 20.3M] Caption : PR Photo 18a/02 is a reproduction of a colour-composite image of the nearby spiral galaxy

  12. Pulsation period variations in the RRc Lyrae star KIC 5520878

    CERN Document Server

    Hippke, Michael; Zee, A; Edmondson, William H; Steven, Ian R; Lindner, John F; Kia, Benham; Ditto, William L

    2014-01-01

    Learned et. al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among variable stars using photometric data from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have found two such regimes of long and short pulse durations. The sequence of period lengths, expressed as time series data, is strongly auto correlated, with correlation coefficients of prime numbers being significantly higher ($p=99.8$\\%). Our analysis of this candidate star shows that the prime number oddity o...

  13. The Gaia-ESO Survey: Probes of the inner disk abundance gradient

    CERN Document Server

    Jacobson, H R; Jilkova, L; Magrini, L; Bragaglia, A; Vallenari, A; Tosi, M; Randich, S; Donati, P; Cantat-Gaudin, T; Sordo, R; Smiljanic, R; Overbeek, J C; Carraro, G; Tautvaisiene, G; Roman, I San; Villanova, S; Geisler, D; Munoz, C; Jimenez-Esteban, F; Tang, B; Gilmore, G; Alfaro, E J; Bensby, T; Flaccomio, E; Koposov, S E; Korn, A J; Pancino, E; Recio-Blanco, A; Casey, A R; Costado, M T; Franciosini, E; Heiter, U; Hill, V; Hourihane, A; Lardo, C; de Laverny, P; Lewis, J; Monaco, L; Morbidelli, L; Sacco, G G; Sousa, S G; Worley, C C; Zaggia, S

    2016-01-01

    The nature of the metallicity gradient inside the solar circle (R_GC < 8 kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. We investigate the metallicity gradient of the inner disk using a sample of inner disk open clusters that is three times larger than has previously been studied in the literature to better characterize the gradient in this part of the disk. We used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H] values were determined based on a membership analysis for each cluster. Where necessary, distances and ages to clusters were determined via comparison to theoretical isochrones. The GES open clusters exhibit a radial metallicity gradient of -0.10+-0.02 dex/kpc, consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range R_GC ~ 6-12 kpc. We also measure ...

  14. PULSATION PERIOD VARIATIONS IN THE RRc LYRAE STAR KIC 5520878

    Energy Technology Data Exchange (ETDEWEB)

    Hippke, Michael [Institute for Data Analysis, Luiter Str. 21b, D-47506 Neukirchen-Vluyn (Germany); Learned, John G. [High Energy Physics Group, Department of Physics and Astronomy, University of Hawaii, Manoa 327 Watanabe Hall, 2505 Correa Road, Honolulu, HI 96822 (United States); Zee, A. [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Edmondson, William H. [School of Computer Science, University of Birmingham, Birmingham B15 2TT (United Kingdom); Lindner, John F. [Physics Department, The College of Wooster, Wooster, OH 44691 (United States); Kia, Behnam; Ditto, William L. [Department of Physics and Astronomy, University of Hawai' i at Mānoa, Honolulu, HI 96822 (United States); Stevens, Ian R., E-mail: hippke@ifda.eu, E-mail: jgl@phys.hawaii.edu, E-mail: zee@kitp.ucsb.edu, E-mail: w.h.edmondson@bham.ac.uk, E-mail: jlindner@wooster.edu, E-mail: wditto@hawaii.edu, E-mail: behnam@hawaii.edu, E-mail: irs@star.sr.bham.ac.uk [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom)

    2015-01-01

    Learned et al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among variable stars using photometric data from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have found two such regimes of long and short pulse durations. The sequence of period lengths, expressed as time series data, is strongly autocorrelated, with correlation coefficients of prime numbers being significantly higher (p = 99.8%). Our analysis of this candidate star shows that the prime number oddity originates from two simultaneous pulsation periods and is likely of natural origin. Simple physical models elucidate the frequency content and asymmetries of the KIC 5520878 light curve. Despite this SETI null result, we encourage testing of other archival and future time-series photometry for signs of modulated stars. This can be done as a by-product to the standard analysis, and can even be partly automated.

  15. The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system

    CERN Document Server

    Fauvaud, S; Ribas, I; Rodríguez, E; Lampens, P; Klingenberg, G; Farrell, J A; Fumagalli, F; Simonetti, J H; Wolf, M; Santacana, G; Zhou, A -Y; Michel, R; Fox-Machado, L; Alvarez, M; Nava-Vega, A; López-González, M J; Casanova, V M; Aceituno, F J; Scheggia, I; Rives, J -J; Hintz, E G; Van Cauteren, P; Helvaci, M; Yesilyaprak, C; Graham, K A; Král, L; Kocián, R; Kučáková, H; Fauvaud, M; Granslo, B H; Michelet, J; Nicholson, M P; Vugnon, J -M; Kotková, L; Truparová, K; Ulusoy, C; Yasarsoy, B; Avdibegovic, A; Blauzek, M; Kliner, J; Zasche, P; Bartošíková, S; Vilášek, M; Trondal, O; Abbeel, F Van Den; Behrend, R; Wücher, H

    2010-01-01

    Short-period high-amplitude pulsating stars of Population I ($\\delta$ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. aims heading (mandatory) We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses. methods heading (mandatory) An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. results heading (mandatory) In addition to a po...

  16. 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.

  17. Variability of Massive Stars with Known Spectral Types in the Small Magellanic Cloud Using 8 Years of OGLE-III Data

    CERN Document Server

    Kourniotis, M; Soszynski, I; Poleski, R; Krikelis, G; Udalski, A; Szymanski, M K; Kubiak, M; Pietrzynski, G; Wyrzykowski, L; Ulaczyk, K; Kozlowski, S; Pietrukowicz, P

    2013-01-01

    We present a variability study of 4646 massive stars in the Small Magellanic Cloud (SMC) with known spectral types from the catalog of Bonanos et al. (2010) using the light curves from OGLE-III database. The goal is to exploit the time domain information available through OGLE-III to gain insight into the processes that govern the evolution of massive stars. We find 60% of our sample (2766 stars) to be "constant" and 40% (1880 stars) to exhibit variability distributed as follows: 807 stars display low-amplitude stochastic variability with fluctuations in I-band of 0.05 mag, 443 stars present irregular variability of higher amplitude (76% of these are reported as variables for the first time), 212 are eclipsing binaries, including 108 newly discovered systems, 43 are candidate rotating variables, 126 are classical Cepheids, 188 stars exhibit short-term sinusoidal periodicity (P < 3 days) making them candidate "slowly pulsating B stars" and non-radial Be pulsators, and 61 periodic stars exhibit longer period...

  18. Confirmation of a Star Formation Bias in Type Ia Supernova Distances and its Effect on Measurement of the Hubble Constant

    CERN Document Server

    Rigault, M; Kowalski, M; Copin, Y; Antilogus, P; Aragon, C; Bailey, S; Baltay, C; Baugh, D; Bongard, S; Boone, K; Buton, C; Chen, J; Chotard, N; Fakhouri, H K; Feindt, U; Fagrelius, P; Fleury, M; Fouchez, D; Gangler, E; Hayden, B; Kim, A G; Leget, P -F; Lombardo, S; Nordin, J; Pain, R; Pecontal, E; Pereira, R; Perlmutter, S; Rabinowitz, D; Runge, K; Rubin, D; Saunders, C; Smadja, G; Sofiatti, C; Suzuki, N; Tao, C; Weaver, B A

    2014-01-01

    Previously we used the Nearby Supernova Factory sample to show that SNe~Ia having locally star-forming environments are dimmer than SNe~Ia having locally passive environments.Here we use the \\constitution\\ sample together with host galaxy data from \\GALEX\\ to independently confirm that result. The effect is seen using both the SALT2 and MLCS2k2 lightcurve fitting and standardization methods, with brightness differences of $0.094 \\pm 0.037\\ \\mathrm{mag}$ for SALT2 and $0.155 \\pm 0.041\\ \\mathrm{mag}$ for MLCS2k2 with $R_V=2.5$. When combined with our previous measurement the effect is $0.094 \\pm 0.025\\ \\mathrm{mag}$ for SALT2. If the ratio of these local SN~Ia environments changes with redshift or sample selection, this can lead to a bias in cosmological measurements. We explore this issue further, using as an example the direct measurement of $H_0$. \\GALEX{} observations show that the SNe~Ia having standardized absolute magnitudes calibrated via the Cepheid period--luminosity relation using {\\textit{HST}} orig...

  19. The distance to NGC1316 (Fornax A): yet another curious case

    CERN Document Server

    Cantiello, Michele; Blakeslee, John P; Di Rico, Gianluca; Limatola, Luca; Brocato, Enzo; Della Valle, Massimo; Gilmozzi, Roberto

    2013-01-01

    The distance of NGC1316, the brightest galaxy in Fornax, is an interesting test for the cosmological distance scale. First, because Fornax is the 2nd largest cluster of galaxies at <~25 Mpc after Virgo and, in contrast to Virgo, has a small line-of-sight depth; and second, because NGC1316 is the galaxy with the largest number of detected SNeIa, giving the opportunity to test the consistency of SNeIa distances internally and against other indicators. We measure SBF mags in NGC1316 from ground and space-based imaging data, providing a homogeneous set of measurements over a wide wavelength interval. The SBF, coupled with empirical and theoretical calibrations, are used to estimate the distance to the galaxy. We present the first B-band SBF measurements of NGC1316 and use them together with the optical and near-IR SBF data to analyze the properties of field stars. Our distance modulus m-M=31.59 +-0.05(stat) +-0.14(sys), when placed in a consistent Cepheid distance scale, agrees with the results from other indi...

  20. Revealing {\\delta} Cephei's Secret Companion and Intriguing Past

    CERN Document Server

    Anderson, Richard I; Holl, Berry; Eyer, Laurent; Palaversa, Lovro; Mowlavi, Nami; Süveges, Maria; Roelens, Maroussia

    2015-01-01

    Classical Cepheid variable stars are crucial calibrators of the cosmic distance scale thanks to a relation between their pulsation periods and luminosities. Their archetype, {\\delta} Cephei, is an important calibrator for this relation. In this paper, we show that {\\delta} Cephei is a spectroscopic binary based on newly-obtained high-precision radial velocities. We combine these new data with literature data to determine the orbit, which has period 2201 days, semi-amplitude 1.5 km/s, and high eccentricity (e = 0.647). We re-analyze Hipparcos intermediate astrometric data to measure {\\delta} Cephei's parallax ($\\varpi = 4.09 \\pm 0.16$ mas) and find tentative evidence for an orbital signature, although we cannot claim detection. We estimate that Gaia will fully determine the astrometric orbit. Using the available information from spectroscopy, velocimetry, astrometry, and Geneva stellar evolution models ($M_{\\delta Cep} ~ 5.0 - 5.25 M_\\odot$), we constrain the companion mass to within $0.2 < M_2 < 1.2 M_\\...

  1. Photospheric magnitude diagrams for type II supernovat: A promising tool to compute distances

    International Nuclear Information System (INIS)

    We develop an empirical color-based standardization for Type II supernovae (SNe II), equivalent to the classical surface brightness method given in Wesselink. We calibrate this standardization using SNe II with host galaxy distances measured using Cepheids, and a well-constrained shock breakout epoch and extinction due to the host galaxy. We estimate the reddening with an analysis of the B – V versus V – I color-color curves, similar to that of Natali et al. With four SNe II meeting the above requirements, we build a photospheric magnitude versus color diagram (similar to an H-R diagram) with a dispersion of 0.29 mag. We also show that when using time since shock breakout instead of color as the independent variable, the same standardization gives a dispersion of 0.09 mag. Moreover, we show that the above time-based standardization corresponds to the generalization of the standardized candle method of Hamuy and Pinto for various epochs throughout the photospheric phase. To test the new tool, we construct Hubble diagrams for different subsamples of 50 low-redshift (cz < 104 km s–1) SNe II. For 13 SNe within the Hubble flow (cz CMB > 3000 km s–1) and with a well-constrained shock breakout epoch we obtain values of 68-69 km s–1 Mpc–1 for the Hubble constant and a mean intrinsic scatter of 0.12 mag or 6% in relative distances.

  2. Variable stars towards the bulge of M 31: The AGAPE catalogue

    Science.gov (United States)

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

    2004-07-01

    We present the AGAPE astrometric and photometric catalogue of 1579 variable stars in a 14' × 10' field centred on M 31. This work is the first survey devoted to variable stars in the bulge of M 31. The R magnitudes of the objects and the B-R colours suggest that our sample is dominated by red long-period variable stars (LPV), with a possible overlap with Cepheid-like type II stars. Fits of the light curves with sinusoids suggest that a large fraction of the stars correspond to periodic or semi-periodic objects with periods longer than 100 days. Twelve nova candidates are identified. Correlations with other catalogues suggest that 2 novae could be recurrent novae and provide possible optical counterparts for 2 supersoft X-ray sources candidates observed with Chandra. The full Table \\ref{table3} is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/421/509 Based on data collected with the 2 m Bernard Lyot Telescope (TBL) operated by INSU-CNRS and Observatoire Midi-Pyrénées (USR 5026). The experiment was funded by IN2P3 and INSU of CNRS.

  3. Comparison of Xpert Flu rapid nucleic acid testing with rapid antigen testing for the diagnosis of influenza A and B.

    Science.gov (United States)

    DiMaio, Michael A; Sahoo, Malaya K; Waggoner, Jesse; Pinsky, Benjamin A

    2012-12-01

    Influenza infections are associated with thousands of hospital admissions and deaths each year. Rapid detection of influenza is important for prompt initiation of antiviral therapy and appropriate patient triage. In this study the Cepheid Xpert Flu assay was compared with two rapid antigen tests, BinaxNOW Influenza A & B and BD Directigen EZ Flu A+B, as well as direct fluorescent antibody testing for the rapid detection of influenza A and B. Using real-time, hydrolysis probe-based, reverse transcriptase PCR as the reference method, influenza A sensitivity was 97.3% for Xpert Flu, 95.9% for direct fluorescent antibody testing, 62.2% for BinaxNOW, and 71.6% for BD Directigen. Influenza B sensitivity was 100% for Xpert Flu and direct fluorescent antibody testing, 54.5% for BinaxNOW, and 48.5% for BD Directigen. Specificity for influenza A was 100% for Xpert Flu, BinaxNOW, and BD Directigen, and 99.2% for direct fluorescent antibody testing. All methods demonstrated 100% specificity for influenza B. These findings support the use of the Xpert Flu assay in settings requiring urgent diagnosis of influenza A and B. PMID:22841669

  4. The role of rapid diagnostic tests in managing adults with pneumonia in low-resource settings

    Directory of Open Access Journals (Sweden)

    Stephen J Aston

    2014-06-01

    Full Text Available In well-resourced settings the systematic use of rapid diagnostics tests (e.g. pneumococcal urinary antigen test that define the causal pathogen to direct therapy has not resulted in significantly improved outcomes in adults with pneumonia. The management of pneumonia in many low-resource settings is complicated by a substantial burden of tuberculosis and HIV-associated opportunistic infections, in addition to the usual spectrum of pathogens seen in well-resourced settings. Clinical features alone do not reliably distinguish between these different aetiologies and physicians often have to treat empirically. Given the limitations in diagnostic laboratory capability present in most low-resource settings, rapid and point-of-care diagnostic tests could become valuable tools to guide treatment decisions. Pneumococcal and Legionella urinary antigen tests are specific and moderately sensitive, but their utility in low-resource settings is uncertain. The Xpert MTB/RIF (Cepheid, USA platform and rapid assays for urinary lipoarabinomannan can substantially speed up tuberculosis diagnosis; the current challenge is to translate this into earlier treatment and hopefully improve patient outcome. In HIV-infected patients, 1-3-β-D-glucan is a serum marker of Pneumocystis jirovecii infection with excellent sensitivity. Further studies are needed to assess the clinical utility and cost-effectiveness of these rapid diagnostic assays when they are incorporated into treatment algorithms.

  5. Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

    Science.gov (United States)

    Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Cacciari, C.; Clementini, C.

