Aavso paper Session I sunday Sunday, May 22, 2011, 9: 30 am – 12: 00 pm
Stars, Star Formation and Associated Topics
Download 2.63 Mb.
|
407Stars, Star Formation and Associated TopicsPoster SessionEssex Ballroom407.01
The Effect Of Limited Spatial Resolution Of Stellar Surface Magnetic Field Maps On Mhd Wind And Coronal X-ray Emission Models Cecilia Garraffo1, O. Cohen1, J. J. Drake1, C. Downs2 1Harvard-Smithsonian CfA, 2Institute for Astronomy, University of Hawaii at Manoa. 8:00 AM - 12:00 PM Essex Ballroom We study the influence of the spatial resolution of solar and stellar surface magnetic field maps on global MHD solar and stellar wind models, and on a model of coronal heating and X-ray emission. For the Sun, we compare the solutions driven by a low-resolution WSO map, the same map with spatial resolution artificially increased by a refinement algorithm, and a high-resolution MDI map. We perform a similar test for the planet-bearing K1-2V star HD 189733, comparing MHD wind solutions and X-ray morphology and flux for a Zeeman-Doppler imaging magnetic map, and the same map with artificially enhanced spatial resolution. In both solar and stellar cases, the large-scale wind structure is dominated by the lower-order magnetic components and is little affected by fine-scale surface magnetic structure. Provided the low-order field is properly resolved, MHD wind models applied to solar-like stars should be reliable. Instead, the X-ray morphology is dominated by the closed loop structure between mixed polarities on smaller scales and shows significant changes between high and low resolution maps. We conclude that three-dimensional modelling of coronal X-ray emission has greater surface magnetic field spatial resolution requirements than wind modeling, and can be unreliable unless the dominant mixed polarity magnetic flux is properly resolved. 407.02
8:00 AM - 12:00 PM Essex Ballroom We use axisymmetric magnetohydrodynamics (MHD) to investigate the launching and collimation of jets emerging from the disk-magnetosphere boundary of accreting magnetized stars. Our analysis shows that the emergence of a collimated jet is a two-step process: first, the matter is accelerated along field lines extending up from the disk by the magnetic pressure force. Then, the matter is collimated by the toroidal magnetic field in the stellar corona. The jet emerges from the disk-magnetosphere boundary and is weakly matter dominated. The matter in the jet crosses the Alfven and fast magnetosonic surfaces a few stellar radii above the disk. Even far from the disk, the magnetic force continues to accelerate and collimate the jet. We observe a matter ejection-to-accretion ratio of ~0.25 in steady state. A high accretion rate can generate the strong magnetic pressure which drives the matter from the disk and as such, these simulations may apply to EXor and FUOR class stars which undergo episodes of enhanced accretion. In general, the models can be applied to many types of magnetized stars--white dwarfs, neutron stars, and brown dwarfs--which exhibit periods of enhanced accretion. 407.03
8:00 AM - 12:00 PM Essex Ballroom The short dispersal timescales of the planet-forming gas in disks hampers its detection. Although ro-vibrational CO is observed in HAeBe disks, CO(3-2) is less frequent, and is often contaminated by diffuse emission in single-dish data. CO(6-5) traces gas at intermediate temperatures between the cold molecular gas that originates CO(3-2), and the hotter inner-rim gas seen in the IR ro-vibrational lines. Neutral carbon, C I (2-1), is a tracer of the atomic phase in disks. No C I (2-1) detections in disks exist in the literature. Our objectives are to identify new gas-rich systems for ALMA observations of sub-mm high-J CO, and search for C I. As a followup to a CO(3-2) survey in protoplanetary disks, we acquired CHAMP+ maps in CO(6-5) 691.4 GHz and C I(2-1)809 GHz. We obtained interesting upper limits in four targets and one CO(6-5) detection in HD142527. No neutral carbon was detected. In this poster we present our main results, and discuss their implications. 407.04