    2016-05-01

    We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a least squares deconvolution (LSD) of the line profiles in order to an- alyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (+- 2 kms^-1) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 kms^-1 even with a low number of high- resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

  6. Spitzer Spectroscopy of Mass Loss and Dust Production by Evolved Stars in Globular Clusters

    CERN Document Server

    Sloan, G C; Matsuura, M; Zijlstra, A A; Kraemer, K E; Wood, P R; Nieusma, J; Bernard-Salas, J; Devost, D; Houck, J R

    2010-01-01

    We have observed a sample of 35 long-period variables and four Cepheid variables in the vicinity of 23 Galactic globular clusters using the Infrared Spectrograph on the Spitzer Space Telescope. The long-period variables in the sample cover a range of metallicities from near solar to about 1/40th solar. The dust mass-loss rate from the stars increases with pulsation period and bolometric luminosity. Higher mass-loss rates are associated with greater contributions from silicate grains. The dust mass-loss rate also depends on metallicity. The dependence is most clear when segregating the sample by dust composition, less clear when segregating by bolometric magnitude, and absent when segregating by period. The spectra are rich in solid-state and molecular features. Emission from alumina dust is apparent across the range of metallicities. Spectra with a 13-um dust emission feature, as well as an associated feature at 20 um, also appear at most metallicities. Molecular features in the spectra include H_2O bands at ...

  7. RR Lyrae Distance Scale: Theory and Observations

    CERN Document Server

    Bono, G

    2003-01-01

    The RR Lyrae distance scale is reviewed. In particular, we discuss theoretical and empirical methods currently adopted in the literature. Moreover, we also outline pros and cons of optical and near-infrared mean magnitudes to overcome some of the problems currently affecting RR Lyrae distances. The importance of the K-band Period-Luminosity-Metallicity (PLZ_K) relation for RR Lyrae is also discussed, together with the absolute calibration of the zero-point. We also mention some preliminary results based on NIR (J,K) time series data of the LMC cluster Reticulum. This cluster hosts a sizable sample of RR Lyrae and its distance is found to be 18.45 +/- 0.04 mag using the predicted PLZ_K relation and 18.51 +/- 0.06 using the PLZ_J relation. We briefly discuss the evolutionary status of Anomalous Cepheids and their possible use as distance indicators. Finally, we point out some possible improvements to improve the intrinsic accuracy of theory and observations.

  8. Cool neutral hydrogen in the direction of an anonymous OB association

    International Nuclear Information System (INIS)

    H I self-absorption is seen in the direction l = 55.06 probably physically associated with an anonymous OB association which has the Cepheid GY Sagittae as a member. The cool H I is in two clouds at least 15 pc in diameter located 3.25 kpc from the Sun. If their temperature is approx. =50 K, the cloud masses are approx. =103 M/sub sun/. The neutral atomic hydrogen clouds are probably warm envelopes surrounding cold molecular cloud cores because CO observations in this region show two molecular clouds nearly coincident with the absorbing H i gas. Since the OB association is only approx. =107 years old, these clouds are likely to be part of the original cloud complex from which the stellar cluster formed. The H i clouds are part of the larger Arecibo survey of self-absorption which suggests that many of the Arecibo clouds are associated with heretofore unidentified star clusters. Even if this is generally not the case, the Arecibo objects have accurate kinematic distances and thus provide a new sample of cool H I clouds whose thermodynamic properties can be studied

  9. GAIA accuracy on radial velocities assessed from a synthetic spectra database

    CERN Document Server

    Zwitter, T

    2002-01-01

    Spectrograph aboard the GAIA satellite operates in the near-IR, in the 8490-- 8740 \\AA window accessible also from the ground. The most important parameter yet to be determined is the spectral resolution. Realistic estimates of the zodiacal light background are obtained and a total of $2\\times 10^5$ correlation runs are used to study the accuracy of radial velocity measured by the spectrograph as a function of resolution, magnitude of the target, its spectral type and luminosity class. Accuracy better than 2 km/s is achievable for bright stars if a high enough dispersion is chosen. Radial velocity error of 5 km/s is at $V=17.5$ for Cepheids and at 17.7 for horizontal branch stars. Even for very faint objects, with spectra dominated by background and readout noise, the optimal dispersion is still in the 0.25 / 0.75 \\AA/pix range. This is also true for complicated cases such as spectroscopic binaries or if information other than radial velocity, i.e. abundances of individual elements or stellar rotation velocit...

  10. Distances to nearby galaxies combining fragmentary data using four different methods

    CERN Document Server

    Huterer, D; Schechter, P L; Huterer, Dragan; Sasselov, Dimitar D; Schechter, Paul L

    1995-01-01

    The primary distance indicators are established in our Galaxy and the Local Group. There are at least four different methods which give good distances: methods using proper motions, RR Lyraes, Cepheid variables, and Type II supernovae. However the data on independent distances is very fragmentary, due partly to nature and partly to technological limits. As a result the data are rarely put together in a consistent way; instead, the discussion of distance scales is often focused on one or two methods or on individual objects. Hence the question: what is the current situation with our overall knowledge of distances to the nearby galaxies? We try to answer this question by combining the fragmentary data from all four methods for fifteen objects: the galactic center, the globular clusters M2, M3, M4, M13, M22, M92, and 47 Tuc, the galaxies IC1613, M31, M33, M81, M100 and M101, and the Large Magellanic Cloud. We pay special attention to covariances among the different distance estimates. This most complete combinat...

  11. Deep Wide Field BVI CCD Photometry of the Sextans Dwarf Spheroidal Galaxy

    CERN Document Server

    Lee, M G; Park, J H; Sohn, Y J; Oh, S J; Yuk, I S; Rey, S C; Lee, S G; Lee, Y W; Kim, H I; Han, W; Park, W K; Lee, J H; Jeon, Y B; Kim, S C; Lee, Myung Goon; Park, Hong Soo; Park, Jang-Hyun; Sohn, Young-Jong; Oh, Seung Joon; Yuk, In-Soo; Rey, Soo-Chang; Lee, Sang-Gak; Lee, Young-Wook; Kim, Ho-Il; Han, Wonyong; Park, Won-Kee; Lee, Joon Hyeop; Jeon, Young Beom; Kim, Sang Chul

    2003-01-01

    We present deep wide field $VI$ CCD photometry of the Sextans dwarf spheroidal galaxy (dSph) in the Local Group, covering a field of 42' x 28' located at the center of the galaxy. Color-magnitude diagrams of the Sextans dSph show well-defined red giant branch (RGB), blue horizontal branch (BHB), prominent red horizontal branch (RHB), asymptotic giant branch (AGB), about 120 variable star candidates including RR Lyraes and anomalous Cepheids, about 230 blue stragglers (BSs), and main sequence (MS) stars. The distance to the galaxy is derived using the $I$-band magnitude of the tip of the RGB at I(TRGB)=15.95+/-0.04: (m-M)_0=19.90+/-0.06 for an adopted reddening of E(B-V)=0.01. The mean metallicity of the RGB is estimated from the (V-I) color: [Fe/H]=-2.1+/-0.1(statistical error) +/-0.2(standard calibration error) dex, with a dispersion of sigma[Fe/H]=0.2 dex. The age of the MSTO of the main old population is estimated to be similar to that of M92, and there are seen some stellar populations with younger age. T...

  12. Development, roll-out and impact of Xpert MTB/RIF for tuberculosis: what lessons have we learnt and how can we do better?

    Science.gov (United States)

    Albert, Heidi; Nathavitharana, Ruvandhi R; Isaacs, Chris; Pai, Madhukar; Denkinger, Claudia M; Boehme, Catharina C

    2016-08-01

    The global roll-out of Xpert MTB/RIF (Cepheid Inc., Sunnyvale, CA, USA) has changed the diagnostic landscape of tuberculosis (TB). More than 16 million tests have been performed in 122 countries since 2011, and detection of multidrug-resistant TB has increased three- to eight-fold compared to conventional testing. The roll-out has galvanised stakeholders, from donors to civil society, and paved the way for universal drug susceptibility testing. It has attracted new product developers to TB, resulting in a robust molecular diagnostics pipeline. However, the roll-out has also highlighted gaps that have constrained scale-up and limited impact on patient outcomes. The roll-out has been hampered by high costs for under-funded programmes, unavailability of a complete solution package (notably comprehensive training, quality assurance, implementation plans, inadequate service and maintenance support) and lack of impact assessment. Insufficient focus has been afforded to effective linkage to care of diagnosed patients, and clinical impact has been blunted by weak health systems. In many countries the private sector plays a dominant role in TB control, yet this sector has limited access to subsidised pricing. In light of these lessons, we advocate for a comprehensive diagnostics implementation approach, including increased engagement of in-country stakeholders for product launch and roll-out, broader systems strengthening in preparation for new technologies, as well as quality impact data from programmatic settings. PMID:27418550

  13. 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...

  14. Polaris: Evolutionary (and Other !) Period Changes and Clues to its Nature

    Science.gov (United States)

    Turner, David G.

    2012-05-01

    O-C data for the Cepheid Polaris derived from its brightness and radial velocity variations are consistent with a regular period increase of 4.5 seconds per year during the past two centuries, with the exception of a unique hiatus circa 1965 when the pulsation period underwent a brief decrease that is difficult to explain without invoking assimilation of a substellar companion. The 30-year cycle of the Polaris Aa subsystem is evident both in the star’s systemic radial velocity variations and observed times of light maximum, the latter of which display light travel time effects larger than expected. Arguments for overtone versus fundamental mode pulsation in the star appear to favor Polaris as an overtone pulsator, which is supported by its potential cluster membership, yet are currently unable to explain all of its observational characteristics: small amplitude in conjunction with location near the center of the instability strip, rapid period increase, X-ray emission, etc. Perhaps future or ongoing space observations will shed light on the puzzle.

  15. Is there a concordance value for $H_0$?

    CERN Document Server

    Luković, Vladimir V; Vittorio, Nicola

    2016-01-01

    We test the theoretical predictions from a number of cosmological models against different observables, to compare the indirect estimates of the present expansion rate, coming from model fitting, with the direct measurements based on Cepheids data from Riess et al. (2016). We perform a statistical analysis of SN Ia, Hubble parameter and BAO data. A joint analysis of these datasets allows to better constrain cosmological parameters, but also to break the degeneracy that appears in the distance modulus definition between $H_0$ and the absolute B-band magnitude of SN Ia, $M_0$. From the theoretical side, we consider flat and non-flat $\\Lambda$CDM, $w$CDM, and inhomogeneous LTB models. For the analysis of SN Ia we follow the approach suggested by Tr{\\o}st Nielsen et al. (2015) to take into account the distributions of SN Ia intrinsic parameters. For the $\\Lambda$CDM model we find that $\\Omega_m=0.35\\pm0.02$, $H_0=(67.8\\pm1.0)\\,$km$\\,$s$^{-1}/$Mpc, while the corrected SN absolute magnitude has a Normal distributio...

  16. Stellar Astrophysics with SIM and Optical Long Baseline Interferometry

    Science.gov (United States)

    Ridgway, Stephen T.; Aufdenberg, J. P.; Boyajian, T.; Gies, D.; Howell, S. B.; Kervella, P.; Merand, A.; Richardson, N.

    2009-01-01

    SIM astrometry can be used in combination with precision ground-based measurements, particularly optical interferometry, and supporting modeling, to address fundamental questions in stellar physics. We will extend an on-going study of Cepheid stars, with emphasis on resolution of possible biases in the use of the P-L relation, aiming for a confidence level of better than 1%. We will determine the radii, Teff, luminosity, and in some cases masses, of massive stars with sufficient accuracy to validate models of their structure and evolution with dramatically improved discrimination. We will determine the orbits of post-Algol systems, to test the hypothesis that they are the precursors to Cataclysmic Variable stars and the wide variety of evolved objects that they produce. We will measure the radii of nearby stars to support asteroseismological studies of the stellar interiors. For all measurements here proposed for SIM, GAIA will not provide a realistic alternative, owing to brightness of the targets, expected errors, and/or required observational cadence.

  17. Improving the distances of post-AGB objects in the Milky Way

    Science.gov (United States)

    Vickers, Shane B.; Frew, David J.; Owers, Matt S.; Parker, Quentin A.; Bojičič, Ivan S.

    2016-07-01

    Post-AGB (PAGB) stars are short-lived, low-intermediate mass objects transitioning from the asymptotic giant branch (AGB) to the white dwarf (WD) phase. These objects are characterised by a constant, core-mass dependent luminosity and a large infrared excess from the dusty envelope ejected at the top of the AGB. PAGB stars provide insights into the evolution of their direct descendants, planetary nebulae (PNe). Calculation of physical characteristics of PAGB are dependent on accurately determined distances scarcely available in the literature. Using the Torun catalogue for PAGB objects, supplemented with archival data, we have determined distances to the known population of Galactic PAGB stars. This is by modelling their spectral energy distributions (SED) with black bodies and numerically integrating over the entire wavelength range to determine the total integrated object flux. For most PAGB stars we assumed their luminosities are based on their positional characteristics and stellar evolution models. RV Tauri stars however are known to follow a period-luminosity relation (PLR) reminiscent of type-2 Cepheids. For these variable PAGB stars we determined their luminosities via the PLR and hence their distances. This allows us to overcome the biggest obstacle to characterising these poorly understood objects that play a vital part in Galactic chemical enrichment.

  18. Hide and seek between Andromeda's halo, disk, and giant stream

    CERN Document Server

    Clementini, Gisella; Federici, Luciana; Macario, Giulia; Beccari, Giacomo; Testa, Vincenzo; Cignoni, Michele; Marconi, Marcella; Ripepi, Vincenzo; Tosi, Monica; Bellazzini, Michele; Pecci, Flavio Fusi; Diolaiti, Emiliano; Cacciari, Carla; Marano, Bruno; Giallongo, Emanuele; Ragazzoni, Roberto; Di Paola, Andrea; Gallozzi, Stefano; Smareglia, Riccardo

    2011-01-01

    Photometry in B, V (down to V ~ 26 mag) is presented for two 23' x 23' fields of the Andromeda galaxy (M31) that were observed with the blue channel camera of the Large Binocular Telescope during the Science Demonstration Time. Each field covers an area of about 5.1kpc x 5.1kpc at the distance of M31 ((m-M)o ~ 24.4 mag), sampling, respectively, a northeast region close to the M31 giant stream (field S2), and an eastern portion of the halo in the direction of the galaxy minor axis (field H1). The stream field spans a region that includes Andromeda's disk and the giant stream, and this is reflected in the complexity of the color magnitude diagram of the field. One corner of the halo field also includes a portion of the giant stream. Even though these demonstration time data were obtained under non-optimal observing conditions the B photometry, acquired in time-series mode, allowed us to identify 274 variable stars (among which 96 are bona fide and 31 are candidate RR Lyrae stars, 71 are Cepheids, and 16 are bin...

  19. 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...

  20. Clustering of Local Group distances: publication bias or correlated measurements? I. The Large Magellanic Cloud

    CERN Document Server

    de Grijs, Richard; Bono, Giuseppe

    2014-01-01

    The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder. Yet, the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly - and with a small spread - around the "canonical" distance modulus, (m-M)_0 = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading ...

  1. Eclipsing binary stars in the Large Magellanic Cloud. Results from the EROS-2, OGLE and VMC surveys

    CERN Document Server

    Muraveva, T; Maceroni, C; Evans, C J; Moretti, M I; Cioni, M -R L; Marquette, J B; Ripepi, V; de Grijs, R; Groenewegen, M A T; Piatti, A E; van Loon, J Th

    2014-01-01

    We present a catalogue of 1768 eclipsing binary stars (EBs) detected in the Large Magellanic Cloud (LMC) by the second generation of the EROS survey (hereinafter EROS-2); 493 of them are new discoveries located in outer regions (out of the central bar) of the LMC. These sources were originally included in a list of candidate classical Cepheids (CCs) extracted from the EROS-2 catalogue on the basis of the period (0.89 $

  2. Radial pulsation as a function of hydrogen abundance

    Science.gov (United States)

    Jeffery, C. S.; Saio, H.

    2016-05-01

    Using linear non-adiabatic pulsation analysis, we explore the radial-mode (p-mode) stability of stars across a wide range of mass (0.2 ≤ M ≤ 50{ M_{{⊙}}}), composition (0 ≤ X ≤ 0.7, Z = 0.001, 0.02), effective temperature (3000 ≤ Teff ≤ 40 000 K), and luminosity (0.01 ≤ L/M ≤ 100 000 solar units). We identify the instability boundaries associated with low- to high-order radial oscillations (0 ≤ n ≤ 16). The instability boundaries are a strong function of both composition and radial order (n). With decreasing hydrogen abundance we find that (i) the classical blue edge of the Cepheid instability strip shifts to higher effective temperature and luminosity, and (ii) high-order modes are more easily excited and small islands of high radial-order instability develop, some of which correspond with real stars. Driving in all cases is by the classical κ-mechanism and/or strange modes. We identify regions of parameter space where new classes of pulsating variable may, in future, be discovered. The majority of these are associated with reduced hydrogen abundance in the envelope; one has not been identified previously.

  3. Cosmicflows-2: The Data

    CERN Document Server

    Tully, R Brent; Dolphin, Andrew E; Fisher, J Richard; Heraudeau, Philippe; Jacobs, Bradley A; Karachentsev, Igor D; Makarov, Dmitry; Makarova, Lidia; Mitronova, Sofia; Rizzi, Luca; Shaya, Edward J; Sorce, Jenny G; Wu, Po-Feng

    2013-01-01

    Cosmicflows-2 is a compilation of distances and peculiar velocities for over 8000 galaxies. Numerically the largest contributions come from the luminosity-linewidth correlation for spirals, the TFR, and the related Fundamental Plane relation for E/S0 systems, but over 1000 distances are contributed by methods that provide more accurate individual distances: Cepheid, Tip of the Red Giant Branch, Surface Brightness Fluctuation, SNIa, and several miscellaneous but accurate procedures. Our collaboration is making important contributions to two of these inputs: Tip of the Red Giant Branch and TFR. A large body of new distance material is presented. In addition, an effort is made to assure that all the contributions, our own and those from the literature, are on the same scale. Overall, the distances are found to be compatible with a Hubble Constant H_0 = 74.4 +-3.0 km/s/Mpc. The great interest going forward with this data set will be with velocity field studies. Cosmicflows-2 is characterized by a great density an...

  4. COSMICFLOWS-2: THE DATA

    Energy Technology Data Exchange (ETDEWEB)

    Tully, R. Brent; Courtois, Hélène M.; Jacobs, Bradley A.; Wu, Po-Feng [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, HI 96822 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E Hermans Rd., Tucson, AZ 85756 (United States); Fisher, J. Richard [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Héraudeau, Philippe [Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn (Germany); Karachentsev, Igor D.; Makarov, Dmitry; Makarova, Lidia; Mitronova, Sofia [Special Astrophysical Observatory, N Arkhyz, KChR 369167 (Russian Federation); Rizzi, Luca [W. M. Keck Observatory, 65-1120 Mamalahoa Highway, Waimea, HI 96743 (United States); Shaya, Edward J. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Sorce, Jenny G. [Université Claude Bernard Lyon I, Institut de Physique Nucleaire, F-69622 Lyon (France)

    2013-10-01

    Cosmicflows-2 is a compilation of distances and peculiar velocities for over 8000 galaxies. Numerically the largest contributions come from the luminosity-line width correlation for spirals, the Tully-Fisher relation (TFR), and the related fundamental plane relation for E/S0 systems, but over 1000 distances are contributed by methods that provide more accurate individual distances: Cepheid, tip of the red giant branch (TRGB), surface brightness fluctuation, Type Ia supernova, and several miscellaneous but accurate procedures. Our collaboration is making important contributions to two of these inputs: TRGB and TFR. A large body of new distance material is presented. In addition, an effort is made to ensure that all the contributions, both our own and those from the literature, are on the same scale. Overall, the distances are found to be compatible with a Hubble constant H {sub 0} = 74.4 ± 3.0 km s{sup –1} Mpc{sup –1}. The great interest going forward with this data set will be with velocity field studies. Cosmicflows-2 is characterized by a great density and high accuracy of distance measures locally, falling to sparse and coarse sampling extending to z = 0.1.

  5. Type Ia supernovae as extragalactic distance indicators

    CERN Document Server

    Branch, D; Fisher, A; Branch, David; Nugent, Peter; Fisher, Adam

    1996-01-01

    Because Type Ia supernovae (SNe Ia) are not perfect standard candles it is important to be able to use distance--independent observables (DIOs) to define subsets of SNe Ia that are ``nearly standard candles'' or to correct SN Ia absolute magnitudes to make them nearly homogeneous (``standardized candles''). This is not crucial for the measurement of H_0, but it is for the measurement of q_0 and of parent--galaxy peculiar velocities. We discuss the use of various photometric and spectroscopic SN Ia DIOs, and a parent--galaxy DIO, for this purpose. We also discuss the status of the absolute--magnitude calibration of SNe Ia. We find that SNe Ia, whether calibrated by means of (1) Cepheids in their parent galaxies, (2) fitting their optical--ultraviolet spectra with detailed non-LTE model atmosphere calculations, or (3) by considering that the light curve is powered by the decay of radioactive Ni, firmly indicate that the value of H_0 is low, less than or about 60 km/s/Mpc. Some issues regarding the determination...

  6. Spectroscopic Confirmation of the Dwarf Galaxies Hydra II and Pisces II and the Globular Cluster Laevens 1

    CERN Document Server

    Kirby, Evan N; Cohen, Judith G

    2015-01-01

    We present Keck/DEIMOS spectroscopy of stars in the recently discovered Milky Way satellites Hydra II, Pisces II, and Laevens 1. We measured a velocity dispersion of 5.4 (+3.6 -2.4) km/s for Pisces II, but we did not resolve the velocity dispersions of Hydra II or Laevens 1. We marginally resolved the metallicity dispersions of Hydra II and Pisces II but not Laevens 1. Furthermore, Hydra II and Pisces II obey the luminosity-metallicity relation for Milky Way dwarf galaxies ( = -2.02 +/- 0.08 and -2.45 +/- 0.07, respectively), whereas Laevens 1 does not ( = -1.68 +/- 0.05). The kinematic and chemical properties suggest that Hydra II and Pisces II are dwarf galaxies, and Laevens 1 is a globular cluster. We determined that two of the previously observed blue stars near the center of Laevens 1 are not members of the cluster. A third blue star has ambiguous membership. If it is a member, we suggest that it could be a Type II Cepheid variable. Hydra II has a radial velocity = 303.1 +/- 1.4 km/s, similar to the lea...

  7. Type Ia Supernovae and the Hubble Constant

    CERN Document Server

    Branch, D

    1998-01-01

    The focus of this review is the work that has been done during the 1990s on using Type Ia supernovae (SNe Ia) to measure the Hubble constant ($H_0$). SNe Ia are well suited for measuring $H_0$. A straightforward maximum-light color criterion can weed out the minority of observed events that are either intrinsically subluminous or substantially extinguished by dust, leaving a majority subsample that has observational absolute-magnitude dispersions of less than $\\sigma_{obs}(M_B) \\simeq \\sigma_{obs}(M_V) \\simeq 0.3$ mag. Correlations between absolute magnitude and one or more distance-independent SN Ia or parent-galaxy observables can be used to further standardize the absolute magnitudes to better than 0.2 mag. The absolute magnitudes can be calibrated in two independent ways --- empirically, using Cepheid-based distances to parent galaxies of SNe Ia, and physically, by light curve and spectrum fitting. At present the empirical and physical calibrations are in agreement at $M_B \\simeq M_V \\simeq -19.4$ or -19....

  8. A new estimate of the Local Standard of Rest from data on young Galactic objects

    CERN Document Server

    Bobylev, V V

    2014-01-01

    To estimate the peculiar velocity of the Sun with respect to the Local Standard of Rest (LSR), we used young objects in the Solar neighborhood with distance measurement errors within 10%-15%. These objects were the nearest Hipparcos stars of spectral classes O--B2.5, masers with trigonometric parallaxes measured by means of VLBI, and two samples of the youngest and middle-aged Cepheids. The most significant component of motion of all these stars is induced by the spiral density wave. As a result of using all these samples and taking into account the differential Galactic rotation, as well as the influence of the spiral density wave, we obtained the following components of the vector of the peculiar velocity of the Sun with respect to the LSR: (U_o,V_o,W_o)_{LSR}= (6.0,10.6,6.5)+/-(0.5,0.8,0.3) km s^{-1}. We have found that the Solar velocity components (U_o)_{LSR} and (V_o)_{LSR} are very sensitive to the Solar radial phase \\chi_o in the spiral density wave.

  9. The local standard of rest from data on young objects with account for the Galactic spiral density wave

    CERN Document Server

    Bobylev, Vadim

    2014-01-01

    To estimate the peculiar velocity of the Sun with respect to the Local Standard of Rest (LSR), we used young objects in the Solar neighborhood with distance measurement errors within 10%-15%. These objects were the nearest Hipparcos stars of spectral classes O-B2.5, masers with trigonometric parallaxes measured by means of VLBI, and two samples of the youngest and middle-aged Cepheids. The most significant component of motion of all these stars is induced by the spiral density wave. As a result of using all these samples and taking into account the differential Galactic rotation, as well as the influence of the spiral density wave, we obtained the following components of the vector of the peculiar velocity of the Sun with respect to the LSR: (Uo,Vo,Wo)_{LSR}=(6.0,10.6,6.5)+\\-(0.5,0.8,0.3) km/s. We have found that components of the Solar velocity are quite insensitive to errors of the distance Ro in a broad range of its values, from Ro=7.5 kpc to Ro=8.5 kpc, that affect the Galactic rotation curve parameters. ...

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

    International Nuclear Information System (INIS)

    We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two δ Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification. The pulsation properties of the RR Lyrae variables are close to those of Oosterhoff type II clusters, consistent with the low metal abundance and the cluster horizontal branch morphology, disfavoring (but not totally ruling out) an extragalactic hypothesis for the origin of NGC 2419. The observed properties of RR Lyrae and SX Phoenicis stars are used to estimate the cluster reddening and distance, using a number of different methods. Our final value is μ0 (NGC 2419) = 19.71 ± 0.08 mag (D = 87.5 ± 3.3 kpc), with E(B - V) = 0.08 ± 0.01 mag, [Fe/H] = -2.1 dex on the Zinn and West metallicity scale, and a value of MV that sets μ0 (LMC) = 18.52 mag. This value is in good agreement with the most recent literature estimates of the distance to NGC 2419.

  11. VizieR Online Data Catalog: ASAS 101538-5933.1 BV light curves (Berdnikov, 2013)

    Science.gov (United States)

    Berdnikov, L. N.

    2013-04-01

    In the plate collection of the Harvard College Observatory, we have obtained 528 photographic magnitude estimates for the recently discovered long-period classical Cepheid ASAS 101538-5933.1 (P=51.4-days). Together with the published photoelectric and CCD observations, our data have allowed us to construct an O-C diagram spanning a time interval of 120 years. The O-C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period, dP/dt=51.8(+/-4.8)s/yr or (dP/dt)/P=7.3(+/-0.7)s, in agreement with the results of theoretical calculations for the third crossing of the instability strip. The available data reduced by the method of Eddington and Plakidis reveal small random period fluctuations that do not distort the evolutionary trend in the O-C residuals. (1 data file).

  12. The pulsating variable star population in DDO210

    CERN Document Server

    Ordoñez, Antonio J

    2015-01-01

    We have probed the pulsating variable star content of the isolated Local Group dwarf galaxy, DDO210 (Aquarius), using archival Advanced Camera for Surveys/$Hubble$ $Space$ $Telescope$ imaging in the F475W and F814W passbands. We find a total of 32 RR Lyrae stars (24 ab-type, 8 c-type) and 75 Cepheid variables. The mean periods of the ab-type and c-type RR Lyrae stars are calculated to be $\\langle$P$_{\\mathrm{ab}}\\rangle = 0.609\\pm0.011$ and $\\langle$P$_{\\mathrm{c}}\\rangle = 0.359\\pm0.025$ days, respectively. The light curve properties of the fundamental mode RR Lyrae stars yield a mean metallicity of $\\langle$[Fe/H]$\\rangle$ = -1.63$\\pm$0.11 dex for this ancient population, consistent with a recent synthetic colour-magnitude diagram analysis. We find this galaxy to be Oosterhoff-intermediate and lacking in high-amplitude, short-period ab-type RR Lyrae, consistent with behavior recently observed for many dwarf spheroidals and ultra-faint dwarfs in the Local Group. We find a distance modulus of $\\mu = 25.07\\pm ...

  13. 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 ...

  14. OGLE Study of the Sagittarius Dwarf Spheroidal Galaxy and its M54 Globular Cluster

    CERN Document Server

    Hamanowicz, A; Udalski, A; Mroz, P; Soszynski, I; Szymanski, M K; Skowron, J; Poleski, R; Wyrzykowski, L; Kozlowski, S; Pawlak, M; Ulaczyk, K

    2016-01-01

    We use the fundamental-mode RR Lyr-type variable stars (RRab) from OGLE-IV to draw a 3D picture of the central part of the tidally disrupted Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. We estimate the line-of-sight thickness of the Sgr dSph stream to be 6sigma~6.2 kpc. Based on OGLE-IV observations collected in seasons 2011-2014 we conduct a comprehensive study of stellar variability in the field of the globular cluster M54 (NGC 6715) residing in the core of this dwarf galaxy. Among the total number of 270 detected variables we report the identification of 173 RR Lyr stars, 4 Type II Cepheids, 51 semi-regular variable red giants, 3 SX Phe-type stars, 18 eclipsing binary systems. Seventy-three variables are new discoveries. The distance to the cluster determined from RRab stars is d_M54=26.2+/-0.2_stat+/-1.3_sys kpc. From the location of RRab stars in the period-amplitude (Bailey) diagram we confirm the presence of two old populations, both in the cluster and the Sgr dSph stream.

  15. Clustering of local group distances: Publication bias or correlated measurements? II. M31 and beyond

    Energy Technology Data Exchange (ETDEWEB)

    De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Bono, Giuseppe [Dipartimento di Fisica, Università di Roma Tor Vergata, via Della Ricerca Scientifica 1, I-00133, Roma (Italy)

    2014-07-01

    The accuracy of extragalactic distance measurements ultimately depends on robust, high-precision determinations of the distances to the galaxies in the local volume. Following our detailed study addressing possible publication bias in the published distance determinations to the Large Magellanic Cloud (LMC), here we extend our distance range of interest to include published distance moduli to M31 and M33, as well as to a number of their well-known dwarf galaxy companions. We aim at reaching consensus on the best, most homogeneous, and internally most consistent set of Local Group distance moduli to adopt for future, more general use based on the largest set of distance determinations to individual Local Group galaxies available to date. Based on a careful, statistically weighted combination of the main stellar population tracers (Cepheids, RR Lyrae variables, and the magnitude of the tip of the red-giant branch), we derive a recommended distance modulus to M31 of (m−M){sub 0}{sup M31}=24.46±0.10 mag—adopting as our calibration an LMC distance modulus of (m−M){sub 0}{sup LMC}=18.50 mag—and a fully internally consistent set of benchmark distances to key galaxies in the local volume, enabling us to establish a robust and unbiased, near-field extragalactic distance ladder.

  16. The Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE): The Dust Extinction Curve in the Small Magellanic Cloud from Red Clump Stars

    Science.gov (United States)

    Yanchulova Merica-Jones, Petia; Sandstrom, Karin; Johnson, Lent C.; SMIDGE Team

    2016-06-01

    We present preliminary measurements of the average dust extinction curve in a 200 pc x 100 pc region in the Small Magellanic Cloud (SMC) using multi-band Hubble Space Telescope observations of resolved stellar populations from SMIDGE. Extinction curve determinations from a fully-sampled region of the SMC are of great interest. SMC-like extinction is widely used to correct for the effects of dust in low metallicity or high redshift galaxies, however, there are currently very few extinction curve measurements in the SMC. We measure the extinction curve using color-magnitude diagrams of red clump stars experiencing reddening by dust along a vector from which the curve shape can theoretically be directly measured. In addition, our analysis of the extincted and unextincted red clump stars shows a substantial line-of-sight depth for the stellar distribution of the SMC, consistent with recent observations of Cepheids. With the deep multi-band photometry from SMIDGE we are able to separate these two effects and measure both the extinction curve and the line-of-sight depth. Our study implies that extinction curve measurements in nearby galaxies need to take into account the impact of an extended galactic structure on dust extinction along the line of sight.