8:00 AM - 12:00 PM Essex Ballroom Intermediate-mass stars form dense and dynamic circumstellar envelopes at the end of their stellar lives. These envelopes can be dramatically asymmetric, with dusty waist formations and wind-blown polar cavities. Several IR spectral features are predicted to evolve as the post-AGB phase unfolds, many of which can be used as tracers of circumstellar structure. I will present recent investigations of this phenomenon using 5-40 micron spectra from Spitzer’s Infrared Spectrograph (IRS). 407.05
Spectropolarimetric Study of SN2004dt Alejandro Clocchiatti1, P. A. Zelaya1, J. L. Quinn1, D. Baade2, P. Hoeflich3, J. Maund4, F. Patat2, L. Wang5, J. C. Wheeler6 1Univ. Catolica De Chile, Chile, 2European Southern Observatory, Germany, 3Florida State University, 4Dark Cosmology Centre Niels Bohr Institute, Denmark, 5Texas A&M University, 6University of Texas at Austin. 8:00 AM - 12:00 PM Essex Ballroom We present spectropolarimetric observations of SN 2004dt obtained with the Very Large Telescope of the European Southern Observatory when the supernova was approximately at -7, 7, 13, and 36 days after maximum light. We confirm and extend the results of Wang et al. (2006, Ap.J, 653, 490) who analyzed the pre-maximum spectrum. The strong Si II 6355 line polarization that SN2004dt displayed before maximum followed the usual behavior in Type Ia SNe, first increasing and then decreasing with time, eventually disappearing together with the Si II lines in the last spectrum. Phase by phase, however, it is the strongest we have seen in any SN Ia, departing significantly from the typical trend of other SNe. The evolution in time of the feature confirms the picture based on the first spectrum, that the asymmetric silicon structure extends from very high to normal velocities (~22,000 to ~8,000 km/s, although the maximum polarization stays at moderately high velocity (~13,500 km/s). The line polarization of the low velocity Ca II triplet (at ~16,000 km/s), on the other hand, stays at ~1.0% during the photospheric phase and then increases by a factor of more than two, being strongest in our latest observation. The mean velocity of the polarized feature does not show major variations. All the major polarized features share an orientation angle of, approximately, 135 degrees. In addition, the Q-U diagrams at the different phases also confirm the picture that the major radially extended structure that causes the line polarization is clumpy, or broken in smaller pieces. The findings sustain the picture that the explosion of this SN produced ejecta with some major asymmetry, as well as a clumpy distribution, in some of the chemical species. We discuss our results in the context of the currently favored models of Type Ia SN explosions. 407.07
Kepler observations of NGC 6826 Peter Stine1, N. Jevtic1, W. Nilsen1 1Bloomsburg Univ.. 8:00 AM - 12:00 PM Essex Ballroom Long cadence data from the Kepler Space telescope are presented for KIC 12071221. The object consists of a ZZ Leporis star surrounded by the planetary nebula, NGC 6826. Power spectra reveal several prominent lines, many of which do not persist over different quarters. Second quarter observations revealed lines at 9.375 mHz and 18.75 mHz, possibly a fundamental and first harmonic, which correspond to timescales of 15 and 30 hours. These lines are not apparent in the third quarter, but the 18.75 mHz line re-appeared in later quarters. The results indicate that turbulence on sampling timescales is present. This will be tested on short cadence data that are expected shortly. 407.08
Daniel Castro1 1Harvard Smithsonian Center for Astrophysics. 8:00 AM - 12:00 PM Essex Ballroom We investigate the effects of the efficient production of cosmic rays on the evolution of supernova remnants (SNRs) in the adiabatic Sedov-Taylor phase. We model the SNR by coupling the hydrodynamic evolution with nonlinear diffusive shock acceleration (DSA), and track self-consistently the ionization state of the shock-heated plasma. Using a plasma emissivity code and the results of the model, we predict the thermal X-ray emission and combine it with the non-thermal component in order to obtain the complete spectrum in this energy range. Hence, we study how the interpretation of thermal X-ray observations is affected by the efficiency of the DSA process, and find that, compared to test particle cases, the efficient DSA example yields a smaller shock radius and speed, a larger compression ratio, and lower intensity X-ray thermal emission. We also find that a model where the shock is not assumed to produce cosmic rays can fit the X-ray observational properties of an example with efficient particle acceleration, with a different set of input parameters, and in particular a much lower explosion energy. Additionally, we model the broadband non-thermal emission, and investigate what signatures result from the acceleration of particles. 407.09