  17. Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

    Science.gov (United States)

    Britavskiy, Nikolay; Pancino, Elena; Romano, Donatella; Tsymbal, Vadim

    2015-08-01

    We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a Least Squares Deconvolution (LSD) of the line profiles in order to analyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (± 1 km/s) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 km/s even with a low number of high-resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

  18. PULSATION PERIOD VARIATIONS IN THE RRc LYRAE STAR KIC 5520878

    International Nuclear Information System (INIS)

    Learned et al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among variable stars using photometric data from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have found two such regimes of long and short pulse durations. The sequence of period lengths, expressed as time series data, is strongly autocorrelated, with correlation coefficients of prime numbers being significantly higher (p = 99.8%). Our analysis of this candidate star shows that the prime number oddity originates from two simultaneous pulsation periods and is likely of natural origin. Simple physical models elucidate the frequency content and asymmetries of the KIC 5520878 light curve. Despite this SETI null result, we encourage testing of other archival and future time-series photometry for signs of modulated stars. This can be done as a by-product to the standard analysis, and can even be partly automated

  19. 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.

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

    CERN Document Server

    Mondal, S; Chen, W P; 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; Marshal, S L; Protopapas, P; Rice, J A; Schwamb, M E; Wang, J -H; Wang, S -Y; Wen, C -Y

    2010-01-01

    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$^{\\rm h}30^{\\rm m}6\\fs$67, Dec = 27\\degr17\\arcmin 30\\arcsec, 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, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, delta Scuti, SX Phonencis, semi-regular and eclipsing binarie...

  1. VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way

    CERN Document Server

    Minniti, D; Emerson, J P; Saito, R K; Hempel, M; Pietrukowicz, P; Ahumada, A V; Alonso, M V; Alonso-García, J; Arias, J I; Bandyopadhyay, R M; Barbá, R H; Bedin, L R; Bica, E; Borissova, J; Bronfman, L; Catelan, M; Clariá, J J; Cross, N; de Grijs, R; Dékány, I; Drew, J E; Fariña, C; Feinstein, C; Lajús, E Fernández; Gamen, R C; Geisler, D; Gieren, W; Goldman, B; González, O; Gunthardt, G; Gurovich, S; Hambly, N C; Irwin, M J; Ivanov, V D; Jordán, A; Kerins, E; Kinemuchi, K; Kurtev, R; López-Corredoira, M; Maccarone, T; Masetti, N; Merlo, D; Messineo, M; Mirabel, I F; Monaco, L; Morelli, L; Padilla, N; Parisi, M C; Pignata, G; Rejkuba, M; Roman-Lopes, A; Sale, S E; Schreiber, M R; Schröder, A C; Smith, M; Sodré, L; Soto, M; Tamura, M; Tappert, C; Thompson, M A; Toledo, I; Zoccali, M

    2009-01-01

    We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 hours of observations with the 4-metre VISTA telescope during five years (2010-2014), covering ~10^9 point sources across an area of 520 deg^2, including 33 known globular clusters and ~350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9-2.5 microns) and a catalogue of more than 10^6 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete under...

  2. Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling

    CERN Document Server

    Moskalik, P; Kolenberg, K; Molnár, L; Kurtz, D W; Szabó, R; Benkő, J M; Nemec, J M; Chadid, M; Guggenberger, E; Ngeow, C -C; Jeon, Y -B; Kopacki, G; Kanbur, S M

    2014-01-01

    We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5yr. All four stars are found to be multiperiodic. The strongest secondary mode with frequency f_2 has an amplitude of a few mmag, 20 - 45 times lower than the main radial mode with frequency f_1. The two oscillations have a period ratio of P_2/P_1 = 0.612 - 0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is nonradial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P_2/P_1 ~ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f_2 at ~1/...

  3. The Hubble Space Telescope Key Project on the Extragalactic Distance Scale; 24, The Calibration of Tully-Fisher Relations and the Value of the Hubble Constant

    CERN Document Server

    Sakai, S; Hughes, S M G; Huchra, J P; Macri, L M; Kennicutt, R C; Gibson, B K; Ferrarese, L; Freedman, W L; Han, M; Ford, H C; Graham, J A; Illingworth, G D; Kelson, D D; Madore, B F; Sebo, K; Silbermann, N A; Stetson, P B; Sakai, Shoko; Mould, Jeremy R.; Hughes, Shaun M.G.; Huchra, John P.; Macri, Lucas M.; Kennicutt, Robert C.; Gibson, Brad K.; Ferrarese, Laura; Freedman, Wendy L.; Han, Mingsheng; Ford, Holland C.; Graham, John A.; Illingworth, Garth D.; Kelson, Daniel D.; Madore, Barry F.; Sebo, Kim; Silbermann, Nancy A.; Stetson, Peter B.

    1999-01-01

    This paper presents the calibration of BVRIH$ Tully-Fisher relations based on Cepheid distances to 21 galaxies within 25 Mpc, and 23 clusters within 10,000 km/s. These relations have been applied to several distant cluster surveys in order to derive a value for the Hubble constant, H0, mainly concentrating on an I-band all-sky survey by Giovanelli and collaborators which consisted of total I magnitudes and 50% linewidth data for ~550 galaxies in 16 clusters. For comparison, we also derive the values of H0 using surveys in B-band and V-band by Bothun and collaborators, and in H-band by Aaronson and collaborators. Careful comparisons with various other databases from literature suggest that the H-band data, whose magnitudes are isophotal magnitudes extrapolated from aperture magnitudes rather than total magnitudes, are subject to systematic uncertainties. Taking a weighted average of the estimates of Hubble constants from four surveys, we obtain H0 = 71 +- 4 (random) +- 7 (systematic) km/s/Mpc. We have also inv...

  4. Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields

    CERN Document Server

    Pietrukowicz, P; Mroz, P; Soszynski, I; Udalski, A; Poleski, R; Szymanski, M K; Kubiak, M; Pietrzynski, G; Wyrzykowski, L; Ulaczyk, K; Kozlowski, S; Skowron, J

    2013-01-01

    We present the results of a search for pulsating stars in the 7.12 deg^2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 14 Long-Period Variables, such as Miras and Semi-Regular Variables, and 56 very likely delta Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode delta Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5 M_sun and are located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. All reported pulsating variables but one object are new discoveries. They are included in the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going OGLE-IV Galactic Disk Survey, which covers half of the Galactic plane. For the purposes o...

  5. 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.

  6. Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium

    CERN Document Server

    Cescutti, G; François, P; Chiappini, C

    2006-01-01

    We model the abundance gradients in the disk of the Milky Way for several chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba, La and Eu), and compare our results with the most recent and homogeneous observational data. We adopt a chemical evolution model able to well reproduce the main properties of the solar vicinity. We compute, for the first time, the abundance gradients for all the above mentioned elements in the galactocentric distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in the galactocentric distance range 5-17 kpc gives a very good agreement for many of the studied elements. In addition, we fit very well the data for the evolution of Lanthanum in the solar vicinity for which we present results here for the first time. We explore, also for the first time, the behaviour of the abundance gradients at large galactocentric distances by comparing our results with data relative to distant open clusters and red giants and select the best chemical evol...

  7. RR Lyrae Stars in the Bootes dSph

    CERN Document Server

    Siegel, M H

    2006-01-01

    We present a catalog of 15 RR Lyrae variable stars in the recently discovered Bootes galaxy -- the most metal-poor simple stellar population with measured RR Lyrae stars. The pulsational properties of the RR Lyrae conform closely to period-abundance trends extrapolated from more metal-rich populations and we estimate the distance of Bootes to be (m-M)_0=18.96+-0.12. The average period (0.69 days), the ratio of type c to type ab pulsators (0.53) and the RRab period shift (-0.07) indicate an Oosterhoff II classification for Bootes, a marked contrast to the other dSph galaxies, which are Oosterhoff intermediate. This supports the contention that the Oosterhoff dichotomy is a continuum -- that RR Lyrae properties, to first order, vary smoothly with abundance. The dSph galaxies are not distinct from the Galactic globular clusters, but bridge the Oosterhoff gap. The absence of any anomalous Cepheids in Bootes could indicate the lack of an intermediate age population.

  8. SAGE-Var: An Infrared Survey of Variability in the Magellanic Clouds

    CERN Document Server

    Riebel, D; Srinivasan, S; Whitelock, P; Meixner, M; Babler, B; Feast, M; Groenewegen, M A T; Ita, Y; Meade, M; Shiao, B; Whitney, B

    2015-01-01

    We present the first results from the SAGE-Var program, a follow on to the Spitzer legacy program Surveying the Agents of Galaxy Evolution (SAGE; Meixner, et al. 2006). We obtained 4 epochs of photometry at 3.6 & 4.5 microns covering the bar of the Large Magellanic Cloud (LMC) and the central region of the Small Magellanic Cloud (SMC) in order to probe the variability of extremely red sources missed by variability surveys conducted at shorter wavelengths, and to provide additional epochs of observation for known variables. Our 6 total epochs of observations allow us to probe infrared variability on 15 different timescales ranging from ~20 days to ~5 years. Out of a full catalog of 1,717,554 (LMC) and 457,760 (SMC) objects, we find 10 (LMC) and 6 (SMC) large amplitude AGB variables without optically measured variability owing to circumstellar dust obscuration. The catalog also contains multiple observations of known AGB variables, type I and II Cepheids, eclipsing variables, R CrB stars and young stellar o...

  9. The multi-wavelength Tully-Fisher relation: hunting for the intrinsic scatter

    Science.gov (United States)

    Ponomareva, Anastasia

    2016-01-01

    The statistical properties of the Tully-Fisher relation provide important constraints for semi-analytical models and numerical simulations of galaxy formation and evolution. Over the past decades, the scatter in the Tully-Fisher relation has been decreased significantly by accurate photometric measures in the NIR bands. However, the small measurement errors on total luminosity can no longer explain the observed scatter. Therefore, we abandon the classical concept of the Tully-Fisher relation as a correlation using the width of global HI profile and consider instead the internal kinematics of gas in galaxies.As it is still not clear at which wavelengths the smallest scatter in the relation can be achieved, we assemble the Tully-Fisher relation for a calibrator sample of galaxies with measured TRGB/Cepheid distances over the broad wavelength range from FUV to 22 mm. We implement an improved kinematic measure by deriving high quality rotation curves, taking into account warps and streaming motions in the disk due to spiral arms or a bar.As a result, our studies show that besides the wavelength dependence, statistical properties of the Tully-Fisher relation are highly sensitive to the internal kinematics of gas.

  10. Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties

    CERN Document Server

    Brown, A G A; Prusti, T; de Bruijne, J; Mignard, F; Drimmel, R; co-authors, 585

    2016-01-01

    At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. We summarize Gaia DR1 and provide illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Gaia DR1 consists of: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set,consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ~3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about...

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

    International Nuclear Information System (INIS)

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

  12. Photometric study of the Blazhko star RZ Lyr

    CERN Document Server

    Jurcsik, J; Hajdu, G; Szeidl, B; Dózsa, Á; Posztobányi, K; Smitola, P; Belucz, B; Fehér, V; Kővári, Zs; Kriskovics, L; Kun, E; Molnár, L; Nagy, I; Vida, K; Görög, N

    2012-01-01

    The analysis of recent, extended multicolour CCD and archive photoelectric, photographic and visual observations has revealed several important properties of RZ Lyr, an RRab-type variable exhibiting large-amplitude Blazhko modulation. On the time-base of \\sim110 yr, a strict anticorrelation between the pulsation and modulation period changes is established. The light curve of RZ Lyr shows a remarkable bump on the descending branch in the small-amplitude phase of the modulation, similarly to the light curves of bump Cepheids. We speculate that the stellar structure temporally suits a 4:1 resonance between the periods of the fundamental and one of the higher-order radial modes in this modulation phase. The light-curve variation of RZ Lyr can be correctly fitted with a two-modulation-component solution; the 121 d period of the main modulation is nearly but not exactly four times longer than the period of the secondary modulation component. Using the inverse photometric method, the variations in the pulsation-ave...

  13. 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...

  14. The Carina Project IX: on Hydrogen and helium burning variables

    CERN Document Server

    Coppola, G; Stetson, P B; Bono, G; Braga, V F; Ripepi, V; Dall'Ora, M; Musella, I; Buonanno, R; Fabrizio, M; Ferraro, I; Fiorentino, G; Iannicola, G; Monelli, M; Nonino, M; Thévenin, F; Walker, R

    2015-01-01

    We present new multi-band (UBVI) time-series data of helium burning variables in the Carina dwarf spheroidal galaxy. The current sample includes 92 RR Lyrae-six of them are new identifications-and 20 Anomalous Cepheids, one of which is new identification. The analysis of the Bailey diagram shows that the luminosity amplitude of the first overtone component in double-mode variables is located along the long-period tail of regular first overtone variables, while the fundamental component is located along the short-period tale of regular fundamental variables. This evidence further supports the transitional nature of these objects. Moreover, the distribution of Carina double-mode variables in the Petersen diagram (P_1/P_0 vs P_0) is similar to metal-poor globulars (M15, M68), to the dwarf spheroidal Draco and to the Galactic Halo. This suggests that the Carina old stellar population is metal-poor and affected by a small spread in metallicity. We use trigonometric parallaxes for five field RR Lyrae stars to provi...

  15. A New Optical Polarization Catalog for the Small Magellanic Cloud: The Magnetic Field Structure

    CERN Document Server

    Gomes, Aiara Lobo; Pereyra, Antonio; Rodrigues, Cláudia Vilega

    2015-01-01

    We present a new optical polarimetric catalog for the Small Magellanic Cloud (SMC). It contains a total of 7207 stars, located in the Northeast (NE) and Wing sections of the SMC and part of the Magellanic Bridge. This new catalog is a significant improvement compared to previous polarimetric catalogs for the SMC. We used it to study the sky-projected interstellar magnetic field structure of the SMC. Three trends were observed for the ordered magnetic field direction at position angles of $(65 \\pm 10)$ deg, $(115 \\pm 10)$ deg, and $(150 \\pm 10)$ deg. Our results suggest the existence of an ordered magnetic field aligned with the Magellanic Bridge direction and SMC's Bar in the NE region, which have position angles roughly at $115.4$ deg and $45$ deg, respectively. However, the overall magnetic field structure is fairly complex. The trends at $115$ deg and $150$ deg may be correlated with the SMC's bimodal structure, observed in Cepheids' distances and HI velocities. We derived a value of $B_{sky} = (0.947 \\pm ...

  16. Testing Distance Estimators with the Fundamental Manifold

    Science.gov (United States)

    Zaritsky, Dennis; Zabludoff, Ann I.; Gonzalez, Anthony H.

    2012-03-01

    We demonstrate how the Fundamental Manifold (FM) can be used to cross-calibrate distance estimators even when those "standard candles" are not found in the same galaxy. Such an approach greatly increases the number of distance measurements that can be utilized to check for systematic distance errors and the types of estimators that can be compared. Here we compare distances obtained using Type Ia supernova (SN Ia), Cepheids, surface brightness fluctuations, the luminosity of the tip of the red giant branch, circumnuclear masers, eclipsing binaries, RR Lyrae stars, and the planetary nebulae luminosity functions. We find no significant discrepancies (differences are illustrate the use of FM distances to (1) revisit the question of the metallicity sensitivity of various estimators, confirming the dependence of SN Ia distances on host galaxy metallicity, and (2) provide an alternative calibration of H 0 that replaces the classical ladder approach in the use of extragalactic distance estimators with one that utilizes data over a wide range of distances simultaneously.

  17. Detection of the 128 day radial velocity variations in the supergiant {\\alpha} Persei. Rotational modulations, pulsations, or a planet?

    CERN Document Server

    Lee, Byeong-Cheol; Park, Myeong-Gu; Kim, Kang-Min; Mkrtichian, David E

    2012-01-01

    Aims. In order to search for and study the nature of the low-amplitude and long-periodic radial velocity (RV) variations of massive stars, we have been carrying out a precise RV survey for supergiants that lie near or inside the Cepheid instability strip. Methods. We have obtained high-resolution spectra of {\\alpha} Per (F5 Ib) from November 2005 to September 2011 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO). Results. Our measurements reveal that {\\alpha} Per shows a periodic RV variation of 128 days and a semi-amplitude of 70 m/s. We find no strong correlation between RV variations and bisector velocity span (BVS), but the 128-d peak is indeed present in the BVS variations among several other significant peaks in periodogram. Conclusions. {\\alpha} Per may have an exoplanet, but the combined data spanning over 20 years seem to suggest that the 128-d RV variations have not been stable on long-term scale, which is somewhat difficult to r...

  18. The light curves of the short-period variable stars in $\\Omega$ Centauri

    CERN Document Server

    Poretti, E

    1999-01-01

    The Fourier decomposition was applied to the light curves of the short period variable stars discovered by the OGLE team in Omega Cen. The phi_21 parameters are confined in a narrow strip for periods between 0.042 d and 0.07 d. Toward longer periods, there is an overlapping with the values obtained in the case of galactic stars. Toward shorter periods, the tendency to decreasing phi_21 values is also verified. A careful analysis should take more details in consideration: 1) Attention should be paid to the scatter in the distribution of the phi_21 parameters around 0.050 d. By analogy to Cepheid light curves, such a change can be the signature of a resonance between the fundamental mode and a higher overtone. 2) The small bunch of points above the progression at 0.038 d suggests a different light curve family. Since this group of stars shows a very small amplitude, it is possible that they are nonradial pulsators, not necessarily radial pulsators in a higher overtone. 3) The very low phi_21 value emphasizes th...

  19. Radial pulsation as a function of hydrogen abundance

    CERN Document Server

    Jeffery, C S

    2016-01-01

    Using linear non-adabatic pulsation analysis, we explore the radial-mode (p-mode) stability of stars across a wide range of mass (0.2 <= M <= 50 Msun), composition (0 <= X <= 0.7, Z=0.001, 0.02), effective temperature (3 000 <= T_eff <= 40 000 K), and luminosity (0.01 <= L/M <= 100,000 solar units).We identify the instability boundaries associated with low- to high-order radial oscillations (0 <= n <=16). The instability boundaries are a strong function of both composition and radial order (n). With decreasing hydrogen abundance we find that i) the classical blue edge of the Cepheid instability strip shifts to higher effective temperature and luminosity, and ii) high-order modes are more easily excited and small islands of high radial-order instability develop, some of which correspond with real stars. Driving in all cases is by the classical kappa-mechanism and/or strange modes. We identify regions of parameter space where new classes of pulsating variable may, in future, be dis...

  20. Radio Astronomers Set New Standard for Accurate Cosmic Distance Measurement

    Science.gov (United States)

    1999-06-01

    wavelength of the radio waves caused by the Doppler effect. The gas is orbiting at a speed of more than two million miles per hour. The orbiting disk of gas is almost edge-on as viewed from Earth. The astronomers obtained the orbital speeds and the positions of the masers in the disk by measuring the Doppler Shift of the masers at the disk's sides, where the gas is moving almost directly away from the Earth on one side and toward the Earth on the other. Measurements of the different orbital speeds at different distances from the black hole, made in 1994, allowed them to determine the mass of the black hole. These measurements required the great resolving power, or ability to see fine detail, of the VLBA. This picture of an orbiting disk was confirmed by measurement of centrifugal acceleration, according to the scientists. The newest observations were focused on maser "spots" on the near edge of the disk, where orbital motion shifts their position in the sky, though by an extremely small amount. The VLBA, however, was able to detect this extremely small movement, called "proper motion" by astronomers. This motion was detected by observing the galaxy at 4- to 8-month intervals over more than three years. "By knowing the speed at which the gas is orbiting and then measuring its motion across the sky, we can use plain old trigonometry to calculate the distance," Greenhill said. He added, however, that "you need a bit of luck to be able to do this. So far, we know of only 22 galaxies with water masers in their nuclear regions that also are relatively nearby. Then, the geometry of the disk, relative to Earth, has to be right to allow us to make such a measurement" The VLBA measurement of NGC 4258's distance differs significantly from the distance to that galaxy determined through HST observations of Cepheid variable stars. Using such stars, a team of astronomers led by University of California-Berkeley scientist Eyal Maoz has made preliminary and as-yet unpublished estimates of

  1. Photospheric magnitude diagrams for type II supernovat: A promising tool to compute distances

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez, Ósmar; Clocchiatti, Alejandro; Hamuy, Mario, E-mail: olrodrig@astro.puc.cl [Millennium Institute of Astrophysics, Casilla 36-D, Santiago (Chile)

    2014-12-01

    We develop an empirical color-based standardization for Type II supernovae (SNe II), equivalent to the classical surface brightness method given in Wesselink. We calibrate this standardization using SNe II with host galaxy distances measured using Cepheids, and a well-constrained shock breakout epoch and extinction due to the host galaxy. We estimate the reddening with an analysis of the B – V versus V – I color-color curves, similar to that of Natali et al. With four SNe II meeting the above requirements, we build a photospheric magnitude versus color diagram (similar to an H-R diagram) with a dispersion of 0.29 mag. We also show that when using time since shock breakout instead of color as the independent variable, the same standardization gives a dispersion of 0.09 mag. Moreover, we show that the above time-based standardization corresponds to the generalization of the standardized candle method of Hamuy and Pinto for various epochs throughout the photospheric phase. To test the new tool, we construct Hubble diagrams for different subsamples of 50 low-redshift (cz < 10{sup 4} km s{sup –1}) SNe II. For 13 SNe within the Hubble flow (cz {sub CMB} > 3000 km s{sup –1}) and with a well-constrained shock breakout epoch we obtain values of 68-69 km s{sup –1} Mpc{sup –1} for the Hubble constant and a mean intrinsic scatter of 0.12 mag or 6% in relative distances.

  2. Extended-Spectrum β-Lactamases and/or Carbapenemases-Producing Enterobacteriaceae Isolated from Retail Chicken Meat in Zagazig, Egypt.

    Directory of Open Access Journals (Sweden)

    H M Abdallah

    Full Text Available The aim of the present study was to determine the prevalence and to characterize extended-spectrum β-lactamases- and/or carbapenemases-producing Enterobacteriaceae among Enterobacteriaceae isolated from retail chicken meat in Zagazig, Egypt.One hundred and six Enterobacteriaceae isolates were collected from retail chicken meat samples purchased in Zagazig, Egypt in 2013. Species identification was done by MALDI-TOF MS. Screening for ESBL-E was performed by inoculation of isolates recovered from meat samples onto the EbSA (Cepheid Benelux, Apeldoorn, the Netherlands selective screening agar. ESBL production was confirmed by combination disc diffusion test with clavulanic acid (Rosco, Taastrup, Denmark. Carbapenemases production was confirmed with double disk synergy tests. Resistance genes were characterized by PCR with specific primers for TEM, SHV, and CTX-M and carbapenemases (KPC, NDM, OXA-48, IMP and VIM. PCR products of CTX-M genes were purified and sequenced. Phylogenetic grouping of E. coli was performed by a PCR-based method.Of these 106 isolates 69 (65.09% were ESBL producers. Twelve (11.32% of these isolates were also phenotypically class B carbapenemases producer. TEM genes were detected in 61 (57.55% isolates. 49 (46.23% isolates harbored CTX-M genes, and 25 (23.58% carried genes of the SHV family. All CPE belonged to the NDM group. The predominant CTX-M sequence type was CTX-M-15 (89.80%. The majority (80% of the ESBL-EC belonged to low virulence phylogroups A and B1.This is the first study from Egypt reporting high rates of ESBLs and carbapenemases (65.09% and 11.32%, respectively in Enterobacteriaceae isolated from retail chicken meat. These results raise serious concerns about public health and food safety as retail meat could serve as a reservoir for these resistant bacteria which could be transferred to humans through the food chain.

  3. Eclipsing binary stars in the Large Magellanic Cloud: results from the EROS-2, OGLE and VMC surveys

    Science.gov (United States)

    Muraveva, T.; Clementini, G.; Maceroni, C.; Evans, C. J.; Moretti, M. I.; Cioni, M.-R. L.; Marquette, J. B.; Ripepi, V.; de Grijs, R.; Groenewegen, M. A. T.; Piatti, A. E.; van Loon, J. Th.

    2014-09-01

    We present a catalogue of 1768 eclipsing binary stars (EBs) detected in the Large Magellanic Cloud (LMC) by the second generation of the EROS survey (hereinafter EROS-2); 493 of them are new discoveries located in outer regions (out of the central bar) of the LMC. These sources were originally included in a list of candidate classical Cepheids (CCs) extracted from the EROS-2 catalogue on the basis of the period (0.89 < 17.82 mag] diagram. After visual inspection of the light curves we reclassified them as eclipsing binaries. They have blue colours (BEROS - REROS < 0.2 mag) hence we classed them as hot eclipsing binaries (HEBs) containing hot massive components: main sequence (MS) stars or blue giants. We present Ks-band light curves for 999 binaries from our sample that have a counterpart in the VISTA near-infrared ESO public survey of the Magellanic Clouds system (VMC). We provide spectral classifications of 13 HEBs with existing spectroscopy. We divided our sample into contact-like binaries and detached/semi-detached systems based on both visual inspection and the parameters of the Fourier decomposition of the light curves and analysed the period-luminosity (PL) relations of the contact-like systems using the REROS and Ks magnitudes at maximum light. The contact-like binaries in our sample do not follow PL relations. We analysed the sample of contact binaries from the OGLE III catalogue and confirmed that PLI and PL_{K_s} sequences are defined only by eclipsing binaries containing a red giant component.

  4. Periods of ZZ Ceti variables

    International Nuclear Information System (INIS)

    White dwarf pulsators (ZZ Ceti variables) osub solar acccur in the extension of the radial pulsation envelope ionization instability strip to the observed luminosities of 3 x 10-3L sub solar according to van Horn. Investigations were underway to see if the driving mechanisms of hydrogen and helium ionization can cause radial pulsations as they do for the Cepheids, the RR Lyrae variables, and the delta Scuti variables. Masses used in this study are 0.60 and 0.75 M sub solar for T/sub e/ between 10,000 K and 14,000 K, the observed range in T/sub e/. Helium rich surface compositions like Y = 0.78,, Z = 0.02 as well as Y = 0.28, Z = 0.02 were used in spite of observations showing only hydrogen lines in the spectrum. The deep layers are pure carbon, and several transition compositions are included. The models show radial pulsation instabilities for many overtone modes at periods between about 0.3 and 3 seconds. The driving mechanism is mostly helium ionization at 40,000 and 150,000 K. The blue edge at about 14,000 K is probably due to the driving region becoming too shallow, and the red edge at 10,000 K is due to so much convection in the pulsation deriving region that no radiative luminosity is available for modulation by the γ and kappa effects. It is speculated that the very long observed periods (100 to 1000 sec) of ZZ Ceti variables are not due to nonradial pulsations, but are possibly aliases due to data undersampling. 4 references

  5. THE CARINA PROJECT. VI. THE HELIUM-BURNING VARIABLE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Coppola, G.; Marconi, M.; Ripepi, V.; Dall' Ora, M.; Musella, I. [INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli (Italy); Stetson, P. B. [Dominion Astrophysical Observatory, NRC-Herzberg, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Bono, G.; Buonanno, R. [Dipartimento di Fisica-Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy); Fabrizio, M. [INAF-Osservatorio Astronomico di Collurania, via M. Maggini, I-64100 Teramo (Italy); Ferraro, I.; Iannicola, G.; Pulone, L. [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Italy); Fiorentino, G. [INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy); Monelli, M. [Instituto de Astrofisica de Canarias, Calle Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain); Nonino, M. [INAF-Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, I-40131 Trieste (Italy); Thevenin, F. [Universite de Nice-Sophia Antipolis, Lab. Lagrange, UMR 7293, Observatoire de la Cote dAzur, BP 4229, F-06304 Nice (France); Walker, A. R., E-mail: coppola@na.astro.it [Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile)

    2013-09-20

    We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, 4 are Anomalous Cepheids (ACs), and 2 are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dwarf spheroidal galaxies and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We use the BV Period-Wesenheit (PW) relation of RRLs together with evolutionary prescriptions and find a true distance modulus of 20.09 {+-} 0.07 (intrinsic) {+-} 0.1 (statistical) mag that agrees quite well with similar estimates available in the literature. We identified four peculiar variables. Taking into account their position in the Bailey diagram and in the BV PW relation, two of them (V14 and V149) appear to be candidate ACs, while two (V158 and V182) might be peculiar RRLs. In particular, the variable V158 has a period and a V-band amplitude very similar to the low-mass RRL-RRLR-02792-recently identified by Pietrzynski et al. in the Galactic bulge.

  6. 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.

  7. Development of a Data Reduction Pipeline to Measure Stellar Radial Velocities Using Kutztown University's On-Campus Research Observatory

    Science.gov (United States)

    Fox, Odysseus; Reed, Phillip A.

    2016-01-01

    The Kutztown University Observatory (KUO) houses a 0.6m Ritchey-Chrétien telescope with a focal ratio of f/8. It is a dedicated observatory collecting data every clear night using the eShel model (Shelyak Instruments) echelle spectrograph. The spectral resolution is R = 11,000 and the final dispersion is 0.050 Å/pixel over the range of 4300 Å to 8100 Å.It is paramount to ensure accurate radial velocity (RV) measurements when conducting projects for research and education. RV measurements at KUO are used to determine the masses of spectroscopic binary stars, study pulsations of stellar photospheres (Cepheid variables), and to perform reconnaissance RV measurements of exoplanet candidates (reflex motion of host star).We present a data reduction pipeline program that produces RV measurements from observed spectra. After using the eShel's built in ThAr lamp for wavelength calibration, the program continuum normalizes the spectrum, creates a non-moving template (synthetic and/or observed spectrum), and corrects for barycentric motion. Finally, the program performs a cross correlation of the data and template to produce accurate RV measurements.Examples of completed and on-going projects at KUO are presented. We also demonstrate our ability to observe stellar RV's with uncertainties as good as 0.13 km/s. The eShel spectrograph is commercially available and is becoming popular among users of smaller telescopes. This data reduction pipeline will be useful to the increasing number of researchers utilizing the eShel spectrograph.

  8. Precision Photometry of Long Period Variable Stars: Flares and Bumps in the Night (Poster abstract)

    Science.gov (United States)

    Mais, D.

    2015-06-01

    (Abstract only) Mira variable stars are a broad class of stars, which encompass spectroscopic classes of type M, S, and C. These stars are closely related in terms of their long term variability, position on the Hertzsprung-Russell diagram their intermediate mass (from ~0.8 to ~8 solar mass) and the fact that class M evolves into the S and C type stars as certain stages of shell burning around the core proceeds. Recently, evidence has accumulated to suggest that Mira variables may go through flare up stages which result in brightening on the order of several tenths of a magnitude or more and may last hours to days in length. Very little is known about these events, indeed it is not clear that these events are real. In order to address the reality of these events, we established an automated acquisition/analysis of a group of 108 Mira variables in order to obtain the densest coverage of the periods to better constrain the potential flare-ups. Telescope control scripts were put in place along with real time analysis. This allowed for unattended acquisition of data on every clear night, all night long, in the V, R, and I photometric bands. In addition, during the course of the night multiple determinations are often obtained for a given star. The light curves of many of the program stars show a Cepheid-like bump phenomenon, however these appear on the ascending part of the light curve. In general, these bumps appear in longer period Mira's (>350 days). Bumps are not obvious or easily seen in VISUAL data records, although slope changes during rising phase are seen in some cases. So far, greater than 100,000 magnitude determinations have been obtained, many closely spaced in time. This should help to further constrain the potential occurrences of flare-up events.

  9. Stellar Archeology in the Galactic Halo with Ultra-faint Dwarfs. VII. Hercules

    Science.gov (United States)

    Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella; Clementini, Gisella; Dall'Ora, Massimo; Scowcroft, Victoria; Moretti, Maria Ida; Di Fabrizio, Luca; Greco, Claudia; Coppola, Giuseppina; Bersier, David; Catelan, Márcio; Grado, Aniello; Limatola, Luca; Smith, Horace A.; Kinemuchi, Karen

    2012-09-01

    We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, langP abrang = 0.68 days (σ = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 ± 0.15 dex, E(B - V) = 0.09 ± 0.02 mag, and (m - M)0 = 20.6 ± 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V ~ 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' × 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68. Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma, Canary Islands, Spain, at the 4.2 m William Herschel Telescope, Roche de los Muchachos, Canary Islands, Spain, at the 2.2 m ESO/MPI telescope, La Silla, Chile, Proposal 079.D-0587, at the 2 m Liverpool Telescope, Roche de los Muchachos, Canary Islands, Spain, and at the 2 m Faulkes Telescope North, Haleakala Observatory, Hawaii, USA.

  10. Availability of an assay for detecting Mycobacterium tuberculosis, including rifampin-resistant strains, and considerations for its use - United States, 2013.