8:00 AM - 12:00 PM Essex Ballroom Knowing the properties of turbulence and their physical origins is necessary for our complete understanding of star formation within molecular clouds. However, until recently, there were no analytic models specific to compressible turbulence, and most work focused on adapting what is known from incompressible fluids, such as the Kolmogorov four-fifths law. Using data from a large-scale three-dimensional simulation of supersonic (M=6) isothermal turbulence, we verify an exact flux relation derived analytically from the Navier-Stokes equations by Falkovich, Fouxon, and Oz [Journal of Fluid Mechanics 644, 465 (2010)], which serves as the compressible case analogue of the Kolmogorov four-fifths law. We find strong support for the new relation; recovering both the predicted linear scaling and an excellent agreement with the predicted slope value. 407.10
8:00 AM - 12:00 PM Essex Ballroom We report the first sub-arc second (0.65" x 0.51") image of the dimethyl ether (CH3)2O molecule toward the Orion Kleinmann-Low nebula (Orion--KL). The observations have been carried at 43.4 GHz with the Expanded Very Large Array (EVLA). The distribution of the lower energy transition 6(1,5) - 6(0,6), EE; Eu = 21K mapped in this study is in excellent agreement with the published dimethyl ether and methyl formate emission images obtained with a lower resolution. The main emission peaks are observed toward the Compact Ridge and Hot Core southwest components, as the northern parts of the Compact Ridge and in an intermediate position between the Compact Ridge and the Hot Core. Our study shows that higher spectral resolution (WIDAR correlator) and increased spectral coverage provided by the EVLA offer new possibilities for imaging complex molecular species. The sensitivity improvement and the other EVLA improvements make this instrument well suited for high sensitivity, high angular resolution, molecular line imaging. 407.11
8:00 AM - 12:00 PM Essex Ballroom Young low-mass stars host intense magnetic fields that play an important role in regulating the mass and angular momentum transfer between the star and its circumstellar disk, and at the same time heat and confine hot stellar coronae. The X-ray emission from the coronal plasma in turn heats and ionizes the circumstellar disk, affecting its properties and evolution. In June 2009 we have conducted a coordinated multiwavelength observing campaign targeting V2129 Oph, a K5 classical T Tauri star (CTTS), with the goal of simultaneously determining the properties of its X-ray emitting plasma, the structure of its large-scale magnetic field, and the characteristics of its accretion flow. We present here a study of the X-ray emitting plasma of V2129 Oph based on a 200 ks Chandra/HETG observation. We find that V2129 Oph hosts high-density plasma at temperature of 3-4 MK, likely heated in an accretion shock, and an hotter "coronal" plasma component (T > 10 MK). A bright X-ray flare detected during the observation can be attributed to this latter component and was likely produced by a large coronal loop with half length > 3 R_star. The detection of high-density plasma on V2129 Oph confirms that such plasma component is commonly found on CTTSs, when observed with high resolution X-ray spectroscopy. The X-ray emission from the cool high-density plasma is seen to vary during the 200 ks Chandra observation: high density and high emission measure are observed during the first 100 ks, low density and lower emission measure during the last 100 ks. We can naturally interpret these observations attributing the high density plasma to the accretion shock and the observed variability to the changing viewing geometry of the accretion shock during the stellar rotation, as constrained from simultaneous optical observations. 407.12