    Science.gov (United States)

    2013-10-18

    In August 2013, the Food and Drug Administration (FDA) permitted marketing of the Xpert MTB/RIF assay (Cepheid, Sunnyvale, California) to detect DNA of the Mycobacterium tuberculosis complex (MTBC) and genetic mutations associated with resistance to rifampin (RMP) in unprocessed sputum and concentrated sputum sediments. Along with clinical, radiographic, and other laboratory findings, results of the assay aid in the diagnosis of pulmonary tuberculosis (TB). The assay is a nucleic acid amplification-based (NAA)* test using a disposable cartridge in conjunction with the GeneXpert Instrument System. Sensitivity and specificity of the Xpert MTB/RIF assay for detection of MTBC appear to be comparable with other FDA-approved NAA assays for this use, although direct comparison studies have not been performed. Sensitivity of detection of RMP resistance was 95% and specificity 99% in a multicenter study using archived and prospective specimens from subjects aged ≥18 years suspected of having TB who had 0-3 days of antituberculous treatment. CDC continues to recommend following published U.S. guidelines for TB diagnosis and infection control practice, including the use and interpretation of NAA test results. Providers and laboratories need to ensure that specimens are available for other recommended mycobacteriological testing. The Xpert MTB/RIF assay aids in the prompt diagnosis of TB and RMP-resistant disease. RMP resistance most often coexists with isoniazid (INH) resistance; TB that is resistant to both drugs is multidrug-resistant (MDR)† TB. Because the prevalence of RMP resistance is low in the United States (about 1.8% of TB cases), a positive result indicating a mutation in the rpoB gene of MTBC should be confirmed by rapid DNA sequencing for prompt reassessment of the treatment regimen and followed by growth-based drug susceptibility testing (DST). CDC offers these services free of charge.§ PMID:24141407

  11. VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way

    Science.gov (United States)

    Minniti, D.; Lucas, P. W.; Emerson, J. P.; Saito, R. K.; Hempel, M.; Pietrukowicz, P.; Ahumada, A. V.; Alonso, M. V.; Alonso-Garcia, J.; Arias, J. I.; Bandyopadhyay, R. M.; Barbá, R. H.; Barbuy, B.; Bedin, L. R.; Bica, E.; Borissova, J.; Bronfman, L.; Carraro, G.; Catelan, M.; Clariá, J. J.; Cross, N.; de Grijs, R.; Dékány, I.; Drew, J. E.; Fariña, C.; Feinstein, C.; Fernández Lajús, E.; Gamen, R. C.; Geisler, D.; Gieren, W.; Goldman, B.; Gonzalez, O. A.; Gunthardt, G.; Gurovich, S.; Hambly, N. C.; Irwin, M. J.; Ivanov, V. D.; Jordán, A.; Kerins, E.; Kinemuchi, K.; Kurtev, R.; López-Corredoira, M.; Maccarone, T.; Masetti, N.; Merlo, D.; Messineo, M.; Mirabel, I. F.; Monaco, L.; Morelli, L.; Padilla, N.; Palma, T.; Parisi, M. C.; Pignata, G.; Rejkuba, M.; Roman-Lopes, A.; Sale, S. E.; Schreiber, M. R.; Schröder, A. C.; Smith, M.; , L. Sodré, Jr.; Soto, M.; Tamura, M.; Tappert, C.; Thompson, M. A.; Toledo, I.; Zoccali, M.; Pietrzynski, G.

    2010-07-01

    We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 h of observations with the 4-m VISTA telescope during 5 years (2010-2014), covering ˜10 9 point sources across an area of 520 deg 2, including 33 known globular clusters and ˜350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9-2.5 μm) and a catalogue of more than 10 6 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete understanding of the variable sources in the inner Milky Way. This public survey will provide data available to the whole community and therefore will enable further studies of the history of the Milky Way, its globular cluster evolution, and the population census of the Galactic Bulge and center, as well as the investigations of the star forming regions in the disk. The combined variable star catalogues will have important implications for theoretical investigations of pulsation properties of stars.

  12. The spiral structure of the Galaxy revealed by CS sources and evidence for the 4:1 resonance

    Science.gov (United States)

    Lépine, J. R. D.; Roman-Lopes, A.; Abraham, Zulema; Junqueira, T. C.; Mishurov, Yu. N.

    2011-06-01

    We present a map of the spiral structure of the Galaxy, as traced by molecular carbon monosulphide (CS) emission associated with IRAS sources which are believed to be compact H II regions. The CS line velocities are used to determine the kinematic distances of the sources in order to investigate their distribution in the galactic plane. This allows us to use 870 objects to trace the arms, a number larger than that of previous studies based on classical H II regions. The distance ambiguity of the kinematic distances, when it exists, is solved by different procedures, including the latitude distribution and an analysis of the longitude-velocity diagram. The study of the spiral structure is complemented with other tracers: open clusters, Cepheids, methanol masers and H II regions. The well-defined spiral arms are seen to be confined inside the corotation radius, as is often the case in spiral galaxies. We identify a square-shaped sub-structure in the CS map with that predicted by stellar orbits at the 4:1 resonance (four epicycle oscillations in one turn around the galactic centre). The sub-structure is found at the expected radius, based on the known pattern rotation speed and epicycle frequency curve. An inner arm presents an end with strong inwards curvature and intense star formation that we tentatively associate with the region where this arm surrounds the extremity of the bar, as seen in many barred galaxies. Finally, a new arm with concave curvature is found in the Sagitta to Cepheus region of the sky. The observed arms are interpreted in terms of perturbations similar to grooves in the gravitational potential of the disc, produced by crowding of stellar orbits.

  13. Clustering of local group distances: publication bias or correlated measurements? I. The large Magellanic cloud

    Energy Technology Data Exchange (ETDEWEB)

    De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Wicker, James E. [National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China); Bono, Giuseppe [Dipartimento di Fisica, Università di Roma Tor Vergata, via Della Ricerca Scientifica 1, I-00133 Roma (Italy)

    2014-05-01

    The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly—and with a small spread—around the 'canonical' distance modulus, (m – M){sub 0} = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m – M){sub 0} = 18.49 ± 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent.

  14. Optical interferometry in astronomy

    International Nuclear Information System (INIS)

    Here I review the current state of the field of optical stellar interferometry, concentrating on ground-based work although a brief report of space interferometry missions is included. We pause both to reflect on decades of immense progress in the field as well as to prepare for a new generation of large interferometers just now being commissioned (most notably, the CHARA, Keck and VLT Interferometers). First, this review summarizes the basic principles behind stellar interferometry needed by the lay-physicist and general astronomer to understand the scientific potential as well as technical challenges of interferometry. Next, the basic design principles of practical interferometers are discussed, using the experience of past and existing facilities to illustrate important points. Here there is significant discussion of current trends in the field, including the new facilities under construction and advanced technologies being debuted. This decade has seen the influence of stellar interferometry extend beyond classical regimes of stellar diameters and binary orbits to new areas such as mapping the accretion discs around young stars, novel calibration of the cepheid period-luminosity relation, and imaging of stellar surfaces. The third section is devoted to the major scientific results from interferometry, grouped into natural categories reflecting these current developments. Lastly, I consider the future of interferometry, highlighting the kinds of new science promised by the interferometers coming on-line in the next few years. I also discuss the longer-term future of optical interferometry, including the prospects for space interferometry and the possibilities of large-scale ground-based projects. Critical technological developments are still needed to make these projects attractive and affordable

  15. Self-oscillation

    Science.gov (United States)

    Jenkins, Alejandro

    2013-04-01

    Physicists are very familiar with forced and parametric resonance, but usually not with self-oscillation, a property of certain dynamical systems that gives rise to a great variety of vibrations, both useful and destructive. In a self-oscillator, the driving force is controlled by the oscillation itself so that it acts in phase with the velocity, causing a negative damping that feeds energy into the vibration: no external rate needs to be adjusted to the resonant frequency. The famous collapse of the Tacoma Narrows bridge in 1940, often attributed by introductory physics texts to forced resonance, was actually a self-oscillation, as was the swaying of the London Millennium Footbridge in 2000. Clocks are self-oscillators, as are bowed and wind musical instruments. The heart is a “relaxation oscillator”, i.e., a non-sinusoidal self-oscillator whose period is determined by sudden, nonlinear switching at thresholds. We review the general criterion that determines whether a linear system can self-oscillate. We then describe the limiting cycles of the simplest nonlinear self-oscillators, as well as the ability of two or more coupled self-oscillators to become spontaneously synchronized (“entrained”). We characterize the operation of motors as self-oscillation and prove a theorem about their limit efficiency, of which Carnot’s theorem for heat engines appears as a special case. We briefly discuss how self-oscillation applies to servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business cycle, among other applications. Our emphasis throughout is on the energetics of self-oscillation, often neglected by the literature on nonlinear dynamical systems.

  16. THE DISTANCE TO M101 HOSTING TYPE Ia SUPERNOVA 2011fe BASED ON THE TIP OF THE RED GIANT BRANCH

    International Nuclear Information System (INIS)

    We present a new determination of the distance to M101, host of the Type Ia supernova (SN Ia) 2011fe, based on the tip of the red giant branch (TRGB) method. Our determination is based on Hubble Space Telescope archival F555W and F814W images of nine fields within the galaxy. Color-magnitude diagrams of arm-free regions in all fields show a prominent red giant branch. We measure the I-band magnitudes of the TRGB, obtaining a mean value of ITRGB = 25.28 ± 0.01 (where the error is a standard error), using an edge-detection method. We derive a weighted mean value of distance modulus (m – M)0 = 29.30 ± 0.01(random) ± 0.12(systematic), corresponding to a linear distance of 7.24 ± 0.03 ± 0.40 Mpc. While previous estimates for M101 show a large range (TRGB distances of (m – M)0 = 29.05-29.42 and Cepheid distances of (m – M)0 = 29.04-29.71), our measurements of the TRGB distances for nine fields show a small dispersion of only 0.02. We combine our distance estimate and photometry in the literature to derive absolute peak magnitudes in optical and near-infrared bands of SN 2011fe. Absolute maximum magnitudes of SN 2011fe are ∼0.2 mag brighter in the optical band and much more in the NIR than the current calibrations of SNe Ia in the literature. From the optical maximum magnitudes of SN 2011fe we obtain a value of the Hubble constant, H0 = 65.0 ± 0.5(random) ± 5.7(systematic) km s–1 Mpc–1, slightly smaller than other recent determinations of H0.

  17. Interstellar extinction curve variations towards the inner Milky Way: a challenge to observational cosmology

    Science.gov (United States)

    Nataf, David M.; Gonzalez, Oscar A.; Casagrande, Luca; Zasowski, Gail; Wegg, Christopher; Wolf, Christian; Kunder, Andrea; Alonso-Garcia, Javier; Minniti, Dante; Rejkuba, Marina; Saito, Roberto K.; Valenti, Elena; Zoccali, Manuela; Poleski, Radosław; Pietrzyński, Grzegorz; Skowron, Jan; Soszyński, Igor; Szymański, Michał K.; Udalski, Andrzej; Ulaczyk, Krzysztof; Wyrzykowski, Łukasz

    2016-03-01

    We investigate interstellar extinction curve variations towards ˜4 deg2 of the inner Milky Way in VIJKs photometry from the OGLE-III (third phase of the Optical Gravitational Lensing Experiment) and VVV (VISTA Variables in the Via Lactea) surveys, with supporting evidence from diffuse interstellar bands and F435W, F625W photometry. We obtain independent measurements towards ˜2000 sightlines of AI, E(V - I), E(I - J) and E(J - Ks), with median precision and accuracy of 2 per cent. We find that the variations in the extinction ratios AI/E(V - I), E(I - J)/E(V - I) and E(J - Ks)/E(V - I) are large (exceeding 20 per cent), significant and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve have at least two degrees of freedom, and not one (e.g. RV), which we confirm with a principal component analysis. We derive a median value of = 13.44, which is ˜60 per cent higher than the `standard' value. We show that the Wesenheit magnitude WI = I - 1.61(I - J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of Type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ˜100 per cent and lack sensitivity to extinction curve variations.

  18. Cost-Effectiveness of Automated Digital Microscopy for Diagnosis of Active Tuberculosis.

    Directory of Open Access Journals (Sweden)

    Swati Jha

    Full Text Available Automated digital microscopy has the potential to improve the diagnosis of tuberculosis (TB, particularly in settings where molecular testing is too expensive to perform routinely. The cost-effectiveness of TB diagnostic algorithms using automated digital microscopy remains uncertain.Using data from a demonstration study of an automated digital microscopy system (TBDx, Applied Visual Systems, Inc., we performed an economic evaluation of TB diagnosis in South Africa from the health system perspective. The primary outcome was the incremental cost per new TB diagnosis made. We considered costs and effectiveness of different algorithms for automated digital microscopy, including as a stand-alone test and with confirmation of positive results with Xpert MTB/RIF ('Xpert', Cepheid, Inc.. Results were compared against both manual microscopy and universal Xpert testing.In settings willing to pay $2000 per incremental TB diagnosis, universal Xpert was the preferred strategy. However, where resources were not sufficient to support universal Xpert, and a testing volume of at least 30 specimens per day could be ensured, automated digital microscopy with Xpert confirmation of low-positive results could facilitate the diagnosis of 79-84% of all Xpert-positive TB cases, at 50-60% of the total cost. The cost-effectiveness of this strategy was $1280 per incremental TB diagnosis (95% uncertainty range, UR: $340-$3440 in the base case, but improved under conditions likely reflective of many settings in sub-Saharan Africa: $677 per diagnosis (95% UR: $450-$935 when sensitivity of manual smear microscopy was lowered to 0.5, and $956 per diagnosis (95% UR: $40-$2910 when the prevalence of multidrug-resistant TB was lowered to 1%.Although universal Xpert testing is the preferred algorithm for TB diagnosis when resources are sufficient, automated digital microscopy can identify the majority of cases and halve the cost of diagnosis and treatment when resources are more

  19. STELLAR ARCHEOLOGY IN THE GALACTIC HALO WITH ULTRA-FAINT DWARFS. VII. HERCULES

    Energy Technology Data Exchange (ETDEWEB)

    Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella, E-mail: ilaria@na.astro.it, E-mail: ripepi@na.astro.it, E-mail: marcella@na.astro.it [INAF, Osservatorio Astronomico di Capodimonte, I-8013 Napoli (Italy); and others

    2012-09-10

    We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, (P{sub ab}) = 0.68 days ({sigma} = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 {+-} 0.15 dex, E(B - V) = 0.09 {+-} 0.02 mag, and (m - M){sub 0} = 20.6 {+-} 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V {approx} 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' Multiplication-Sign 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68.

  20. High-precision photometry for K2 Campaign 1

    Science.gov (United States)

    Huang, C. X.; Penev, K.; Hartman, J. D.; Bakos, G. Á.; Bhatti, W.; Domsa, I.; de Val-Borro, M.

    2015-12-01

    The two reaction wheel K2 mission promises and has delivered new discoveries in the stellar and exoplanet fields. However, due to the loss of accurate pointing, it also brings new challenges for the data reduction processes. In this paper, we describe a new reduction pipeline for extracting high-precision photometry from the K2 data set, and present public light curves for the K2 Campaign 1 target pixel data set. Key to our reduction is the derivation of global astrometric solutions from the target stamps, from which accurate centroids are passed on for high-precision photometry extraction. We extract target light curves for sources from a combined UCAC4 and EPIC catalogue - this includes not only primary targets of the K2 campaign 1, but also any other stars that happen to fall on the pixel stamps. We provide the raw light curves, and the products of various detrending processes aimed at removing different types of systematics. Our astrometric solutions achieve a median residual of ˜0.127 arcsec. For bright stars, our best 6.5 h precision for raw light curves is ˜20 parts per million (ppm). For our detrended light curves, the best 6.5 h precision achieved is ˜15 ppm. We show that our detrended light curves have fewer systematic effects (or trends, or red-noise) than light curves produced by other groups from the same observations. Example light curves of transiting planets and a Cepheid variable candidate, are also presented. We make all light curves public, including the raw and detrended photometry, at http://k2.hatsurveys.org.

  1. Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling

    Science.gov (United States)

    Moskalik, P.; Smolec, R.; Kolenberg, K.; Molnár, L.; Kurtz, D. W.; Szabó, R.; Benkő, J. M.; Nemec, J. M.; Chadid, M.; Guggenberger, E.; Ngeow, C.-C.; Jeon, Y.-B.; Kopacki, G.; Kanbur, S. M.

    2015-03-01

    We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5 yr. All four stars are found to be multiperiodic. The strongest secondary mode with frequency f2 has an amplitude of a few mmag, 20-45 times lower than the main radial mode with frequency f1. The two oscillations have a period ratio of P2/P1 = 0.612-0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is non-radial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P2/P1 ˜ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f2 at ˜1/2f2 and at ˜3/2f2. This is a signature of period doubling of the secondary oscillation, and is the first detection of period doubling in RRc stars. The amplitudes and phases of f2 and its subharmonics are variable on a time-scale of 10-200 d. The dominant radial mode also shows variations on the same time-scale, but with much smaller amplitude. In three Kepler RRc stars we detect additional periodicities, with amplitudes below 1 mmag, that must correspond to non-radial g-modes. Such modes never before have been observed in RR Lyrae variables.

  2. Obituary: David Stanley Evans, 1916-2004

    Science.gov (United States)

    Bash, Frank N.

    2005-12-01

    headquartered in Cape Town, South Africa. David had designed and built a Newtonian spectrograph for the 74-inch Radcliffe Telescope with which he measured the first southern galaxy redshifts. David and his family spent 1965-66 in Austin, Texas, where he was a National Science Foundation Senior Visiting Scientist at the University of Texas and McDonald Observatory. They moved permanently to Austin in 1968 and David became a Professor of Astronomy and Associate Director of McDonald Observatory at the University of Texas at Austin. At McDonald Observatory, R. E. Nather had devised a high-speed photometer capable of measuring millisecond time-scale changes in brightness and with Brian Warner, he invented "high-speed astronomy". This instrument caused Evans to revive his occultation program and, over the next twenty years, he produced the major part of the angular diameters of late-type stars with his students and collaborators. In addition, David and collaborators used the extensive collections of the University of Texas to write "Herschel at the Cape". David was also involved in observing the occultation of ? Sco by Jupiter in 1972 and in observing, during a solar eclipse in 1973, the gravitational deflections in the positions of stars whose light passes near to the Sun. The eclipse was observed from Mauritania, and the observations confirmed Einstein's prediction again. David Evans and his students studied late-type stars that have large star-spots and others that flare. In addition, they studied stars whose lunar occultation observations had revealed them to be double or even more than two stars. David Evans's major scientific contribution was an application of his stellar angular diameters to deduce the surface brightness of stars with the result that with suitable color indices one could use photometry to deduce the angular diameter of stars. This is applicable to stars which can never be occulted by the Moon, and its application to Cepheid variable stars has yielded their

  3. Detection of toxigenic Clostridium difficile: comparison of the cell culture neutralization, Xpert C. difficile, Xpert C. difficile/Epi, and Illumigene C. difficile assays.

    Science.gov (United States)

    Pancholi, P; Kelly, C; Raczkowski, M; Balada-Llasat, J M

    2012-04-01

    Clostridium difficile is the most important cause of nosocomial diarrhea. Several laboratory techniques are available to detect C. difficile toxins or the genes that encode them in fecal samples. We evaluated the Xpert C. difficile and Xpert C. difficile/Epi (Cepheid, CA) that detect the toxin B gene (tcdB) and tcdB, cdt, and a deletion in tcdC associated with the 027/NAP1/BI strain, respectively, by real-time PCR, and the Illumigene C. difficile (Meridian Bioscience, Inc.) that detects the toxin A gene (tcdA) by loop-mediated isothermal amplification in stool specimens. Toxigenic culture was used as the reference method for discrepant stool specimens. Two hundred prospective and fifty retrospective diarrheal stool specimens were tested simultaneously by the cell cytotoxin neutralization assay (CCNA) and the Xpert C. difficile, Xpert C. difficile/Epi, and Illumigene C. difficile assays. Of the 200 prospective stools tested, 10.5% (n = 23) were determined to be positive by CCNA, 17.5% (n = 35) were determined to be positive by Illumigene C. difficile, and 21.5% (n = 43) were determined to be positive by Xpert C. difficile and Xpert C. difficile/Epi. Of the 50 retrospective stools, previously determined to be positive by CCNA, 94% (n = 47) were determined to be positive by Illumigene C. difficile and 100% (n = 50) were determined to be positive by Xpert C. difficile and Xpert C. difficile/Epi. Of the 11 discrepant results (i.e., negative by Illumigene C. difficile but positive by Xpert C. difficile and Xpert C. difficile/Epi), all were determined to be positive by the toxigenic culture. A total of 21% of the isolates were presumptively identified by the Xpert C. difficile/Epi as the 027/NAP1/BI strain. The Xpert C. difficile and Xpert C. difficile/Epi assays were the most sensitive, rapid, and easy-to use assays for the detection of toxigenic C. difficile in stool specimens. PMID:22278839

  4. Comparison of Xpert MTB/RIF with other nucleic acid technologies for diagnosing pulmonary tuberculosis in a high HIV prevalence setting: a prospective study.

    Directory of Open Access Journals (Sweden)

    Lesley E Scott

    2011-07-01

    Full Text Available BACKGROUND: The Xpert MTB/RIF (Cepheid non-laboratory-based molecular assay has potential to improve the diagnosis of tuberculosis (TB, especially in HIV-infected populations, through increased sensitivity, reduced turnaround time (2 h, and immediate identification of rifampicin (RIF resistance. In a prospective clinical validation study we compared the performance of Xpert MTB/RIF, MTBDRplus (Hain Lifescience, LightCycler Mycobacterium Detection (LCTB (Roche, with acid fast bacilli (AFB smear microscopy and liquid culture on a single sputum specimen. METHODS AND FINDINGS: Consecutive adults with suspected TB attending a primary health care clinic in Johannesburg, South Africa, were prospectively enrolled and evaluated for TB according to the guidelines of the National TB Control Programme, including assessment for smear-negative TB by chest X-ray, clinical evaluation, and HIV testing. A single sputum sample underwent routine decontamination, AFB smear microscopy, liquid culture, and phenotypic drug susceptibility testing. Residual sample was batched for molecular testing. For the 311 participants, the HIV prevalence was 70% (n = 215, with 120 (38.5% culture-positive TB cases. Compared to liquid culture, the sensitivities of all the test methodologies, determined with a limited and potentially underpowered sample size (n = 177, were 59% (47%-71% for smear microscopy, 76% (64%-85% for MTBDRplus, 76% (64%-85% for LCTB, and 86% (76%-93% for Xpert MTB/RIF, with specificities all >97%. Among HIV+ individuals, the sensitivity of the Xpert MTB/RIF test was 84% (69%-93%, while the other molecular tests had sensitivities reduced by 6%. TB detection among smear-negative, culture-positive samples was 28% (5/18 for MTBDRplus, 22% (4/18 for LCTB, and 61% (11/18 for Xpert MTB/RIF. A few (n = 5 RIF-resistant cases were detected using the phenotypic drug susceptibility testing methodology. Xpert MTB/RIF detected four of these five cases (fifth case

  5. [Rifampicin-resistant Mycobacterium bovis BCG strain isolated from an infant with NEMO mutation].

    Science.gov (United States)

    Çavuşoğlu, Cengiz; Edeer Karaca, Neslihan; Azarsız, Elif; Ulusoy, Ezgi; Kütükçüler, Necil

    2015-04-01

    It is well known that disseminated Mycobacterium bovis BCG infection is developed after BCG vaccination in infants with congenital cellular immune deficiencies such as mutations in genes along the interleukin (IL)-12/interferon (IFN)-γ pathway and mutations in nuclear factor-kB essential modulator (NEMO). In this report, a rifampicin-resistant M.bovis BCG strain isolated from an infant with NEMO defect was presented. An 8-month-old male infant with NEMO defect admitted to the pediatric outpatient clinic of our hospital with fever, generalized lymphadenopathy and hepatosplenomegaly. Microscopic examination of the smears prepared from lymph node and liver biopsy specimens revealed abundant amount (3+) of acid-fast bacilli (AFB). Rifampicin-susceptible Mycobacterium tuberculosis complex (MTC) was detected by real-time PCR (GeneXpert MTB/RIF; Cepheid, USA) in the samples. The growth of mycobacteria was determined on the 20th day of culture performed in MGIT960 system (Becton Dickinson, USA). The isolate was identified as M.bovis BCG by GenoType MTBC kit (Hain Lifescience, Germany) and defined as M.bovis BCG [SIT 482 (BOV_1)] by spoligotyping. In the primary anti-tuberculosis drug susceptibility test performed by MGIT960 system, the isolate was found susceptible to rifampicin (RIF), isoniazid (INH), streptomycin (STM) and ethambutol (EMB). Then anti-tuberculosis treatment was started to the patient. However, the patient at the age of 2 years, re-admitted to the hospital with the complaint of hepatosplenomegaly. Smear of spontaneously draining abscess material obtained from subcutaneous nodules revealed intensive AFB positivity (3+) once again. In the present instance RIF-resistant MTC was detected with GeneXpert system in the specimen. The growth of mycobacteria was determined on the 13th day of culture and isolate was identified as M.bovis BCG. The present isolate was found susceptible to INH, STM and EMB but resistant to RIF. A mutation in the rpoB gene (codon 531, S

  6. A Diagnostic Algorithm for the Detection of Clostridium difficile-Associated Diarrhea

    Science.gov (United States)

    Yoldaş, Özlem; Altındiş, Mustafa; Cufalı, Davut; Aşık, Gülşah; Keşli, Recep

    2016-01-01

    Background: Clostridium difficile is a common cause of hospital-acquired diarrhea, which is usually associated with previous antibiotic use. The clinical manifestations of C. difficile infection (CDI) may range from mild diarrhea to fulminant colitis. Clostridium difficile should be considered in diarrhea cases with a history of antibiotic use within the last 8 weeks (community-associated CDI) or with a hospital stay of at least 3 days, regardless of the duration of antibiotic use (hospital-acquired CDI). Aims: This study investigated the frequency of CDI in diarrheic patients and evaluated the efficacy of the triple diagnostic algorithm that is proposed here for C. difficile detection. Study Design: Cross-sectional study. Methods: In this study, we compared three methods currently employed for C. difficile detection using 95 patient stool samples: an enzyme immunoassay (EIA) for toxin A/B (C. diff Toxin A+B; Diagnostic Automation Inc.; Calabasas, CA, USA), an EIA for glutamate dehydrogenase (GDH) (C. DIFF CHEK-60TM, TechLab Inc.; Blacksburg, VA, USA), and a polymerase chain reaction (PCR)-based assay (GeneXpert® C. difficile; Cepheid, Sunnyvale, CA, USA) that detects C. difficile toxin genes and conventional methods as well. In this study, 50.5% of the patients were male, 50 patients were outpatients, 32 were from inpatient clinics and 13 patients were from the intensive care unit. Results: Of the 95 stool samples tested for GDH, 28 were positive. Six samples were positive by PCR, while nine samples were positive for toxin A/B. The hypervirulent strain NAP-1 and binary toxin was not detected. The rate of occurrence of toxigenic C. difficile was 5.1% in the samples. Cefaclor, ampicillin-sulbactam, ertapenem, and piperacillin-tazobactam were the most commonly used antibiotics by patients preceding the onset of diarrhea. Among the patients who were hospitalized in an intensive care unit for more than 7 days, 83.3% were positive for CDI by PCR screening. If the PCR

  7. A low complexity rapid molecular method for detection of Clostridium difficile in stool.

    Science.gov (United States)

    McElgunn, Cathal J; Pereira, Clint R; Parham, Nicholas J; Smythe, James E; Wigglesworth, Michael J; Smielewska, Anna; Parmar, Surendra A; Gandelman, Olga A; Brown, Nicholas M; Tisi, Laurence C; Curran, Martin D

    2014-01-01

    Here we describe a method for the detection of Clostridium difficile from stool using a novel low-complexity and rapid extraction process called Heat Elution (HE). The HE method is two-step and takes just 10 minutes, no specialist instruments are required and there is minimal hands-on time. A test method using HE was developed in conjunction with Loop-mediated Isothermal Amplification (LAMP) combined with the real-time bioluminescent reporter system known as BART targeting the toxin B gene (tcdB). The HE-LAMP-BART method was evaluated in a pilot study on clinical fecal samples (tcdB(+), n = 111; tcdB(-), n= 107). The HE-LAMP-BART method showed 95.5% sensitivity and 100% specificity against a gold standard reference method using cytotoxigenic culture and also a silica-based robotic extraction followed by tcdB PCR to control for storage. From sample to result, the HE-LAMP-BART method typically took 50 minutes, whereas the PCR method took >2.5 hours. In a further study (tcdB(+), n = 47; tcdB(-), n= 28) HE-LAMP-BART was compared to an alternative commercially available LAMP-based method, Illumigene (Meridian Bioscience, OH), and yielded 87.2% sensitivity and 100% specificity for the HE-LAMP-BART method compared to 76.6% and 100%, respectively, for Illumigene against the reference method. A subset of 27 samples (tcdB(+), n = 25; tcdB(-), n= 2) were further compared between HE-LAMP-BART, Illumigene, GeneXpert (Cepheid, Sunnyvale, CA) and RIDA®QUICK C. difficile Toxin A/B lateral flow rapid test (R-Biopharm, Darmstadt, Germany) resulting in sensitivities of HE-LAMP-BART 92%, Illumigene 72% GeneXpert 96% and RIDAQuick 76% against the reference method. The HE-LAMP-BART method offers the advantages of molecular based approaches without the cost and complexity usually associated with molecular tests. Further, the rapid time-to-result and simple protocol means the method can be applied away from the centralized laboratory settings. PMID:24416173

  8. A low complexity rapid molecular method for detection of Clostridium difficile in stool.

    Directory of Open Access Journals (Sweden)

    Cathal J McElgunn

    Full Text Available Here we describe a method for the detection of Clostridium difficile from stool using a novel low-complexity and rapid extraction process called Heat Elution (HE. The HE method is two-step and takes just 10 minutes, no specialist instruments are required and there is minimal hands-on time. A test method using HE was developed in conjunction with Loop-mediated Isothermal Amplification (LAMP combined with the real-time bioluminescent reporter system known as BART targeting the toxin B gene (tcdB. The HE-LAMP-BART method was evaluated in a pilot study on clinical fecal samples (tcdB(+, n = 111; tcdB(-, n= 107. The HE-LAMP-BART method showed 95.5% sensitivity and 100% specificity against a gold standard reference method using cytotoxigenic culture and also a silica-based robotic extraction followed by tcdB PCR to control for storage. From sample to result, the HE-LAMP-BART method typically took 50 minutes, whereas the PCR method took >2.5 hours. In a further study (tcdB(+, n = 47; tcdB(-, n= 28 HE-LAMP-BART was compared to an alternative commercially available LAMP-based method, Illumigene (Meridian Bioscience, OH, and yielded 87.2% sensitivity and 100% specificity for the HE-LAMP-BART method compared to 76.6% and 100%, respectively, for Illumigene against the reference method. A subset of 27 samples (tcdB(+, n = 25; tcdB(-, n= 2 were further compared between HE-LAMP-BART, Illumigene, GeneXpert (Cepheid, Sunnyvale, CA and RIDA®QUICK C. difficile Toxin A/B lateral flow rapid test (R-Biopharm, Darmstadt, Germany resulting in sensitivities of HE-LAMP-BART 92%, Illumigene 72% GeneXpert 96% and RIDAQuick 76% against the reference method. The HE-LAMP-BART method offers the advantages of molecular based approaches without the cost and complexity usually associated with molecular tests. Further, the rapid time-to-result and simple protocol means the method can be applied away from the centralized laboratory settings.

  9. La mujer en la astronomía: pasado y presente

    Science.gov (United States)

    Dubner, G.

    There exists a long and honorable tradition of participation of women in astronomy, affording many significant contributions to the field. Historically, however, many of these contributions have remained ignored, or recorded under the names of husbands, brothers or bosses. The present report includes an historical perspective, summarizing some of the most signicant contributions done along the last three centuries by female astronomers. Briefly: Catherina Hevelius (1646-1693), author of the largest and last stars catalog made without the aid of a telescope; Nicole-Reine Lepaute (1723-1788) extraordinary mathematician who predicted the path of Halley's Comet in 1757; Caroline Herschel (1750-1848) assistant of her brother William, discovered 8 comets, reduced the positions to a common epoch and published the catalog of 2500 nebulae observed by her brother, was elected honorary member of the Royal Astronomical Society (RAS); Maria Mitchell (1818-1889), professor of astronomy and director of the Vassar College Observatory, dedicated her life to women's education; Williamina Fleming (1857-1911)discovered 94 of the 107 Wolf-Rayet stars known at her time, the bulk of the first HD catalog was based on her spectral types classification; Annie Cannon (1863-1941) examined and classified nearly 500.000 stars, rearranged Fleming's spectral system, defining the OBAFGKM series; Henrietta Swan Leavitt (1868-1921) worked cataloging variable stars, discovered the period-luminosity relations in Cepheids; Cecilia Payne-Gaposhkin combined observations with theory to obtain a temperature scale for Cannon's spectral types; Ruby Payne-Scott (1912-1981), the first female radioastronomer in the world, developed the theory of aperture synthesis, in which most of the larger radio interferometers are based. The present trends are analized based on statistics of the International Astronomical Union (IAU): women represent 11.8% of the total of IAU members; in Argentina the percentage is 33

  10. Supervised detection of anomalous light curves in massive astronomical catalogs

    International Nuclear Information System (INIS)

    but rare objects such as eclipsing Cepheids, blue variables, cataclysmic variables, and X-ray sources. For some outliers there was no additional information. Among them we identified three unknown variability types and a few individual outliers that will be followed up in order to perform a deeper analysis.