Search For And Characterization Of Galactic Star Clusters With 2MASS And Pan-STARRS 1 Chien-Cheng Lin1, E. Magnier1, W. Chen2 1Institute for Astronomy, HI, 2Graduate Institute of Astronomy, NCU, Taiwan. 8:00 AM - 12:00 PM Essex Ballroom We plan to conduct a comprehensive search for uncatalogued galactic open clusters using Pan-STARRS (Panoramic Survey Telescope And Rapid Response System) data in five optical bands (g, r, i, z, y) to a depth of ~24 magnitude, about 100 times more sensitive than currently available surveys. A ``star-count'' pipeline has been tested on the 2MASS point-source catalog. In a demonstration region with a sky coverage between galactic longitude 2 < l < 358 degrees and galactic latitude |b| < 50 degrees, we identified 502 cluster candidates. Of these, two are galaxies, 32 (6.3%) are cluster of galaxies, 91 (18.1%) are globular clusters, and 360 (71.7%) are open clusters. Seventeen (3.3%) of our candidates are newly identified. Overall, the detection rate of stellar clusters using our algorithm is about 90%. In addition, we have characterized some of the fundamental parameters of clusters, such as age and distance, using the Pan-STARRS 1 photometry, and the results are in good agreement with previous results. 407.13
8:00 AM - 12:00 PM Essex Ballroom Open clusters are key tracers of the Milky Way. We examine how current and upcoming surveys will expand the use of open clusters as tools to study the Galaxy. These surveys will provide new data (e.g., deep photometry, proper motions, chemical abundances) for not just one or two clusters, but hundreds or even over a thousand open clusters, all with high quality uniform data. 407.14
8:00 AM - 12:00 PM Essex Ballroom We present our latest generation of evolutionary models for very low-luminosity stars (near the ends of their respective Main Sequences) and for Brown Dwarfs. These results have been computed for a wide range of metallicities which includes extremely old subdwarfs (0.0001 < Z < 0.02). Using sophisticated atmospheric models from the Allard-Hauschildt library, we precompute an extensive grid of outer boundary conditions and then interpolate this grid as the models are being calculated. Using very sophisticated input physics such as the OPAL opacities, the Alexander and Ferguson low-temperature opacities, and our own equation of state which is largely derived from that of the SCVH low-temperature EOS, we have calculated the evolution of low-mass stars and Brown Dwarfs ranging from 0.001 to 0.5 solar masses. The physical properties of these models will be presented and the observational implications will be discussed briefly. 407.15
The Chromospheric Activity and Age Relation among Main Sequence Stars in Wide Binaries Terry D. Oswalt1, J. Zhao1 1Florida Institute of Technology. 8:00 AM - 12:00 PM Essex Ballroom We present a study of the chromospheric activity levels in 36 wide binary systems. Thirty one of the binaries contain a white dwarf component. In such binaries the total age can be estimated by adding the cooling age of the white dwarf to an estimate of the progenitor’s main sequence lifetime. To better understand how activity correlates to stellar age, 14 cluster member stars were also observed. Our observations confirm the expectation derived from studies of single main sequence stars that activity decays with age. However, for the first time we demonstrate that this relation extends from 50 Myr to at least 8 Gyr for stars with 1.0 < V-I < 2.4 color index. We also find that little change in activity occurs for stars with V-I < 1.0 and ages between 1 Gyr and 5 Gyr. The slope of constant age lines in the activity vs. V-I plane for young stars is relatively steep, while for old stars it appears to be flatter. In addition, our sample includes five wide binaries consisting of two main sequence stars. These pairs provide a useful reality check on our activity vs. age relation. Support for this project from NSF grant AST-0807919 to Florida Institute of Technology is gratefully acknowledged. 407.16