  11. Variable stars in the Magellanic Clouds: results from OGLE and SIRIUS

    Science.gov (United States)

    Ita, Yoshifusa; Tanabé, Toshihiko; Matsunaga, Noriyuki; Nakajima, Yasushi; Nagashima, Chie; Nagayama, Takahiro; Kato, Daisuke; Kurita, Mikio; Nagata, Tetsuya; Sato, Shuji; Tamura, Motohide; Nakaya, Hidehiko; Nakada, Yoshikazu

    2004-01-01

    We have performed a cross-identification between Optical Gravitational Lensing Experiment II (OGLE-II) data and single-epoch Simultaneous three-colour Infrared Imager for Unbiased Surveys (SIRIUS) near-infrared (NIR) JHK survey data in the Large and Small Magellanic Clouds (LMC and SMC, respectively). After eliminating obvious spurious variables, variables with too few good data and variables that seem to have periods longer than the available baseline of the OGLE-II data, we determined the pulsation periods for 8852 and 2927 variables in the LMC and SMC, respectively. Based on these homogeneous data, we studied the pulsation properties and metallicity effects on period-K magnitude (PK) relations by comparing the variable stars in the LMC and SMC. The sample analysed here is much larger than the previous studies, and we found the following new features in the PK diagram. (1) Variable red giants in the SMC form parallel sequences on the PK plane, just like those found by Wood in the LMC. (2) Both sequences A and B of Wood have discontinuities, and they occur at the K-band luminosity of the tip of the red giant branch. (3) The sequence B of Wood separates into three independent sequences B+/- and C'. (4) A comparison between the theoretical pulsation models and observational data suggests that the variable red giants on sequences C and newly discovered C' are pulsating in the fundamental and first overtone modes, respectively. (5) The theory cannot explain the pulsation mode of sequences A+/- and B+/-, and they are unlikely to be the sequences for the first and second overtone pulsators, as was previously suggested. (6) The zero-points of PK relations of Cepheids in the metal deficient SMC are fainter than those of the LMC by ~0.1 mag but those of SMC Miras are brighter than those of the LMC by ~0.13 mag (adopting the distance modulus offset between the LMC and SMC to be 0.49 mag and assuming the slopes of the PK relations are the same in the two galaxies), which are

  12. A Photometric and Spectroscopic Survey of AGB Stars in M31

    Science.gov (United States)

    Brewer, James P.

    1996-04-01

    Asymptotic giant-branch (AGB) stars are identified and classified in five 7' X 7' fields spaced along M31's SW semi-major axis using a four band photometric system. An investigation of the AGB luminosity functions and red giant-branch widths reveals significant differences between the star forming histories of the five fields. The distance modulus of M31 is derived using carbon stars (C-stars) and found to be consistent with both a value obtained from Cepheids and with values in the literature. The ratio of AGB C- to M-stars (C/M ratio) in the five fields is found to increase with galactocentric distance and it is shown that photometric incompleteness is not responsible for this effect. This is the first clear demonstration of a varying C/M ratio in an external galaxy. The C/M ratios appear to be insensitive to star-forming history differences but sensitive to metallicity differences between the fields. Previous observations are used to define a relationship between the C/M ratio and metallicity, and this is used to obtain estimates of the field metallicities. These estimates are found to be consistent with a previous measurement of M31's metallicity gradient. The C/M ratios measured in M31 indicate that the composition of M31's interstellar medium may be position dependent, and evidence is cited in favour of this. Follow up spectroscopy was obtained in two of the five fields, and is used to show that the photometric system did an excellent job of discriminating between M-, S- and C-stars. Of the 48 C-stars for which spectra were obtained, 7 have strongly enhanced 13C bands (J-stars), 2 have strong H-alpha emission, while 3 are found to exhibit enhanced Li absorption (Li-stars). Both the J- and Li-stars are fainter than predicted by current theoretical models, while the colours of the H-alpha stars suggest they may be in the terminal phases of their evolution. The C_2 and CN bandstrengths of the C-stars are measured, and no correlation between these bandstrengths

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

    International Nuclear Information System (INIS)

    We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud” (SAGE-SMC) and the “Spitzer Survey of the Small Magellanic Cloud” (S3MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer’s InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 μm bands, and the Multiband Imaging Photometer for Spitzer 24 μm band. An error-weighted flux difference between each pair of three epochs (“variability index”) is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ∼2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-02-01

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

  15. Searching gravitational microlensing events in the galaxy spiral arms by EROS II; Recherche d'evenements de microlentille gravitationnelle dans les bras spiraux de la galaxie avec EROS II

    Energy Technology Data Exchange (ETDEWEB)

    Derue, Frederic [Paris-11 Univ., 91 Orsay (France)

    1999-04-15

    The EROS II experiment is searching for microlensing events due to compact massive objects passing through the line-of-sight of luminous stars. These objects are candidates to explain the baryonic component of Dark Matter in our Galaxy. EROS II was dedicated to different lines-of-sight: Small and Large Magellanic Clouds, Galactic Centre and 4 directions towards the Spiral Arms of the Galaxy. This thesis presents the first search for microlensing towards these last lines-of-sight (about 9 million stars). Simple criteria based on the search for significant fluctuations allowed one to discover a low noise sample of 7 candidates to the microlensing effect, with an average timescale of 50 days. A detailed analysis of the light curve of one candidate allows us to give a confidence interval on its mass 2.7 x 10{sup -3} < M/M{sub 0} < 0.84 at 95% CL. The amplification curve of another candidate shows a modulation which can be interpreted as a microlensing effect acting on a binary source, with an orbital period of P{sub 0} = 50 {+-} 3 days. To improve the knowledge of the distance of the target stars, we have combined observations of EROS II with bibliographic sources on associations of stars linked with the spiral arm features, and we have developed a program to find variable stars. Ten cepheids have thus been found. Distances obtained with different methods are in rough agreement with each other. The average optical depth measured towards the four directions is {tau}-bar = 0.45{sub 0.11}{sup +0.23} x 10{sup -6}. It is compatible with expectations from simple galactic models. The long duration of most events favours interpretation of lensing by objects belonging to the disk instead of the halo. It also seems that some events due to bulge lenses have influenced measurements towards the line-of-sight which is closest to the Galactic Centre. Observation continue towards spiral arms. More accurate measurements should be obtained with increase of statistics, allowing one to

  16. The Ks-band Tully–Fisher Relation – A Determination of the Hubble Parameter from 218 ScI Galaxies and 16 Galaxy Clusters

    Indian Academy of Sciences (India)

    David G. Russell

    2009-06-01

    The value of Hubble parameter (H0) is determined using the morphologically type dependent Ks-band Tully–Fisher Relation (K-TFR). The slope and zero point are determined using 36 calibrator galaxies with ScI morphology. Calibration distances are adopted from direct Cepheid distances, and group or companion distances derived with the Surface Brightness Fluctuation Method or Type Ia Supernova. It is found that a small morphological type effect is present in the K-TFR such that ScI galaxies are more luminous at a given rotational velocity than Sa/Sb galaxies and Sbc/Sc galaxies of later luminosity classes. Distances are determined to 16 galaxy clusters and 218 ScI galaxies with minimum distances of 40.0 Mpc. From the 16 galaxy clusters a weighted mean Hubble parameter of H0 = 84.2 ± 6 km s-1 Mpc-1 is found. From the 218 ScI galaxies a Hubble parameter of H0 = 83.4 ± 8 km s-1 Mpc-1 is found. When the zero point of K-TFR is corrected to account for recent results that find a Large Magellanic Cloud distance modulus of 18.39 × 0.05, a Hubble parameter of 88.0 ± 6 km s-1 Mpc-1 is found. Effects from Malmquist bias are shown to be negligible in this sample as galaxies are restricted to a minimum rotational velocity of 150 km s-1. It is also shown that the results of this study are negligibly affected by the adopted slope for the K-TFR, inclination binning, and distance binning. A comparison with the results of the Hubble Key Project (Freedman et al. 2001) is made. Discrepancies between the K-TFR distances and the HKP I-TFR distances are discussed. Implications for -CDM cosmology are considered with H0 = 84 km s-1 Mpc-1. It is concluded that it is very difficult to reconcile the value of H0 found in this study with ages of the oldest globular clusters and matter density of the universe derived from galaxy clusters in the context of -CDM cosmology.

  17. THE TIP OF THE RED GIANT BRANCH DISTANCES TO TYPE Ia SUPERNOVA HOST GALAXIES. II. M66 AND M96 IN THE LEO I GROUP

    International Nuclear Information System (INIS)

    M66 and M96 in the Leo I Group are nearby spiral galaxies hosting Type Ia supernovae (SNe Ia). We estimate the distances to these galaxies from the luminosity of the tip of the red giant branch (TRGB). We obtain VI photometry of resolved stars in these galaxies from F555W and F814W images in the Hubble Space Telescope archive. From the luminosity function of these red giants, we find the TRGB I-band magnitude to be ITRGB = 26.20 ± 0.03 for M66 and 26.21 ± 0.03 for M96. These values yield distance modulus (m – M)0 = 30.12 ± 0.03(random) ± 0.12(systematic) for M66 and (m – M)0 = 30.15 ± 0.03(random) ± 0.12(systematic) for M96. These results show that they are indeed the members of the same group. With these results we derive absolute maximum magnitudes of two SNe (SN 1989B in M66 and SN 1998bu in M96). V-band magnitudes of these SNe Ia are ∼0.2 mag fainter than SN 2011fe in M101, one of the nearest recent SNe Ia. We also derive near-infrared magnitudes for SN 1998bu. Optical magnitudes of three SNe Ia (SN 1989B, SN 1998bu, and SN 2011fe) based on TRGB analysis yield a Hubble constant, H0 = 68.4 ± 2.6(random) ± 3.7(systematic) km s–1 Mpc–1. This value is similar to the values derived from recent WMAP9 results, H0 = 69.32 ± 0.80 km s–1 Mpc–1, and from Planck results, H0 = 67.3 ± 1.2 km s–1 Mpc–1, but smaller than other recent determinations based on Cepheid calibration for SNe Ia luminosity, H0 = 74 ± 3 km s–1 Mpc–1

  18. The Carina Project IX: On Hydrogen and Helium Burning Variables

    Science.gov (United States)

    Coppola, G.; Marconi, M.; Stetson, P. B.; Bono, G.; Braga, V. F.; Ripepi, V.; Dall'Ora, M.; Musella, I.; Buonanno, R.; Fabrizio, M.; Ferraro, I.; Fiorentino, G.; Iannicola, G.; Monelli, M.; Nonino, M.; Thévenin, F.; Walker, A. R.

    2015-11-01

    We present new multiband (UBVI) time-series data of helium burning variables in the Carina dwarf spheroidal galaxy. The current sample includes 92 RR Lyrae—six of them are new identifications—and 20 Anomalous Cepheids, one of which is new identification. The analysis of the Bailey diagram shows that the luminosity amplitude of the first overtone component in double-mode variables is located along the long-period tail of regular first overtone variables, while the fundamental component is located along the short-period tail of regular fundamental variables. This evidence further supports the transitional nature of these objects. Moreover, the distribution of Carina double-mode variables in the Petersen diagram (P1/P0 versus P0) is similar to metal-poor globulars (M15, M68), to the dwarf spheroidal Draco, and to the Galactic Halo. This suggests that the Carina old stellar population is metal-poor and affected by a small spread in metallicity. We use trigonometric parallaxes for five field RR Lyrae stars to provide an independent estimate of the Carina distance using the observed reddening free Period-Wesenheit [PW, (BV)] relation. Theory and observations indicate that this diagnostic is independent of metallicity. We found a true distance modulus of μ = 20.01 ± 0.02 (standard error of the mean) ± 0.05 (standard deviation) mag. We also provided independent estimates of the Carina true distance modulus using four predicted PW relations (BV, BI, VI, BVI) and we found: μ = (20.08 ± 0.007 ± 0.07) mag, μ = (20.06 ± 0.006 ± 0.06) mag, μ = (20.07 ± 0.008 ± 0.08) mag, and μ = (20.06 ± 0.006 ± 0.06) mag. Finally, we identified more than 100 new SX Phoenicis stars that together with those already known in the literature (340) make Carina a fundamental laboratory for constraining the evolutionary and pulsation properties of these transitional variables.

  19. Microbial Monitoring of Pathogens by Comparing Multiple Real-Time PCR Platforms for Potential Space Applications

    Science.gov (United States)

    Birmele, Michele

    2012-01-01

    The International Space Station (ISS) is a closed environment wih rotations of crew and equipment each introducing their own microbial flora making it necessary to monitor the air, surfaces, and water for microbial contamination. Current microbial monitoring includes labor and time intensive methods to enumerate total bacterial and fungal cells with limited characterization during in-flight testing. Although this culture-based method has been sufficient for monitoring the ISS, future long duration missions will need to perform more comprehensive characterization in-flight, since sample return and ground characterization may not be available. A workshop was held in 2011 at the Johnson Space Center to discuss alternative methodologies and technologies suitable for microbial monitoring for these longterm exploration missions where molecular-based methodologies, such as polymerase chain reaction (PCR), were recommended. In response, a multi-center (Marshall Space Flight Center, Johnson Space Center, Jet Propulsion Laboratory, and Kennedy Space Center) collaborative research effort was initiated to explore novel commercial-off-the-shelf hardware options for spaceflight environmental monitoring. The goal was to evaluate quantitative/semi-quantitative PCR approaches to space applications for low cost in-flight rapid identification of microorganisms affecting crew safety. The initial phase of this project identified commercially available platforms that could be minimally modified to perform nominally in microgravity followed by proof-of-concept testing on the highest qualifying candidates with a universally available test organism, Salmonella enterica. The platforms evaluated during proof-of-concept testing included the iCubate 2.0(TradeMark) (iCubate, Huntsville, AL), RAZOR EX (BioFire Diagnostics; Salt Lake City, Utah) and SmartCycler(TradeMark) (Cepheid; Sunnyvale, CA). The analysis identified two potential technologies (iCubate 2.0 and RAZOR EX) that were able to

  20. Astronomers celebrate a year of new Hubble results

    Science.gov (United States)

    1995-02-01

    Space Telescope to make accurate measurements of the distance of Ml 00, a far away galaxy located in the Virgo cluster of galaxies. To do this they used a number of Cepheid variable stars, rare objects that change in brightness over a regular period. Because astronomers know that there is a direct link between the period of the Cepheid's pulsation and its actual brightness, they can do a simple calculation to work out the distance to the object by comparing its actual brightness with how bright it appears to Hubble. The astronomers had to study more than 40,000 stars before finding the 20 Cepheids they used for their calculations. The results revealed that M100 lies 56 million light years from Earth. With this, astronomers calculated that the Universe is expanding at a rate of 80 kilometres per second per megaparsec (a megaparsec is 3,261,600 light years). This is much faster than astronomers had expected. On the basis of this value for the Hubble Constant, the Universe must be aged somewhere between eight and twelve billion years old. But, this flies in the face of established facts. We know there are stars in our Universe that are 16 billion years old - how can they be older than the Universe in which they exist? It could be that the theory that explains the evolution of stars or the Big Bang theory are wrong. Or perhaps it is the observations that are incorrect. Hubble astronomers soon hope to solve this riddle by taking further measurements to refine their figures. "This is a programme that we know is going to give us some really firm answers in the next three to five years," said Dr Macchetto, one of the 15 European astronomers at the Space Telescope Science Institute. "It will take that time to collect and analyse enough data." Part of the Universe is missing ! Once astronomers know the expansion rate of the Universe they will be one step away from determining its fate. But it will be a big step - for astronomers will have to work out the mass of the Universe and