MOST Ultra-high Precision Photometry of delta Capricorni - the Nearest & Brightest Eclipsing Binary with a Pulsating Component: An Important Asteroseismic Laboratory for A-type Stars Edward F. Guinan1, S. G. Engle1, A. Prsa1, R. P. Wasatonic1, F. C. Fekel2, M. Williamson2, J. Matthews3, K. Kolenberg4, M. Breger5 1Villanova Univ., 2Tennessee State Univ., 3MOST / Univ. of British Columbia, Canada, 4CfA, 5Univ. of Vienna, Austria. 8:00 AM - 12:00 PM Essex Ballroom We report on over 3 weeks of continuous ultra-high precision photometry of the bright, nearby, detached (P= 1.02 day; A8m + dK7) eclipsing binary delta Cap. The observations were carried out with the Canadian Micro-satellite MOST during Aug/Sept. 2010. Extensive contemporaneous spectroscopy was secured with the 2-m TSU Automatic Spectroscopic Telescope (AST) and complementary BVR photometry was obtained with ground based telescopes. Delta Cap is an astrophysically important star because it is the nearest and brightest eclipsing binary with a bright pulsating component that can be used (with astereoseismic analyses) to test and calibrate stellar interior and pulsation models. When a pulsating star is a member of an eclipsing binary, the analyses of the it’s light and radial velocity observations yield the precise determination of all fundamental orbital and physical properties for the component stars. Moreover the MOST observations during the primary eclipses are a powerful tool for mode identification as portions of the pulsating A-star are blocked from view. Also because delta Cap is nearby and has a reliable parallax (pi (Hipp) = 84.27+/- 0.19 mas), the component stars’ luminosities and temperatures are also directly determinable. In addition to its well behaved 1.02-d periodic light variations arising from the eclipses and tidal effects, the MOST light curves clearly show small (~0.01-0.02 mag) complex light variations. We present the results of the analysis the eclipsing binary light and radial velocity curves using PHOEBE. Also presented are the initial asteroseismic analyses of the A8m component based on the MOST photometry and contemporaneous radial velocity observations. Preliminary models indicate this star is a hybrid gamma Dor-delta Scuti pulsator. We gratefully acknowledge the support from NASA/MOST Grant NNX10AI85G and NSF/RUI Grant AST-05-07542. We also wholeheartedly thank the MOST team for securing and reducing the photometry. 407.17
The Pulsation Spectra of Kepler B Stars Bernard J. McNamara1, J. Jackiewicz1, J. McAteer1, L. Boucheron1, H. Cao1, D. Voelz1, M. Kirk1, G. Taylor1, K. DeGrave1, A. Al-Ghraibah1, C. Lovekin2, A. Pevtsov1 1New Mexico State Univ., 2Los Alamos National Laboratory. 8:00 AM - 12:00 PM Essex Ballroom The Kepler satellite was designed to obtain single filter light curves of over 100,000 stars during its 3.5 year mission lifetime. The accuracy of each 30 minute measurement is about 20 parts per million for a 12 magnitude star. Although the primary objective of Kepler is to search for the signal of Earth-like planets in these light curves, dozens of pulsating B stars are included among its targets. This poster presents and overview of the techniques used to obtain the frequency spectra of these stars. A data base of stellar pulsation spectra is also presented along with the positions of these stars in the HR diagram. A major limitation of the Kepler data is that it does not allow the spherical harmonic l and m values of the pulsation modes to be determined. To do this multi-color observations or spectra are needed. A list of candidate stars for this type of effort is provided. This work is supported by the NASA Kepler Guest Observer program. 407.18
8:00 AM - 12:00 PM Essex Ballroom RR Lyrae type pulsating variable stars are good distance indicators within the Galaxy and its local neighborhood. Extensive previous work in the optical and more recently in the near-infrared has resulted in predictive period-luminosity (PL) relations with distance modulus uncertainties ~0.15 mag. The PL relations of RR Lyrae are a significant component of the local distance ladder and any improvement in accuracy locally extends out to improved accuracy at cosmological scales. The recently available Wide-field Infrared Survey Explorer (WISE) Preliminary Data Release contains mid-infrared multi-epoch photometry for 77 of the 144 RR Lyrae type variables with Hipparcos-derived distances. Using these stars we derive new mid-infrared period-luminosity relations in the WISE W1 (3.4 µm), W2 (4.6 µm), and W3 (12 µm) bands which combine to yield an average distance modulus uncertainty 0.046 mag, and demonstrate these relations' robustness to metallicity. We anticipate that future similar analysis of RR Lyrae variables in the full WISE dataset could yield PL relations with fractional distance uncertainties <1%. Download 2.63 Mb. Share with your friends:
|